WO2025190816A1

WO2025190816A1 - 3d lorentz type permanent magnet motor

Info

Publication number: WO2025190816A1
Application number: PCT/EP2025/056335
Authority: WO
Inventors: Fidelus Adrianus Boon; Olof Martinus Josephus FISCHER
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2024-03-15
Filing date: 2025-03-07
Publication date: 2025-09-18
Anticipated expiration: 2026-09-15
Also published as: TW202544566A

Abstract

The invention provides a Lorentz type permanent magnet motor comprising a permanent magnet motor, comprising at least one coil assembly and at least one magnet assembly. The at least one magnet assembly comprises a first magnet group comprising two or more primary magnets extending along a first direction and a second magnet group comprising two secondary magnets extending along a second direction which is perpendicular to the first direction. The two or more primary magnets are placed adjacent to each other along the second direction and have alternating polarization directions. A secondary magnet is arranged on each end with respect to the first direction of the first magnet group. The secondary magnets of the second magnet group overlap with at least part of a turning section of the at least one coil assembly seen from a third direction which is perpendicular to the first direction and the second direction.

Description

3D LORENTZ TYPE PERMANENT MAGNET MOTOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP applications 24163768.5 which was filed on 15 March 2024 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a Lorentz type permanent magnet motor capable of providing forces in two or more directions. The present invention further relates to a positioning system for positioning a movable object, a lithographic tool and a method of exerting a force and/or a torque on a movable object.

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] In a lithographic apparatus, motors such as planar motors are used to position the wafer and other movable objects. Such motors can usually provide movement in one or two directions. As movement along three directions (X, Y, Z, wherein X, Y, and Z are orthogonal to each other, X and Y are in the plane of the wafer, and Z is perpendicular to the wafer) is required, multiple motors are applied to expand the number of degrees of freedom to the required number. Such motors/actuators are usually of the Lorentz type. The forces that these motors generate can be divided into an in plane driving force (i.e. a force in the plane of the wafer, the X, Y plane) and an out of plane levitation force (in the Z direction). [0006] These planar motors comprise a coil assembly of multiple coils arranged side by side along a direction in the plane of the coils. The motors also comprise a magnet assembly comprising multiple magnets, also arranged side by side along the same direction as the direction along which the coils are arranged side by side. It is this direction along which the motor can apply the in plane driving force. The magnets have an alternating polarity, for example up-down-up-down or a Halbach array. One of the magnet assembly and the coil assembly is connected to a substantially stationary environment while the other is connected to an object to be moved w.r.t. the substantially stationary environment.

[0007] A disadvantage of these planar motors is that they can only generate force in one in plane direction (i.e. in the X, Y plane) and in the out of plane direction Z. Multiple motors are thus needed to allow force application in both in plane directions. This increases the room required and the mass of the motors.

SUMMARY

[0008] It is an object of the invention to provide a Lorentz type permanent magnet motor capable of providing force in three directions and/or torque around three axes which is more compact than current permanent magnet motors. It is a further object of the invention to provide a positioning system for positioning a movable object in three directions which is more compact than current positioning systems. It is a further object of the invention to provide a lithographic tool which is more compact than current lithographic tools. It is a further object of the invention to provide a method of exerting a force and/or a torque on a movable object.

[0009] According to an aspect of the invention, there is provided a Lorentz type permanent magnet motor comprising: at least one coil assembly arranged in a coil plane defined by a first direction and a second direction perpendicular to the first direction, the at least one coil assembly having multiple coils, each coil comprising two or more main sections extending along the first direction and a turning section transitioning between two adjacent main sections, at least one magnet assembly arranged parallel and proximate to the at least one coil assembly, the at least one magnet assembly having a first magnet group comprising two or more primary magnets extending along the first direction, the two or more primary magnets being placed adjacent to each other along the second direction, the two or more primary magnets having alternating polarization directions, wherein: the at least one magnet assembly further comprises a second magnet group comprising two secondary magnets extending along the second direction, wherein a first secondary magnet is arranged on a first end of the first magnet group and a second secondary magnet is arranged on a second end of the first magnet group, wherein the second end of the first magnet group is opposite to the first end of the first magnet group with respect to the first direction, the secondary magnets of the second magnet group overlap with at least part of the turning section of the at least one coil assembly seen from a third direction which is perpendicular to the first direction, the second direction, and the coil plane.

[00010] According to an aspect of the invention, there is provided a positioning system for positioning a movable object, wherein the positioning system comprises the permanent magnet motor according to any of claims 1 - 12, wherein one of the coil assembly and the magnet assembly is connected to the movable object and the other of the coil assembly and the magnet assembly is connected to an environment.

[00011] According to an aspect of the invention, there is provided a lithographic tool, for example a lithographic apparatus, comprising the positioning system according to claim 13.

[00012] According to an aspect of the invention, there is provided a method of exerting a force and/or a torque on a movable object, the method comprising: providing the permanent magnet motor according to any of claims 1 - 12, the positioning system according to claim 13 or the lithographic tool according to claim 14, connecting one of the coil assembly and the magnet assembly to the movable object and connecting the other of the coil assembly and the magnet assembly to an environment, preferably connecting the magnet assembly to the movable object and the coil assembly to the environment, providing an electric current to the coils of the coil assembly, wherein the electric current provided to each coil of the coil assembly is varied w.r.t. at least one other coil of the coil assembly in order to exert a force or torque on the movable object by interaction of the coil assembly with the magnetic field generated by the magnet assembly, wherein the electric current provided to each coil is dependent on the position of said coil in the coil assembly and a position of the movable object when measured along the second direction.

[00013] According to an aspect of the invention, there is provided a Lorentz type permanent magnet motor comprising: at least one coil assembly arranged in a coil plane defined by a first direction and a second direction perpendicular to the first direction, the at least one coil assembly having multiple coils, at least one magnet assembly arranged parallel and proximate to the at least one coil assembly, comprising two or more magnets extending along the first direction, the two or more primary magnets being placed adjacent to each other along the second direction, the two or more primary magnets having alternating polarization directions, wherein, the coil assembly comprises four or more even number of coils, each controllable for generating a first force in the second direction using a first current component and a second force in a third direction perpendicular to the first and the second direction using a second current component.

BRIEF DESCRIPTION OF THE DRAWINGS

[00014] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a schematic overview of a lithographic apparatus;

Figure 2 depicts a detailed view of a part of the lithographic apparatus of Figure 1 ;

Figure 3 schematically depicts a position control system;

Figure 4 schematically depicts a side view of a prior art permanent magnet motor;

Figure 5 schematically depicts a perspective view of the prior art permanent magnet motor of figure 4;

Figure 6 schematically depicts a perspective view of a first embodiment of a permanent magnet motor according to the invention;

Figure 7 schematically depicts a perspective view of a second embodiment of a permanent magnet motor according to the invention;

Figure 8 schematically depicts a side view of the permanent magnet motor of figure 7 with some parts removed for clarity;

Figure 9 schematically depicts a Halbach array;

Figure 10 schematically depicts a top view of a third embodiment of a permanent magnet motor according to the invention;

Figure 11 schematically depicts a perspective view of the permanent magnet motor of figure 10;

Figure 12 schematically depicts a side view of a fourth embodiment of a permanent magnet motor according to the invention with some parts removed for clarity;

Figure 13 schematically depicts a side view of the permanent magnet motor of figure 12 from a different perspective than in figure 12;

Figure 14 schematically depicts a perspective view of a fifth embodiment of a permanent magnet motor according to the invention;

Figure 15 schematically depicts a top view of a sixth embodiment of a permanent magnet motor according to the invention.

Figure 16 schematically depicts a perspective view of another embodiment of a permanent magnet motor according to the invention.

Figure 17 schematically depicts a perspective view of yet another embodiment of a permanent magnet motor according to the invention. Figure 18 and 19 schematically depict a top and a perspective view of yet another embodiment of a permanent magnet motor according to the invention.

Figure 20 and 21 schematically depict a side and a perspective view of yet another embodiment of a permanent magnet motor according to the invention.

Figure 22 schematically depicts a top view of yet another embodiment of a permanent magnet motor according to the invention.

DETAILED DESCRIPTION

[00015] 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).

[00016] 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.

[00017] 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 a positioning system 31 to position the patterning device MA and a substrate (e.g. a resist coated wafer) W. The positioning system 31 comprises a first positioner PM and a second positioner PW. The first positioner PM is configured to accurately position the patterning device MA in accordance with certain parameters. The mask support MT is connected to the first positioner PM. The second positioner PW is configured to accurately position the substrate support in accordance with certain parameters. The second positioner PW is connected to a substrate support (e.g., a wafer table) WT constructed to hold the substrate W. The lithographic apparatus LA further comprises 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.

[00018] 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. [00019] 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.

[00020] 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.

[00021] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and/or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.

[00022] 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.

[00023] 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 PMS, 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 Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C. [00024] 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.

[00025] 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 vibration isolation 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.

[00026] 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.

[00027] 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.

[00028] 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.

[00029] The position measurement system PMS may comprise an encoder system. An encoder system is known from for example, United States patent application US2007/0058173A1, 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, + l^st order, -1^st order, +2^nd order and -2^nd order. 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 the phase 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 are 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.

[00030] The position measurement system PMS may comprise an interferometer system. An interferometer system is known from, for example, United States patent US6,020,964, filed on luly 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. [00031] 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. [00032] 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 comprises a planar actuator to provide a driving force along multiple axes. For example, the planar actuator may be arranged to move the substrate support WT in 6 degrees of freedom (i.e. move the substrate support WT along the three spatial axes and rotate the substrate support WT around the three spatial axes) . 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.

[00033] 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.

[00034] Figure 4 schematically depicts a side view of a prior art permanent magnet motor 1. Figure 5 schematically depicts this same permanent magnet motor 1 in a perspective view. The permanent magnet motor 1 comprises two coil assemblies 3, i.e. a first coil assembly 27 and a second coil assembly 28, each having multiple coils 7. Systems with a single coil assembly 3 are also known. The permanent magnet motor 1 further comprises a magnet assembly 10.

[00035] The coil assemblies 3 are each arranged in a coil plane 4 which is defined by the first direction 5 and the second direction 6, with the third direction 20 perpendicular to the coil plane 4. The coil plane 4 is a plane which intersects each coil 7 of the coil assembly 3 at a same position relative to an axis of the coil 7. Each coil 7 comprises two main sections 8 extending along the first direction 5 and two turning sections 9 transitioning between two adjacent main sections 8. This is more visible in e.g. figure 10. In figure 10, the turning sections 9 of the coils 7 are visible.

[00036] The magnet assembly 10 of the permanent magnet motor 1 is arranged parallel and proximate to the coil assemblies 3, such that the magnet assembly 10 also lies substantially parallel to the coil plane 4. The magnet assembly 10 comprises a first magnet group 11 comprising multiple primary magnets 12 extending along the first direction 5. The primary magnets 12 are placed adjacent to each other along the second direction 6 and have alternating polarization directions 13. Each primary magnet 12 has an opposite polarization direction than the adjacent primary magnets 12. Halbach arrays (see also figure 9) or other types or magnet arrays with periodic polarization are also known to be used. [00037] Figure 6 schematically depicts a perspective view of a first embodiment of a permanent magnet motor 1 according to the invention. It contains the same components as described above in relation to the prior art permanent magnet motor, with the addition of a second magnet group 14 comprising two secondary magnets 15 extending along the second direction 6. A first secondary magnet 16 is arranged on a first end 17 of the first magnet group 11 and a second secondary magnet 18 is arranged on a second end 19 of the first magnet group 11. The second end 19 of the first magnet group 11 is opposite to the first end 17 of the first magnet group 11 with respect to the first direction 5. Thus, the secondary magnets 15 are arranged perpendicularly to the primary magnets 12 and they preferably extend along all primary magnets 12. The secondary magnets 15 of the second magnet group 14 overlap with at least part of the turning sections 9 of the coil assemblies 3 seen from the third direction 20 which is perpendicular to the first direction 5, the second direction 6, and thus to the coil plane 4. This is better visible in e.g. figure 10.

[00038] Like the prior art permanent magnet motor shown in figures 4 and 5, the permanent magnet motor 1 of figure 6 also comprises two back irons 21 extending in a plane parallel to the coil plane 4. The back irons 21 are arranged adjacent to the coil assemblies 3. The back irons 21 may provide a return path for the magnetic flux, such that the magnetic field in the permanent magnet motor 1 may be strengthened.

[00039] The polarization directions 13 of the primary magnets 12 and of the secondary magnets 15 are oriented along the third direction 20 and each primary magnet 12 has an opposite polarization direction 13 than the adjacent primary magnets 12. However, as discussed above, the primary magnets 12 may alternatively be arranged in a Halbach array (see figure 9). The polarization direction 13 of the first secondary magnet 16 is opposite to the polarization direction 13 of the second secondary magnet 18.

[00040] The second magnet group 14 may allow the permanent magnet motor 1 to provide force not only in the second direction 6, like in prior art permanent magnet motors 1, but also in the first direction 5. Therefore, using multiple motors to allow force application in both in plane directions 5, 6 may no longer be needed, reducing the bulk, weight and complexity of the permanent magnet motor 1. [00041] The permanent magnet motor 1 may be controlled by controlling the current in each of the coils 7 in a three phase system using a current controller. The current in a coil 7 is dependent on at least the position of the coil 7 in the coil assembly and the position of the movable object 32 (e.g. a substrate support WT or a mask support MT, see fig. 1) along the second direction 6, via the following equation: wherein i„ is the current through coil M, I is a common amplitude for all coils, y is the position of the movable object 32 in the second direction 6, s is the spatial period of the primary magnets 12 (i.e. the distance between two magnets 12 of the same polarity 13), and a is a phase angle. The coil number n is counted starting at 1 from a first coil 7, adding 1 for each coil 7 along the second direction 6. It is noted that n = 1 yields the same i„ as n = 4, as the argument of the cosine differs by an amount of 2n and cos((3) = COS(P+2TT). Thus, it follows that there are three distinct current phases, such that this is a three phase system, with the current i„ in each coil 7 varying in phase w.r.t. the neighbouring coils 7 ir over a phase angle of- , i.e. 120 degrees, with each phase split into two subphases for the upper coil part 29 and the lower coil part 30 via the ±a term. Other numbers of phases are also possible, in this f — 1 ~ 1 case, for m phases, the term is replaced by wherein m is an integer. The number of phases depends on the ratio between the distance cs (see fig. 4) between adjacent coils 7 and the spatial period 5 of the primary magnets 12. In the imaged embodiments, the ratio of cs:s is 2:3, i.e. 3 coils 7 over a width of 4 primary magnets 12 (2 of each polarity 13) along the second direction 6 (see e.g. fig. 4), and a 3 phase system is used. If this ratio were e g. 2:5 (5 coils 7 over a width of 4 primary magnets 12), a 5 phase system would be used. If this ratio were e.g. 3:4 (4 coils 7 over a width of 6 primary magnets 12), a 4 phase system would be used, for 2:7, a seven phase system, etcetera. As a general rule, the number of phases preferably equals the smallest integer number of coils that fits in a same width as an integer multiple of the spatial period of the primary magnets v In case of alternating up-down-up-down magnets, this means that the number of phases equals the smallest number of coils that first in a same width as an even integer number of primary magnets, as there are two primary magnets in one spatial period of the primary magnets s . The above is also described in United States patent application US 2018/0224756 Al, which is incorporated herein by reference.

[00042] An upper coil part 29 and a lower coil part 30 have the same coil number n. The phase angle is zero if the coils are not split into an upper coil part 29 and a lower coil part 30. If the coils are split into an upper coil part 29 and a lower coil part 30, the operator + represents an addition for the upper coil part 29 and a subtraction for the lower coil part 30. This, too, is described in US 2018/0224756 Al l and a can be rewritten as wherein F_y is the force exerted by the permanent magnet motor 1 on the movable object 32 in the second direction 6, F_z is the force exerted by the permanent magnet motor 1 on the movable object 32 in the third direction 20, K_y is an actuator constant of the permanent magnet motor for the second direction 6 and K_z is an actuator constant of the permanent magnet motor for the third direction 20. Using this, the current in a coil 7 can be rewritten into two parts, one that determines the driving force exerted by the permanent magnet motor 1 on the movable object 32 with respect to the environment in the second direction 6, and another that determines the levitation force exerted by the permanent magnet motor 1 on the movable object 32 with respect to the environment in the third direction 20. This is derived below. using: cos(A + B) = cos(A)cos(B) — sin(A)sin(A) cos(-A) = cos^A) sin —A) = — sin A') i_y = icos(a) i_z = isin(a) determines the driving force and the sine term determines the levitation force. To provide levitation of the movable object 32, the lower coil part 30 repulses the primary magnets 12 of the first magnet group 11, while the upper coil part attracts the primary magnets 12 of the first magnet group 11. Therefore, the sign of the sine term of the upper coil part 29 is opposite to the sign of the sine term of lower coil part 30.

[00043] Permanent magnet motors 1 using the above control are known from prior art. In the permanent magnet motor 1 according to the invention, the secondary magnets 15 allow the permanent magnet motor 1 to exert a force on the movable object 32 with respect to the environment not only in the second direction 6 and the third direction 20, but also in the first direction 5. This may be done by adding a current component I_x to each of the coil currents, such that:

When I_x is the same for all coils 7 (but may be for example dependent on time or a position of the movable object 32), all coils are attracted by one of the secondary magnets 15 and repulsed by the other of the secondary magnets 15. This results in a force exerted on the movable object 32 with respect to the environment in the first direction 5. I_x may also be varied per coil 7 to achieve other objects. In general, if the distribution of I_x over the coils 7 is symmetric with respect to the center of mass of the movable object 32, the permanent magnet motor 1 can exert a force in the first direction 5 on the movable object 32 with respect to the environment. If the distribution of I_x over the coils 7 is not symmetric with respect to the center of mass of the movable object 32, the permanent magnet motor can exert a torque on the movable object 32 around the third direction 20 with respect to the environment. In this case, it is preferred to use a permanent magnet motor 1 comprising at least two instances of each phase, wherein the coils 7 are split into at least two coil groups 41, 42 such that each coil group 41, 42 comprises all phases (see fig. 15). One I_x may then be applied to the coils 7 of one group 41, 42 of coils 7, while another I_x (for example -I_x) may be applied to the coils 7 of another group 41, 42 of coils 7. All coils 7 in each respective group 41, 42 then get the same /. as the other coils 7 in said respective group 41, 42. This may prevent disturbances in a force exerted onto the movable object 32 by the permanent magnet motor 1 in the second direction 6. This is discussed in more detail in relation to figure 15.

[00044] In the first embodiment of the permanent magnet motor 1 as shown in figure 6, the permanent magnet motor 1 comprises a magnet assembly 10 arranged between two coil assemblies 3, a first coil assembly 27 and a second coil assembly 28. Figure 7 schematically depicts a perspective view of a second embodiment of a permanent magnet motor 1 according to the invention, comprising one coil assembly 3 arranged between two magnet assemblies 10, a first magnet assembly 23 and a second magnet assembly 24.

[00045] The permanent magnet motor 1 according to the invention can be integrated into a positioning system 31, for example a positioning system 31 of a lithographic apparatus LA or another lithographic tool (see figure 1). In such a positioning system 31, one of the coil assembly 3 and the magnet assembly 10 is connected to a movable object 32 such as a substrate support WT or a mask support MT. The other of the of the coil assembly 3 and the magnet assembly 10 is connected to a substantially stationary environment. The permanent magnet motor 1 then can exert a force and/or torque on the movable object 32 with respect to the substantially stationary environment. In the first embodiment as shown in figure 6, preferably the magnet assembly 10 is connected to the movable object 32 while the coil assemblies 3 are connected to a substantially stationary environment. Such an embodiment is called a moving magnet motor. In the second embodiment as shown in figure 7, preferably the coil assembly 3 is connected to the movable object 32 while the magnet assemblies 10 are connected to a substantially stationary environment. Such an embodiment is called a moving coil motor.

[00046] Whether a moving coil motor or a moving magnet motor is preferred depends on the specific application. An advantage of a moving magnet motor may be that the magnets do not need to be connected to any cables or wires for power and cooling. This can reduce the weight and bulk of the moving parts, reducing reaction forces and reaction torques when operating the permanent magnet motor 1. However, in some applications it may be beneficial to use a moving coil motor instead, if it turns out that leads to lighter moving parts due to other design parameters.

[00047] Because the positioning system 31 according to the invention no longer requires separate motors for applying force in both in plane directions 5, 6, the bulk, weight and complexity of the positioning system 31 may be reduced. This may allow a more compact construction of the lithographic apparatus LA and/or may allow more room in the lithographic apparatus LA for other device parts. Furthermore, the reduced weight may allow faster accelerations of the movable object 32 and/or less vibrations, yielding a higher production throughput and/or higher accuracy and/or reduced wear of the lithographic apparatus LA.

[00048] Both the first embodiment of the permanent magnet motor 1 as shown in figure 6 and second embodiment of the permanent magnet motor 1 as shown in figure 7 comprise two back irons 21 , a first back iron 25 and a second back iron 26. In the first embodiment of the permanent magnet motor 1 as shown in figure 6, the first back iron 25 is arranged adjacent to the first coil assembly 27 and the second back iron 26 arranged adjacent to the second coil assembly 28. The coils 7 of the first coil assembly 27 are arranged between the magnet assembly 10 and the first back iron 25, whereas coils 7 of the second coil assembly 28 are arranged between the magnet assembly 10 and the second back iron 26. In the second embodiment of the permanent magnet motor 1 as shown in figure 7, the first back iron 25 is arranged adjacent to the first magnet assembly 23 and the second back iron 26 is arranged adjacent to the second magnet assembly 24. The first magnet group 11 and the second magnet group 14 of the first magnet assembly 23 are arranged between the coil assembly 3 and the first back iron 25, whereas the first magnet group 11 and the second magnet group 14 of the second magnet assembly 24 are arranged between the coil assembly 3 and the second back iron 26.

[00049] Figure 8 schematically depicts a side view of the permanent magnet motor of figure 7 with the second magnet group 14 removed for clarity. In figure 8, the permanent magnet motor 1 is seen from the first direction 5. Each coil 7 is split in a middle of said coil 7 along a split plane 44 parallel to the coil plane 4 into an upper coil part 29 and a lower coil part 30.

[00050] Using the split coils 7, a torque can be exerted on the movable object 32 with respect to the environment by varying the current in the upper coil part 29 in relation to the lower coil part 30 of each coil 7 or a subset of the coils 7.

[00051] A torque can be generated around the first direction by applying a current which causes the upper coil parts 29 to be pulled in the opposite direction along the second direction 6 than the lower coil ( / Tl — 1\ \

2n ( - + ) 1 is modified, e.g. by making i_y different for related upper coil parts 29 and lower coil parts 30. For example:

[00052] Here, in the lower coil part the cosine term has a minus instead of a plus. This way, no net force is exerted in the second direction 6, but a torque is exerted around the first direction 5, as the upper coil part 29 is pulled along the second direction 6 with a force which is equal in magnitude but opposite in sign as a force with which the associated lower coil part 30 is pulled along the second direction 6. Thus, the forces along the second direction 6 are canceled while a torque is generated around the first direction 5.

[00053] Similarly, a torque can be generated around the second direction by applying a current which causes the upper coil parts 29 to be pulled in the opposite direction along the first direction 5 than the lower coil parts 30. To achieve this, the term I_x is modified for related upper coil parts 29 and lower coil parts 30. For example:

[00054] This way, no force is exerted in the first direction 5, but a torque is exerted around the second direction 6.

[00055] The skilled person will recognize that generation of force and torque can be combined simultaneously by addition of current components achieving various goals. For example, a torque can be exerted on the movable object 32 with respect to the environment around the second direction while a force is exerted in the first direction:

[00056] Here, because the term I_x has the opposite sign for the upper and lower coil parts 29, 30 and the term I_X2 has the same sign for the upper and lower coil parts 29, 30, the terms I_xi yield a torque around the second direction 6 while the terms ? yield a force in the first direction 5.

[00057] Figure 9 schematically depicts a first magnet group 11 of a magnet assembly 10 of a permanent magnet motor 1 according to the invention wherein the primary magnets 12 are arranged in a Halbach array 22. In a Halbach array, the polarization directions 13 of the magnets are arranged in a spatially rotating pattern. In the case of the permanent magnet motor 1 according to the present invention, the axis of the rotating pattern in which the polarization directions 13 are arranged extends along the first direction 5. A Halbach array 22 may strengthen the magnetic field inside the permanent magnet motor 1 while reducing the magnetic field outside the permanent magnet motor 1. Other types of periodic polarization magnet arrays (such as sinusoidally varying polarizations 13) may also be used. When a Halbach array 22 or another type of magnet array with a periodic polarization pattern is used, the distance between two primary magnets 12 of equal polarization 13 remains at the same value s as used on the equations and discussion above.

[00058] Figure 10 schematically depicts a top view of a third embodiment of a permanent magnet motor 1 according to the invention. In figure 10, the permanent magnet motor 1 is seen from the third direction 20. Figure 11 schematically depicts a perspective view of the permanent magnet motor 1 of figure 10. In this embodiment, the permanent magnet motor 1 comprises exactly one coil assembly 3 and exactly one magnet assembly 10. A back iron 21 is arranged adjacent to either the coil assembly 3 or the magnet assembly 10. In the imaged embodiment, the back iron is arranged adjacent to the magnet assembly 10, such that the magnet assembly 10 is arranged between the coil assembly 3 and the back iron 21. In the alternative, wherein the back iron 21 is arranged adjacent to the coil assembly 3, the coil assembly 3 is arranged between the magnet assembly 10 and the back iron 21. The back iron 21 may also be omitted. This variant can be seen as a ‘half motor’ variant, seeing that the moving part of the motor is not enclosed by two stationary parts or vice versa.

[00059] Figure 12 schematically depicts a side view of a fourth embodiment of a permanent magnet motor 1 according to the invention with the second magnet group 14 removed for clarity. Figure 13 schematically depicts the same permanent magnet motor 1 as figure 12 from a different perspective, showing also the second magnet group 14 comprising the first secondary magnet 16 and the second secondary magnet 18. In figure 12, the permanent magnet motor 1 is seen from the first direction, whereas in figure 13 , the permanent magnet motor 1 is seen from the second direction 6. The permanent magnet motor 1 according to the fourth embodiment is similar to the permanent magnet motor 1 according to the third embodiment as shown in figures 10 and 11 , in the sense that it is also a half motor design. One difference is that it comprises not one back iron 21 but two back irons 21 and in that in the third embodiment. Another difference is that in the permanent magnet motor 1 according to the third embodiment as shown in figures 10 and 11 the back iron is arranged adjacent to the magnet assembly 10, whereas in the fourth embodiment of the permanent magnet motor 1 according to the invention shown in figures 12 and 13 one of the back irons 21 is arranged adjacent to the coil assembly 3 and the other of the back irons 21 is arranged on the other side of the permanent magnet motor 1.

[00060] Seeing that it may be beneficial to minimize the mass of the moving part of the permanent magnet motor 1 to reduce stress, it may be preferred to use the permanent magnet motor 1 according to the third embodiment as shown in figures 10 and 11 as a moving coil motor, wherein the coil assembly 3 is connected to the movable object 32 such as the substrate support WT or the mask support MT and the magnet assembly 10 is connected to the substantially stationary environment. Similarly, it may be preferred to use the permanent magnet motor 1 according to the fourth embodiment as shown in figures 12 and 13 as a moving magnet motor, wherein the magnet assembly 10 is connected to the movable object 32 such as the substrate support WT or the mask support MT and the coil assembly 3 and the back irons 21 are connected to the substantially stationary environment. [00061] Figure 14 schematically depicts a perspective view of a fifth embodiment of a permanent magnet motor 1 according to the invention. This embodiment is similar to the fourth embodiment as shown in figures 12 and 13 , with the difference that it has no back irons 21. This may further reduce the bulk and weight of the permanent magnet motor 1.

[00062] Figure 15 schematically depicts a perspective view of a sixth embodiment of a permanent magnet motor 1 according to the invention. This embodiment is similar to the fifth embodiment as shown in figure 14, with the difference that it has more coils 7 and more primary magnets 12. The coils 7 are split in a first coil group 41 and a second coil group 42. The first coil group 41 and the second coil group 42 are arranged on opposite sides of a line 43 extending in the first direction 5. Providing a different current to the coils 7 of the first coil group 41 as compared to the coils 7 of the second coil group 42 allows exerting a torque on the movable object 32 around the third direction 20. Specifically, providing a second current component to the first coil group 41 and providing the negative of the second current component to the second coil group 42 may allow exerting a torque around the third direction 20 on the movable object 32, potentially without exerting a further linear force on the movable object 32. This is because in this case, one of the first coil group 41 and the second coil group 42 will be forced upwards (i.e. attracted to the first secondary magnet 16 and repulsed by the second secondary magnet 18) with respect to the magnet assembly 10 and the other of the first coil group 41 and the second coil group 42 will be forced downwards (i.e. attracted to the second secondary magnet 18 and repulsed by the first secondary magnet 16) with respect to the magnet assembly 10 in figure 15.

[00063] Figure 15 shows another embodiment of the permanent magnet motor 1 according to the invention, wherein the coil assembly comprises two coil groups 41 and 42. Due to the interaction of the secondary magnets with the electric currents in each coil, especially i_y, an undesired parasitic moment may be generated around the third direction 20 on the movable object. By applying a second current component +I_X to the coils of the first coil group 41, and the negative of the second current component -I_x to the coils of the second coil group 42, potentially without exerting a further linear force on the movable object. In order to at least partly compensate or cancel the undesired moment around the third direction 20, I_x may be selected to have a magnitude dependent on i_y and the physical dimensions of the coils, for example the coil widths and spaces along the second direction 6, and to have a phase offset with respect to i_y.

[00064] The skilled person will recognize that the core idea of the sixth embodiment of the permanent magnet motor as shown in figure 15, i.e. splitting up the coils 7 into a first coil group 41 and a second coil group 42, can be applied to the other embodiments as well. Preferably, there should in that case be an even number of coils 7, such that both coil groups 41, 42 may have an equal number of coils 7 to provide symmetry. This may aid in providing rotational torque around the third direction 20 without creating an unwanted linear force in the first direction 5 or the second direction 6. It is also feasible and in some cases perhaps preferable that not all coils 7 are used for applying torque around the third direction 20, i.e. that not all coils fall in the first coil group 41 or the second coil group 42. For example, only the outer coils 7 may be used for this. As an example, in figure 15 the second current component may be provided to the leftmost coil only, whereas the negative of the second current component may be provided to the rightmost coil only. In this case, the first coil group 41 comprises only the leftmost coil 7 and the second coil group 42 comprises only the rightmost coil 7. Such specialisation of specific coils 7 in the permanent magnet motor may ease control of the permanent magnet motor 1 as a whole, potentially yielding benefits in hardware connections as well as control logic.

[00065] Figures 16 and 17 schematically show yet another embodiment of the permanent magnet motor 1 according to the invention, wherein the coil assembly 3 comprises four coils 9. Due to the interaction of the primary magnets with the electric currents in each coil, especially z_z, an undesired parasitic moment may be generated around the first direction 5 on the movable object. Figure 16 is similar to the design of Figure 7 and 8 wherein the coil assembly is between two magnet assemblies 10 and Figure 17 is similar to the “half motor” design of Figure 10 and 11 comprising exactly one coil assembly and exactly one magnet assembly. Note that more even number of coils may be comprised in the coil assembly for achieving the same effect, as long as the amplitudes and phases of the coil currents are selected accordingly for generating the desired forces and for at least partly compensating or cancelling the undesired moment around the first direction 5. In this example with four coils, the current phase difference between adjacent coils may be Each of the coils 9, i.e. the nth coil, is controllable and a second force in a third direction perpendicular to the first and the second direction using a second current component l_zn = i_znsin ( \ 2n ( \-S + — 4 — J ) j ). When the second current components are configured R2 R2 such that t_zl = t_z4 = i_z2 * — = <_Z3 * — , the undesired parasitic moment generated around the first direction 5 due to i_zn is at least partly compensated or cancelled. In the equations, R2 is the distance from the center of the two inner coils to the center of the coil assembly, and similarly R1 is the distance from the center of the two outer coils to the center of the coil assembly. The coils 9 may be split into an upper part and a lower part along a split plane parallel to the coil plane, the currents of the upper part and the lower part may be controlled separately, having for example opposite second current components, i.e. I_zn_i_ower ⁼ ~Izn_upper ^such that the undesired parasitic moment generated on the movable object due to i_zn around the first direction 5 is at least partly compensated or cancelled.

[00066] Figure 18 and Figure 19 show yet another embodiment of a permanent magnet motor 1 according to the invention. In this embodiment the permanent magnet motor 1 comprise a coil assembly 3 arranged in a coil plane defined by a first direction 5 and a second direction 6 perpendicular to the first direction, the coil assembly 3 having multiple coils 9. The permanent magnet motor 1 further comprises a magnet assembly 10 arranged parallel and proximate to the coil assembly, comprising two or more magnets extending along the first direction, the two or more magnets being placed adjacent to each other along the second direction 6, the two or more primary magnets having alternating polarization directions. The coil assembly 3 comprises four or more even number of adjacent coils 9, each controllable for generating a first force in the second direction 6 using a first current component and a second force in a third direction 20 perpendicular to the first and the second direction using a second current component. Similar to the previous embodiment, when the second current components

R2 R2 are configured such that t_zl = i_z4 = i_z2 * — = i_z3 * the undesired parasitic moment generated on the movable object due to i_zn around the first direction 5 is at least partly compensated or cancelled.

[00067] Figure 18 and Figure 19 show the embodiment according to a “half motor” design comprising exactly one coil assembly and exactly one magnet assembly. While in Figure 20 and 21, another embodiment is shown having a coil assembly 3 between two magnet assemblies 10. In this embodiment, each coil is split in a middle of said coil along a split plane 44 parallel to the coil plane 4 into an upper coil part 29 and a lower coil part 30, allowing to be separately controlled. Similarly, when the second current components of the coils are configured as

The undesired parasitic moment generated on the movable object due to i_zn around the first direction 5 may be at least partly compensated or cancelled. Note that Figure 18 and 19 is showing a moving coil motor configuration, and it should be understood that a moving magnet motor would work similarly. [00068] It should be understood that two or more of the permanent magnet motor designs in the embodiments can be combined to achieve more flexibilities in actuating the movable object. For example in an embodiment as shown in Figure 22, four such motors, Motor 1, 2, 3, 4, are disposed as a 2-by-2 matrix. By separately controlling the current components of the coils in the coil assemblies, linear forces in the first, second, third direction and torques around the first, second, third directions may be generated, and moments around the directions may be at least partly compensated or cancelled. It should be understood that the design of each of the motors, the number of motors combined, and the manner of disposing the motors may be chosen otherwise for intended purposes and applications.

[00069] 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.

[00070] 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.

[00071] 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.

[00072] Other aspects of the invention are set-out as in the following numbered clauses.

1. A Lorentz type permanent magnet motor comprising: at least one coil assembly arranged in a coil plane defined by a first direction and a second direction perpendicular to the first direction, the at least one coil assembly having multiple coils, each coil comprising two or more main sections extending along the first direction and a turning section transitioning between two adjacent main sections, at least one magnet assembly arranged parallel and proximate to the at least one coil assembly, the at least one magnet assembly having a first magnet group comprising two or more primary magnets extending along the first direction, the two or more primary magnets being placed adjacent to each other along the second direction, the two or more primary magnets having alternating polarization directions, wherein: the at least one magnet assembly further comprises a second magnet group comprising two secondary magnets extending along the second direction, wherein a first secondary magnet is arranged on a first end of the first magnet group and a second secondary magnet is arranged on a second end of the first magnet group, wherein the second end of the first magnet group is opposite to the first end of the first magnet group with respect to the first direction, the secondary magnets of the second magnet group overlap with at least part of the turning section of the at least one coil assembly seen from a third direction which is perpendicular to the first direction, the second direction, and the coil plane.

2. The permanent magnet motor according to clause 1, further comprising a back iron extending in a plane parallel to the coil plane, wherein the back iron is arranged adjacent to the at least one coil assembly or the at least one magnet assembly.

3. The permanent magnet motor according to clause 1 or 2, wherein the polarization directions of the primary magnets and/or of the secondary magnets are oriented along the third direction.

4. The permanent magnet motor according to any of clauses 1 - 3, wherein the polarization direction of the first secondary magnet is opposite to the polarization direction of the second secondary magnet. The permanent magnet motor according to any of clauses 1 - 4, wherein each primary magnet has a different polarization direction than at least one adjacent primary magnet, wherein preferably the two or more primary magnets are arranged in a Halbach array. The permanent magnet motor according to any of clauses 1 - 4, wherein each primary magnet has an opposite polarization direction than at least one adjacent primary magnet. The permanent magnet motor according to any of clauses 1 - 6, wherein the coil assembly is arranged between two magnet assemblies, the two magnet assemblies comprising a first magnet assembly and a second magnet assembly. The permanent magnet motor according to clause 7, wherein: the permanent magnet motor comprises a first back iron arranged adjacent to the first magnet assembly and a second back iron arranged adjacent to the second magnet assembly, the first magnet group and the second magnet group of the first magnet assembly are arranged between the coil assembly and the first back iron, the first magnet group and the second magnet group of the second magnet assembly are arranged between the coil assembly and the second back iron. The permanent magnet motor according to any of clauses 1 - 6, comprising a magnet assembly arranged between two coil assemblies, the two coil assemblies comprising a first coil assembly and a second coil assembly. The permanent magnet motor according to clause 9, wherein: the permanent magnet motor comprises a first back iron arranged adjacent to the first coil assembly and a second back iron arranged adjacent to the second coil assembly, at least one coil of the first coil assembly is arranged between the magnet assembly and the first back iron, at least one coil of the second coil assembly is arranged between the magnet assembly and the second back iron. The permanent magnet motor according to any of clauses 1 - 6, comprising exactly one coil assembly and exactly one magnet assembly, wherein: the magnet assembly is arranged between the coil assembly and the back iron, wherein the back iron is arranged adjacent to the magnet assembly, or the coil assembly is arranged between the magnet assembly and the back iron, wherein the back iron is arranged adjacent to the coil assembly. The permanent magnet motor according to any of clauses 1 - 11, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part. The permanent magnet motor according to any of clauses 1-12, wherein the coil assembly comprises four or more even number of coils, each controllable to generate a first force in the second direction using a first current component and a second force in a third direction perpendicular to the first and the second direction using a second current component, wherein the second current components of at least two of the coils differ in amplitude for at least partly compensating or cancelling a moment around the first direction. A positioning system for positioning a movable object, wherein the positioning system comprises the permanent magnet motor according to any of clauses 1 - 13, wherein one of the coil assembly and the magnet assembly is connected to the movable object and the other of the coil assembly and the magnet assembly is connected to an environment. A lithographic tool, for example a lithographic apparatus, comprising the positioning system according to clause 14. A method of exerting a force and/or a torque on a movable object, the method comprising: providing the permanent magnet motor according to any of clauses 1 - 13, the positioning system according to clause 14 or the lithographic tool according to clause 15, connecting one of the coil assembly and the magnet assembly to the movable object and connecting the other of the coil assembly and the magnet assembly to an environment, preferably connecting the magnet assembly to the movable object and the coil assembly to the environment, providing an electric current to the coils of the coil assembly, wherein the electric current provided to each coil of the coil assembly is varied w.r.t. at least one other coil of the coil assembly in order to exert a force or torque on the movable object by interaction of the coil assembly with the magnetic field generated by the magnet assembly, wherein the electric current provided to each coil is dependent on the position of said coil in the coil assembly and a position of the movable object when measured along the second direction. The method according to clause 16, wherein the electric current provided to each coil of the coil assembly includes a first current component equal for each coil of the coil assembly, in order to exert a force on the movable object in the first direction. The method according to clauses 16 or 17, comprising the step of providing a second current component to a first coil group and providing the negative of the second current component to a second coil group, wherein the first coil group and the second coil group are arranged on opposite sides of a line extending in the first direction, in order to exert a torque or at least partly compensate or cancel a moment on the movable object around the third direction. The method according to any of clauses 16 - 18, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part, the method comprising controlling a relation between a current provided to each upper coil part as compared to a current provided to its corresponding lower coil part in order to: exert a torque on the movable object around the first direction, and/or exert a torque on the movable object around the second direction. A Lorentz type permanent magnet motor comprising: at least one coil assembly arranged in a coil plane defined by a first direction and a second direction perpendicular to the first direction, the at least one coil assembly having multiple coils, at least one magnet assembly arranged parallel and proximate to the at least one coil assembly, comprising two or more magnets extending along the first direction, the two or more primary magnets being placed adj acent to each other along the second direction, the two or more primary magnets having alternating polarization directions, wherein, the coil assembly comprises four or more even number of coils, each controllable for generating a first force in the second direction using a first current component and a second force in a third direction perpendicular to the first and the second direction using a second current component.

21. The permanent magnet motor according to clause 20, comprising exactly one coil assembly and exactly one magnet assembly, wherein: the magnet assembly is arranged between the coil assembly and the back iron, wherein the back iron is arranged adjacent to the magnet assembly, or the coil assembly is arranged between the magnet assembly and the back iron, wherein the back iron is arranged adjacent to the coil assembly.

22. The permanent magnet motor according to clause 20, wherein the coil assembly is arranged between two magnet assemblies.

23. The permanent magnet motor according to clause 22, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part.

24. The permanent magnet motor according to any of clauses 20 - 23, wherein the second current components of at least two of the coils have different amplitudes for at least partly compensating or cancelling a parasitic moment around the first direction.

25. The permanent magnet motor according to any of clauses 20-24, wherein the different amplitudes have a linear relationship dependent on the dimensions of the coil assembly.

26. A lithographic tool, for example a lithographic apparatus, comprising the permanent magnet motor according to any of clauses 20 - 25.

27. A method of exerting on a movable object a first force in a second direction and a second force in a third direction perpendicular to the first and a second direction, the method comprising: providing the permanent magnet motor according to any of clauses 20 - 25, or the lithographic tool according to clause 26, connecting one of the coil assembly and the magnet assembly to the movable object and connecting the other of the coil assembly and the magnet assembly to an environment, providing to each coil of the coil assembly a first current component for generating a first force in the second direction, and a second current component for generating a second force in the third direction, wherein the second current components of at least two of the coils have different amplitudes for at least partly compensating or cancelling a parasitic moment around the first direction. 28. The method according to clause 27, wherein the amplitudes have a linear relationship dependent on the dimensions of the coil assembly.

[00073] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

2. The permanent magnet motor according to claim 1, further comprising a back iron extending in a plane parallel to the coil plane, wherein the back iron is arranged adjacent to the at least one coil assembly or the at least one magnet assembly.

3. The permanent magnet motor according to claim 1 or 2, wherein the polarization directions of the primary magnets and/or of the secondary magnets are oriented along the third direction.

4. The permanent magnet motor according to any of claims 1 - 3, wherein the polarization direction of the first secondary magnet is opposite to the polarization direction of the second secondary magnet.

5. The permanent magnet motor according to any of claims 1 - 4, wherein the coil assembly is arranged between two magnet assemblies, the two magnet assemblies comprising a first magnet assembly and a second magnet assembly.

6. The permanent magnet motor according to any of claims 1 - 4, comprising a magnet assembly arranged between two coil assemblies, the two coil assemblies comprising a first coil assembly and a second coil assembly.

7. The permanent magnet motor according to any of claims 1 - 4, comprising exactly one coil assembly and exactly one magnet assembly, wherein: the magnet assembly is arranged between the coil assembly and the back iron, wherein the back iron is arranged adjacent to the magnet assembly, or the coil assembly is arranged between the magnet assembly and the back iron, wherein the back iron is arranged adjacent to the coil assembly.

8. The permanent magnet motor according to any of claims 1 - 7, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part.

9. The permanent magnet motor according to any of claims 1-8, wherein the coil assembly comprises four or more even number of coils, each controllable to generate a first force in the second direction using a first current component and a second force in a third direction perpendicular to the first and the second direction using a second current component, wherein the second current components of at least two of the coils differ in amplitude for at least partly compensating or cancelling a moment around the first direction.

10. A positioning system comprising the permanent magnet motor according to any of claims 1-9 and a current controller, wherein the permanent magnet motor comprises a first coil group and a second coil group arranged on opposite sides of a line extending in the first direction, the current controller is configured to be able to provide a second current component to the first coil group and the negative of the second current component to the second coil group, in order to exert a torque or at least partly compensate or cancel a moment on the movable object around the third direction.

11. A lithographic tool, for example a lithographic apparatus, comprising the positioning system according to claim 10.

12. A method of exerting a force and/or a torque on a movable object, the method comprising: providing the permanent magnet motor according to any of claims 1 - 9, the positioning system according to claim 10, or the lithographic tool according to claim 11, connecting one of the coil assembly and the magnet assembly to the movable object and connecting the other of the coil assembly and the magnet assembly to an environment, preferably connecting the magnet assembly to the movable object and the coil assembly to the environment, providing an electric current to the coils of the coil assembly, wherein the electric current provided to each coil of the coil assembly is varied w.r.t. at least one other coil of the coil assembly in order to exert a force or torque on the movable object by interaction of the coil assembly with the magnetic field generated by the magnet assembly, wherein the electric current provided to each coil is dependent on the position of said coil in the coil assembly and a position of the movable object when measured along the second direction.

13. The method according to claim 12, wherein the electric current provided to each coil of the coil assembly includes a first current component equal for each coil of the coil assembly, in order to exert a force on the movable object in the first direction.

14. The method according to claims 12 or 13, comprising the step of providing a second current component to a first coil group and providing the negative of the second current component to a second coil group, wherein the first coil group and the second coil group are arranged on opposite sides of a line extending in the first direction, in order to exert atorque or at least partly compensate or cancel a moment on the movable object around the third direction.

15. The method according to any of claims 12 - 14, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part, the method comprising controlling a relation between a current provided to each upper coil part as compared to a current provided to its corresponding lower coil part in order to: exert a torque on the movable object around the first direction, and/or exert a torque on the movable object around the second direction.

16. A Lorentz type permanent magnet motor comprising: at least one coil assembly arranged in a coil plane defined by a first direction and a second direction perpendicular to the first direction, the at least one coil assembly having multiple coils, at least one magnet assembly arranged parallel and proximate to the at least one coil assembly, comprising two or more magnets extending along the first direction, the two or more primary magnets being placed adjacent to each other along the second direction, the two or more primary magnets having alternating polarization directions, wherein, the coil assembly comprises four or more even number of coils, each controllable for generating a first force in the second direction using a first current component and a second force in a third direction perpendicular to the first and the second direction using a second current component.

17. The permanent magnet motor according to claim 16, comprising exactly one coil assembly and exactly one magnet assembly, wherein: the magnet assembly is arranged between the coil assembly and the back iron, wherein the back iron is arranged adjacent to the magnet assembly, or the coil assembly is arranged between the magnet assembly and the back iron, wherein the back iron is arranged adjacent to the coil assembly.

18. The permanent magnet motor according to claim 16, wherein the coil assembly is arranged between two magnet assemblies.

19. The permanent magnet motor according to claim 18, wherein each coil is split in a middle of said coil along a split plane parallel to the coil plane into an upper coil part and a lower coil part.

20. The permanent magnet motor according to any of claims 16 - 19, wherein the second current components of at least two of the coils have different amplitudes for at least partly compensating or cancelling a parasitic moment around the first direction.

21. The permanent magnet motor according to any of claims 16 - 20, wherein the different amplitudes have a linear relationship dependent on the dimensions of the coil assembly.

22. A lithographic tool, for example a lithographic apparatus, comprising the permanent magnet motor according to any of claim 16 - 21.

23. A method of exerting on a movable object a first force in a second direction and a second force in a third direction perpendicular to the first and a second direction, the method comprising: providing the permanent magnet motor according to any of claims 16 - 21, or the lithographic tool according to claim 22, connecting one of the coil assembly and the magnet assembly to the movable object and connecting the other of the coil assembly and the magnet assembly to an environment, providing to each coil of the coil assembly a first current component for generating a first force in the second direction, and a second current component for generating a second force in the third direction, wherein the second current components of at least two of the coils have different amplitudes for at least partly compensating or cancelling a parasitic moment around the first direction.

24. The method according to claim 23, wherein the amplitudes have a linear relationship dependent on the dimensions of the coil assembly.