CROSS-REFERENCE TO RELATED APPLICATION

[0001] The application claims priority of EP application 22206830.6 which was filed on 11 November, 2022 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a linear motor motion system, a lithographic apparatus comprising such a linear motor motion system, and a method of driving a linear motor motion system.

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] Linear motor motion systems may be used in different subsystems of a lithographic apparatus. For example, a linear motor motion system may be used in a substrate table and in a support that supports a patterning device, such as a mask table. The linear motor motion systems may comprise a magnetic track and a plurality of coils comprised in a coil unit. The coils are guided along the magnetic track. A commutation device provides sine shaped signals to the coils, e.g. as a function of a position of the coils in respect of the magnetic track to generate a motor force between the coils and the magnetic track. A bearing, such as an air bearing may be used to guide the coils along the magnetic track.

[0006] Movement of the coils of the linear motor motion system in respect of the magnetic track may result in vibrations or other disturbances. SUMMARY

[0007] Considering the above, it is an object of the invention to provide an operation of a linear motor motion system with a low amount of vibrations or other disturbances.

[0008] According to an embodiment of the invention, there is provided a linear motor motion system configured to move an object, the linear motor motion system comprising: a magnetic track; a coil unit, including a plurality of coils wound about respective ferromagnetic cores, a bearing configured to guide the coil unit along the magnetic track, wherein the bearing is constructed and arranged to only allow substantial movement of the coil unit relative to the magnetic track in a first direction; a commutation device configured to provide input signals to each of the coils, wherein the commutation device is configured to provide the input signals to generate an actuation force in the first direction to move the object in the first direction and a compensation force in a second direction perpendicular to the first direction to at least partly compensate a disturbance force in the second direction.

[0009] According to a further embodiment of the invention, there is provided a lithographic apparatus comprising the linear motor motion system according to the invention.

[00010] According to a yet further embodiment of the invention, there is provided a method of driving a linear motor motion system, the linear motor motion system comprising: a magnetic track; a coil unit, including a plurality of coils wound about respective ferromagnetic cores, a bearing configured to guide the coil unit along the magnetic track, wherein the bearing is constructed and arranged to only allow substantial movement of the coil unit relative to the magnetic track in a first direction; the method comprising providing input signals to each of the coils, wherein the input signals are provided to generate an actuation force in the first direction to move the object in the first direction and a compensation force in a second direction perpendicular to the first direction to at least partly compensate a disturbance force in the second direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[00011] 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 an embodiment of the invention may be employed;

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

Figure 3 schematically depicts a position control system as part of a positioning system as may be used with an embodiment of the invention; Figure 4A depicts a schematic view of a linear motor motion system according to an embodiment of the invention;

Figure 4B depicts a graph of a disturbance force in the linear motor motion system according to Figure 4A;

Figure 5 depicts a schematic, detailed view of a part of the linear motor motion system according to Figure 4A;

Figure 6 depicts a perspective view of a linear motor motion system according to Figure 4A.. . Figure 7 depicts a graphic view of a disturbance force and a compensation force according to an embodiment of the invention; and

Figure 8 depicts a block schematic view of the commutation device of the linear motor motion system according to an embodiment of the invention.

DETAILED DESCRIPTION

[00012] 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).

[00013] 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.

[00014] 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.

[00015] 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.

[00016] 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.

[00017] 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.

[00018] 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. [00019] 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.

[00020] 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 Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[00021] 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.

[00022] 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.

[00023] 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.

[00024] 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.

[00025] 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.

[00026] 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 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.

[00027] 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 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. [00028] 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 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 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.

[00029] The first positioner PM and the second positioner PW each are provided with an actuator to move respectively the mask support MT and the substrate support WT. The actuator may be a linear actuator to provide a driving force along a single axis, for example the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axis. The actuator may be a planar actuator to provide a driving force along multiple axis. For example, the planar actuator may be arranged to move the substrate support WT in 6 degrees of freedom. The actuator may be an electromagnetic 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.

[00030] 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.

[00031] In a lithographic apparatus, use may be made of plural linear motor motion systems. For example, a linear motor motion system may be configured to position the substrate support WT. As an example a linear motor motion system may be provided that is configured to position the long stroke of the substrate support. As another example, two linear motor motion systems may be configured to position the long stroke of the substrate support, namely one linear motor motion system to move the substrate support in an X direction and one linear motor motion system to move the substrate support in an Y direction, whereby the X and Y directions are perpendicular and span a horizontal plane. As another example, the lithographic apparatus may be a dual stage or multiple stage lithographic apparatus. In such “dual stage” or “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. As yet another example of linear motion motor systems, the lithographic apparatus comprises at least one linear motor motion system that is configured to position the substrate support and at least one linear motor motion system that is configured to position the support that supports the patterning device.

[00032] The linear motor motion systems may comprise a magnetic track and a coil unit comprising a plurality of coils. A commutation device provides sine shaped signals to the coils, e.g. as a function of a position of the coils in respect of the magnetic track to generate a motor force between the coils and the magnetic track. The coil unit comprising the coils is guided along the magnetic track. A bearing, such as an air bearing may be used to guide the coil unit along the magnetic track.

[00033] In the linear motor motion system, the magnetic track may be stationary, i.e. connected to a stationary structure, while the coils may be connected to a movable structure in order to be able to exert a motor force onto the movable structure. As an alternative, the coils may be stationary, i.e. connected to a stationary structure, while the magnetic track may be connected to a movable structure in order to be able to exert a motor force onto the movable structure.

[00034] A movement by one of the linear motion control system may result in a disturbance force, causing e.g. vibrations, that affect other parts of the lithographic apparatus. For example, in a dual stage system, a movement of one of the stages by a linear motor motion system may result in vibrations that may affect the other one of the stages. As a result, the other one of the stages may be subject to vibrations which may adversely affect a positioning accuracy of the other one of the stages. [00035] A bearing may be comprised in the linear motor motion system and be configured to guide the coils in respect of the magnetic track. The bearing may for example comprise an air bearing. The air bearing may assist to suppress vibrations caused by a movement by the linear motor motion system. Firstly, the air bearing may exhibit a compliancy which may promote a suppression of vibrations in the linear motor motion system in which the vibration may be generated. Secondly, the air bearing of another linear motor motion system, subject to incoming vibrations, i.e. vibrations from other sources, may tend to suppress such vibrations via the linear motor motion system by the compliancy of the air bearing thereof.

[00036] In general, the requirement specification imposed on a lithographic apparatus tend to be raised over time. For example, a maximum of the overlay error tends to be lowered over time in order to reduce a line width of the patterns to be irradiated onto the substrate. As another example, a scanning velocity with which the substrate is moved by the lithographic apparatus, tends to be increased over time in order to increase a throughput of the lithographic apparatus.

[00037] In view of the raise of requirements, the linear motor motions systems tend to be faced with more stringent requirements: on the one hand, motor force, acceleration tends to be raised while on the other hand, a highly accurate positioning of e.g. the substrate table is required.

[00038] In view of the raising requirements, the inventors have devised that the linear motor motion system may form a source of vibration during movement of the linear motor motion system.

[00039] In particular, the inventors have devised that the linear motor motion system may generate vibrations associated with the periodic, repetitive structure of the magnetic track. The inventors have observed that the movement of a linear motor motion system in a lithographic apparatus may form a source of vibration, whereby a frequency content of the vibration appeared to associate with a velocity of movement of the linear motor motion system.

[00040] Figure 4A depicts a highly schematic side view of a linear motor motion system. The linear motor motion system comprises a magnetic track MT which comprises a linearly extending array of magnets. The magnets alternate in a magnetic polarity thereof, resulting in a magnetic field MF which alternates in polarity thereof, magnetic field lines extending from each of magnetic N poles of the magnetic track to neighboring S poles of the magnetic track. The linear motor motion system further comprises a coil unit CLU comprising in this example 3 coils, which are schematically indicated by windings of the coils R, S and T. A distance between the coil windings of coils R and S is indicated by Pl and a distance between the coil windings of coils R and T is indicated by P2. The linear motor motion system further comprises a commutation device COM which provides input signals to each of the coils R, S, T of the coil unit CLU. The commutation device provides the input signals to the coils, for example in response to a setpoint signal, which setpoint signal may comprise a position setpoint of the linear motor motion system, a force setpoint of the linear motor motion system or a position setpoint and a force setpoint of the linear motor motion system. As a further example, the commutation device may provide the input signals to the coils in response to an actual position of the linear motor motion system, such as a measured position of the linear motor motion system. The measured position of the linear motor motion system may be obtained from a measured position of the object. The linear motor motion system comprises a bearing which is constructed and arranged to only allow substantial movement of the coil unit relative to the magnetic track in a first direction indicated by the arrow X in Figure 4B. In the present embodiment, the bearing is schematically indicated by an air bearing AB between the coil unit CLU and the magnetic track MT, the air bearing may make use of any suitable gas or gas mixture between the coil unit and the magnetic track, such as nitrogen or synthetic air.

[00041] The linear motor motion system is configured to position an object OBJ. In the present example, the object is connected to the coil unit CLU so as to be moved by a movement of the coil unit in respect of the magnetic track.

[00042] Figure 5 depicts a view of the magnetic track MT whereby the direction of the alternating direction of the magnetic field MF is illustrated, the alternation in the first direction X as indicated in Figure 4A. The magnetic track MT comprises a back iron BLMT arranged at a side of the magnets facing away from the coils of the coil unit.

[00043] Figure 6 depicts a perspective view of parts of a linear motor motion system and shows the magnetic track MT extending in the first direction X, the magnetic track comprising the back iron BIMT and the plurality of magnets with alternate magnetic polarity. The coil unit CLU comprising the plurality of coils and an iron core IC-CLU, is arranged on the magnetic track and movable, by the bearing (not shown in Figure 6), in the first direction X.

[00044] As will be understood from the alternating magnetic field as depicted in Figure 5, as the coil unit moves along the magnetic track, the magnetic polarity of the magnetic field changes. The commutation device provides the signals to the coils in accordance with the spatially changing magnetic field directions.

[00045] The magnetic field also changes in the vertical direction, as depicted in Figure 4B, showing a schematic representation of the magnetic field strength in the vertical direction, also identified as the Z direction in Figure 6. As follows from Figure 4B, the magnetic field strength in the vertical direction alternates between a positive and a negative value, seen along the first direction X.

[00046] The inventors have realized that a disturbance force may occur as the coil unit moves through the magnetic field with alternating polarity, which disturbance force may result in a vibration, and that this disturbance force may at least partly be compensated by the commutation device, as will be explained in the below.

[00047] Figure 7 depicts, along the vertical axis, the disturbance force DF in the vertical (second) direction, and along the horizontal axis the position of the coil unit in respect of the magnetic track seen in the first direction X. As follows from figure 8, the disturbance force exhibits a periodicity along the first direction X. According to the invention, the commutation device is configured to provide the signals to the coils to at least partly compensate the disturbance force. The commutation device is configured to provide the input signals to the coils to generate a compensation force CF which at least partly compensates the disturbance force. It is noted that in Figure 7, the disturbance force and the compensation force are depicted with a same polarity for illustrative purpose. It will be understood that, in order to compensate the disturbance force, the polarity of the compensation force may in practice be opposite to the polarity of the disturbance force in order for the forces to at least partly compensate each other.

[00048] In an embodiment, the commutation device comprises a disturbance force profile as a function of a position in the first direction. The disturbance force profile may be based on a modelling of the linear motor motion system or on measurement of the vertical force. As the disturbance force profile is a function of the position of the coil unit in respect of the magnetic track in the first direction, the alternating character of the disturbance force may be modelled accurately, enabling to accurately determine a compensation force as may be required to compensate the disturbance force. The position in the first direction may be provided by the setpoint signal comprising a position setpoint of the linear motor motion system in the first direction. Alternatively, the position in the first direction is obtained from a position measurement, e.g. by an encoder or interferometer, which provides e.g. a position of the object positioned by the linear motor motion system.

[00049] In an embodiment, the disturbance force profile comprises four (4) sine functions dependent on the position in the first direction. As seen in figure 7, the periodic character of the disturbance force appears to show a base spatial frequency and higher harmonics of the base spatial frequency. Such a wave form may be accurately modelled with plural sine functions dependent of the position in the first direction. As described above, the position in the first direction may be provided by the setpoint signal comprising a position setpoint of the linear motor motion system in the first direction. Alternatively, the position in the first direction is obtained from a position measurement, e.g. by an encoder or interferometer, which provides e.g. a position of the object positioned by the linear motor motion system.

[00050] In an embodiment, based on the disturbance force profile and the position of the coil unit in respect of the magnetic track in the first direction, the commutation device is configured to generate a disturbance force signal using the disturbance force profile and the position in the first direction. The disturbance force signal accordingly provides an indication of the disturbance force at the momentary position of the coil unit in respect of the magnetic track. The commutation device may determine the desired compensation force using the disturbance force signal.

[00051] The disturbance force has been observed to be not only dependent on a position of the coil unit in respect of the magnetic track. Rather, the disturbance force has been determined to further be dependent on a motor current: the larger the motor current in the coil unit, the higher the motor force in the first direction. However , the higher the motor current, the higher the disturbance force appears to be. However, the motor current may also depend on the amount of compensation that may be required to compensate the disturbance force. Thus, in fact, the required compensation force, being motor current dependent, could only be determined when the motor current is known, while the motor current can only be determined once the required compensation force is known. The inventors have addressed this dependency by using the determined actuation force signal in the first direction as an approximation indicative of the motor current. Thereby, the dependency on the motor current may be taken into account by scaling the disturbance force signal by an actuation force signal representative of the setpoint force in the first direction. Accordingly, in an embodiment, the commutation device is configured to determine an actuation force signal from the setpoint signal, the actuation force signal representing a force by the linear motor in the first direction, to scale the disturbance force signal by the actuation force signal to determine a compensation force signal, and to derive the input signals as provided to each of the coils using the actuation force signal and the compensation force signal.

[00052] The disturbance force may be in the direction perpendicular to the direction of movement of the linear motor motion system. In an embodiment, the disturbance force comprises a linear motor disturbance force in the second direction which is perpendicular to the first direction and perpendicular to a surface of the magnetic track. Thereby, the first direction may be a horizontal direction and the second direction may be a vertical direction.

[00053] Figure 8 provides a schematic view based on which an embodiment of an operation of the commutation device will be explained. A setpoint PSET is provided to the commutation device. Using 4 sine functions, SIN1, SIN2, SIN3, SIN4 which are comprised in the disturbance force profile DFP, a disturbance force signal DSFS is determined. Instead of a position setpoint, a position signal representing a measured position of the linear motor motion system may be provided.

[00054] A linear motor motion system force setpoint FSET is provided to the linear motor motion system. Using the linear motor motion system force setpoint and the position setpoint, a motor cogging effect is taken into account by the actuation force controller AFC, outputting an actuation force signal AFS. The actuation force signal AFS and the disturbance force signal DSFS are provided to a scaler SCE which scales the disturbance force signal DSFS by the actuation force signal AFS to provide the compensation force signal CFS. As explained above, the actuation force signal AFS is thereby used as an indication of the linear motor motion system motor current to scale the disturbance force signal DSFS. The actuation force signal AFS and the compensation force signal CFS are provided to a coil commutation device CCD which determines the input signals CIS to each of the coils S, R, T.

[00055] The lithographic apparatus according to the invention comprises the linear motor motion system according as described above. The linear motor motion system may be configured to position an object of the lithographic apparatus. In an embodiment, the object is one of a substrate stage, such as a substrate support (e.g., a wafer table) WT, and a mask stage, such as a mask support (e.g., a mask table), of the lithographic apparatus.

[00056] For example, the linear motor motion system may be configured to position the substrate support WT. As an example a linear motor motion system may be configured to position the long stroke of the substrate support. As another example, the lithographic apparatus may be a dual stage lithographic apparatus, comprising a linear motor motion system for positioning the substrate support of the first stage (e.g. a metrology stage) and a linear motor motion system for positioning the substrate support of the second stage (e.g. an expose stage). A disturbance force due to a movement of the linear motor motion system for positioning the substrate support of the first stage may at least partly be compensated as described above, to at least reduce an effect of the disturbance force on the positioning of the substrate support of the second stage. As yet another example of linear motion motor systems, the lithographic apparatus comprises at least one linear motor motion system that is configured to position the substrate support and at least one linear motor motion system that is configured to position the support that supports the patterning device. Similarly, a disturbance force due to a movement of the linear motor motion system for positioning the patterning device may at least partly be compensated as described above, to at least reduce an effect of the disturbance force on the positioning of the substrate support. Also, a disturbance force due to a movement of the linear motor motion system for positioning the substrate support may at least partly be compensated as described above, to at least reduce an effect of the disturbance force on the positioning of the patterning device.

[00057] 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.

[00058] 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.

[00059] 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, optical or electron-beam metrology, particle or electron-beam lithography.

[00060] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine -readable medium, which may be read and executed by one or more processors. A machine -readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and 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.

[00061] 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. A linear motor motion system configured to move an object, the linear motor motion system comprising: a magnetic track; a coil unit, including a plurality of coils wound about respective ferromagnetic cores, a bearing configured to guide the coil unit along the magnetic track, wherein the bearing is constructed and arranged to only allow substantial movement of the coil unit relative to the magnetic track in a first direction; a commutation device configured to provide input signals to each of the coils, wherein the commutation device is configured to provide the input signals to generate an actuation force in the first direction to move the object in the first direction and a compensation force in a second direction perpendicular to the first direction to at least partly compensate a disturbance force in the second direction.

2. The linear motor motion system according to clause 1, wherein the commutation device comprises a disturbance force profile as a function of a position in the first direction.

3. The linear motor motion system according to clause 2, wherein the disturbance force profile comprises 4 sine functions dependent on the position in the first direction.

4. The linear motor motion system according to clause 2 or 3, wherein the commutation device is configured to generate a disturbance force signal using the disturbance force profile and the position in the first direction.

5. The linear motor motion system according to clause 4, wherein the commutation device is configured to determine an actuation force signal from a setpoint signal of the linear motor motion system, the actuation force signal representing a force by the linear motor in the first direction, to scale the disturbance force signal by the actuation force signal to determine a compensation force signal, and to derive the input signals as provided to each of the coils using the actuation force signal and the compensation force signal. 6. The linear motor motion system according to any one of the preceding clauses, wherein the commutation device is configured to determine the position in the first direction from one of the setpoint signal of the linear motor motion system and a position measurement signal representing a measured position of the linear motor motion system.

7. The linear motor motion system according to any one of the preceding clauses, wherein the disturbance force comprises a linear motor disturbance force in the second direction.

8. The linear motor motion system according to any one of the preceding clauses, wherein the first direction is a horizontal direction and the second direction is a vertical direction

9. A lithographic apparatus comprising the linear motor motion system according to any one of the preceding clauses.

10. The lithographic apparatus according to clause 9, wherein the object is one of a substrate stage and a mask stage of the lithographic apparatus.

11. A method of driving a linear motor motion system, the linear motor motion system comprising: a magnetic track; a coil unit, including a plurality of coils wound about respective ferromagnetic cores, a bearing configured to guide the coil unit along the magnetic track, wherein the bearing is constructed and arranged to only allow substantial movement of the coil unit relative to the magnetic track in a first direction; the method comprising providing input signals to each of the coils, wherein the input signals are provided to generate an actuation force in the first direction to move the object in the first direction and a compensation force in a second direction perpendicular to the first direction to at least partly compensate a disturbance force in the second direction.

12. The method according to clause 11, comprising providing a disturbance force profile as a function of a position in the first direction.

13. The method according to clause 12, wherein the disturbance force profile comprises 4 sine functions dependent on the position in the first direction.

14. The method according to clause 12 or 13, comprising generating a disturbance force signal using the disturbance force profile and the position in the first direction.

15. The method according to clause 14, comprising determining an actuation force signal from a setpoint signal of the linear motor motion system, the actuation force signal representing a force by the linear motor in the first direction, scaling the disturbance force signal by the actuation force signal to determine a compensation force signal, and deriving the input signals as provided to each of the coils using the actuation force signal and the compensation force signal.

16. The method according to any one of clauses 11 - 15, comprising determining the position in the first direction from one of the setpoint signal of the linear motor motion system and a position measurement signal representing a measured position of the linear motor motion system.