• 专利附录
  • 专利说明
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    • 专利摘要:
    The invention provides an electromagnetic actuator comprising: - a first member and a second member configured to co-operate With the first member to, in use, generate a force in a first direction; - the first member comprising a permanent magnet assembly and a first magnetic member, the permanent magnet and the first magnetic member forming a first magnetic circuit having a first gap; - the second member comprising a coil member configured to, in use, be arranged at least partly inside the first gap, and, When energized, generated an electromagnetic force in the first direction; - the second member further comprising a second magnetic member, the permanent magnet assembly, the first magnetic member and the second magnetic member forming a second magnetic circuit having a second gap, the second magnetic circuit being configured to, in use, generate a reluctance force in the first direction.
    公开号:NL2023571A
    申请号:NL2023571
    申请日:2019-07-25
    公开日:2020-06-05
    发明作者:Martinus Josephus Fischer Olof；Butler Hans；Marinus Maria Rovers Johannes；Hartger Kimman Maarten；Yang Tao
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    ELECTROMAGNETIC ACTUATOR, POSITION CONTROL SYSTEM AND LITHOGRAPHIC APPARATUS
    FIELD
    [0001] The present invention relates to the field of electromagnetic actuators which can e.g. be applied for positioning objects in a lithographic apparatus.
    BACKGROUND
    [0002] 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).
    [0003] 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.
    [0004] In a lithographic apparatus various object or components require an accurate positioning or displacement during the operation of the apparatus. Such objects or components may e.g. be object tables supporting an object such as a patterning device or a substrate, optical components such as mirrors or lenses. In order to position or displace such objects or components, solutions have been proposed which apply passive magnetic arrangements which generate a bias force to compensate for the weight of the object or component, and electromagnetic actuators for generating a control force for controlling a position or displacement of the object or component. Such solutions enable the generation of the required bias force substantially without dissipation. Such solutions however may however occupy a comparatively large space, which may not always be available. Present solutions wherein the passive levitation is combined with an active actuation function, result in an active function with a limited efficiency due to the dual function.
    SUMMARY
    [0005] It is an object of the present invention to provide in an alternative manner to position or displace objects or components such as objects or components in a lithographic apparatus. According to an aspect of the invention, there is provided an electromagnetic actuator comprising:
    a first member and a second member configured to co-operate with the first member to, in use, generate a force in a first direction;
    the first member comprising a permanent magnet assembly, the first member forming a first magnetic circuit having a first gap;
    the second member comprising a coil member configured to, in use, be arranged at least partly inside the first gap, and, when energized, generated an electromagnetic force in the first direction; the second member further comprising a second magnetic member, the first member and the second magnetic member forming a second magnetic circuit having a second gap, the second magnetic circuit being configured to, in use, generate a reluctance force in the first direction.
    [0006] The electromagnetic actuator according to the present invention enables the positioning of an object or component in an efficient and compact manner. The electromagnetic actuator according to present invention provides an integrated design in which both an electromagnetic force and a reluctance force are generated, both forces acting in substantially the same direction. Such an approach enables an efficient operation, in particular in case the actuator is to provide a substantially constant force, e.g. to compensate for the weight of the object or component.
    [0007] According to another aspect of the present invention, there is provided a position control system comprising:
    an electromagnetic actuator according to the invention, and a control unit configured to determine a control signal for controlling a current applied to the coil member of the electromagnetic actuator..
    [0008] According to yet another aspect of the present invention, there is provided a lithographic apparatus comprising an electromagnetic actuator according to the invention and/or a position control system according to the invention.
    BRIEF DESCRIPTION OF THE DRAWINGS
    [0009] 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 depicts a first embodiment of an electromagnetic actuator according to the present invention;
    Figures 5 a and 5b schematically depict a generated reluctance force and associated stiffness of an actuator according to the present invention.
    Figure 6 schematically illustrates a position control system according to the present invention;
    Figure 7 depicts a second embodiment of an electromagnetic actuator according to the present invention.
    Figure 8 depicts a second embodiment of an electromagnetic actuator according to the present invention
    DETAILED DESCRIPTION
    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).
    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.
    [00010] 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.
    [00011] 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.
    [00012] 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.
    [00013] In an embodiment, the projection system PS and/or the illumination system IL comprises one or more electromagnetic actuators according to the present invention for positioning a component of said system. Such components may e.g. be mirrors or lenses or masking arrangements such as reticle masking blades.
    [00014] 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.
    [00015] 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.
    [00016] 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 beamB. 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.
    [00017] 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.
    [00018] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axis, i.e., an x-axis, a y-axis and a z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y-axis is referred to as an Ry-rotation. A rotation around about the z-axis is referred to as an Rz-rotation. The xaxis 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,
    [00019] 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 BE, a balance mass BM, a metrology frame ME 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.
    [00020] 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.
    [00021] 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.
    [00022] 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.
    [00023] 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,+Ist order, -1st order, +2nd order and -2nd 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.
    [00024] 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.
    [00025] 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 longstroke 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.
    [00026] The first positioner PM and the second positioner PW each are provided with an actuator to move respectively the mask support MT and the substrate support WT. The actuator may be a linear actuator to provide a driving force along a single axis, for example the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axis. The actuator may be a planar actuator to provide a driving force along multiple axis. For example, the planar actuator may be arranged to move the substrate support WT in 6 degrees of freedom. The actuator may be an electro-magnetic actuator comprising at least one coil and al 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 such as an electromagnetic actuator according to the present invention.
    [00027] 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.
    [00028] The present invention relates to an electromagnetic actuator as can be applied in a lithographic apparatus as discussed above, e.g. for the positioning or displacement of an object or component of the apparatus.
    [00029] Figure 4 schematically shows a first embodiment of an actuator 100 according to the present invention. In the embodiment as shown, the electromagnetic actuator 100 comprises a first member 110 and a second member 120, the second member 120 being configured to co-operate with the first member 110 to, in use, generate a force in a first direction, the first direction being indicated by the arrow 130. The embodiment as shown describes an axisymmetric actuator, the actuator being symmetrical about the indicated axis 140, the axis 140 extending in the first direction as indicated by the arrow 130. In the embodiment as shown, the first member 110 comprises a permanent magnet or permanent magnet assembly 150 and a first magnetic member 160, 170. Within the meaning of the present invention, a magnetic member or element refers to a magnetically conductive part or member or element, i.e. a feature or component made of or comprising a material having a relative permeability μΓ significantly higher than 1. Examples of such materials include ferromagnetic materials such as iron or alloys such as CoFe. In the embodiment as shown, the permanent magnet 150 comprises a radially magnetized ring shaped permanent magnet 150, the magnetisation direction being indicated by the arrow 150.1. In an embodiment, such a permanent magnet 150 may also comprise a plurality of segments, rather than consisting of a single permanent magnet. In the embodiment as shown, the first magnetic member comprising two magnetic members 160, 170. In the embodiment as shown, the magnetic members 160, 170 are two concentrically arranged hollow cylinders. Cylinder 160 having an inner radius 160.1 and an outer radius 160.2, cylinder 170 having an inner radius 170.1 and an outer radius 170.2. In the embodiment as shown, the permanent magnet 150 and the first magnetic member 160, 170 forming a first magnetic circuit. A magnetic flux path of the first magnetic circuit is indicated by the dotted line 180. In the embodiment as shown, the first magnetic circuit has a first gap 190. In the embodiment as shown, the first gap 190 extends in the radial direction and is defined by the outer surface 160.3 of the cylinder 160 and the inner surface 170.3 of the cylinder 170. In the embodiment as shown, the gap 190 thus has a size equal to the difference between the inner radius 170.1 of the cylinder 170 and the outer radius 160.2 of the cylinder 160. In the embodiment as shown, the magnetic flux as generated by the permanent magnet 150 and guided by the first magnetic member 160,170 crosses the first gap 190 in a direction substantially perpendicular to the first direction as indicated by the arrow 130, i.e. the magnetic flux that crosses the first gap 190 propagates radially inwards from the inner surface 170.3 of the cylinder 170 to the outer surface 160.3 of the cylinder 160.
    [00030] In the embodiment as shown, the second member 120 comprises a coil member 200 configured to, in use, be arranged at least partly inside the first gap 190, and, when energized, generates an electromagnetic force in the first direction 130, In the present invention, an electromagnetic force is generally indicated as Fe.
    [00031] The co-operation of the coil member 200 and the first member 110 of the electromagnetic actuator 100 as shown may be considered similar to the operation of a voice coil motor. When an electric current is supplied to the coil member 200, the interaction of the current carrying conductors of the coil member 200 with the magnetic field crossing the gap 190 will result in the generation of an electromagnetic force Fe in the first direction 130. In case the magnetic field as perceived by the coil member 200 is substantially homogeneous, the force as generated by the interaction of the current carrying coil member 200 and the first member 110 will be substantially independent of the relative position of the coil member 200 and the first member 110 in the first direction 130. Such a property of the generated electromagnetic force may be qualified or characterised by the stiffness of the generated force. Such a stiffness C may be expressed as:
    wherein
    AF = the variation of the generated electromagnetic force Fe
    Az = the corresponding relative displacement of the coil member 200 and the first member in the direction of the generated force, e.g. the Z-direction or the indicated direction 130.
    [00032] Typically, it may be advantageous to apply an actuator having a comparatively small stiffness C, because this enables to mitigate the transmission of vibrations towards the supported or suspended object or component. In general, electromagnetic actuators such as Lorentz actuators may be designed in such manner that they have a comparatively low stiffness. Typically, a Lorentz actuator or voice coil actuator may be designed to have a stiffness C < 5e2 N/m over its operating range, e.g. a range of 1-2 mm or less. The stiffness C may e.g. be < 2-3e2 N/m. It can however be pointed out that, depending on the application, in particular the required force, the stiffness C may be higher.
    [00033] It can further be pointed out that the electromagnetic actuator 100 according to the present invention may be designed to have a particular stiffness or stiffness range. In case the coil member 200 experiences, over its operating range, i.e. when being displaced along the first direction relative to the first member 110, a substantially constant magnetic flux, the stiffness C will be low. However, the first magnetic circuit may be designed such that, when the coil member 200 is displaced along the first direction, the magnetic flux as experienced by the coil member 200 varies. This can e.g. be realized by providing at least one of the cylinders 160, 170 with a tapered portion, i.e. a portion whereby the diameter, e.g. the inner radius 170.1 of the cylinder 170 or the outer radius 160.2 of the cylinder 160 varies along the first direction. By doing so, the size of the gap 190 varies along the first direction as indicated by the arrow 130 and, as a result, the flux density of the magnetic flux that crosses the gap 190 will vary as well along the first direction 130. As such, the generated electromagnetic force Fe, for a given current applied to the coil member 200, will vary as well along the first direction 130. By doing so, the interaction of the coil member 200 and the first magnetic circuit may thus be designed to have a particular stiffness C or stiffness range.
    [00034] In accordance with the present invention, the second member 120 further comprises a second magnetic member 210. The second magnetic member 210 is configured to form a second magnetic circuit with the permanent magnet 150 and the first magnetic member 160, 170. The dotted line 220 schematically indicates a magnetic flux path of the second magnetic circuit. In the embodiment as shown, the second magnetic circuit as formed by the second magnetic member 210 and the first member 110 has a second gap 230.
    [00035] In the embodiment as shown, the second gap 230 extends in the first direction 130 and is defined by a surface 210.1 of the second magnetic member 210 and a surface of the first member 110, in particular the surfaces 160.4 and 170.4 of the first magnetic member 160, 170. The second magnetic circuit as shown is configured to, in use, generate a reluctance force in the first direction 130. As will be appreciated by the skilled person, due to the magnetic flux as generated in the second magnetic circuit, i.e. a magnetic flux propagating along the dotted line 220, a reluctance force will be generated between the second magnetic member 210 and the first member 110, in particular the first magnetic member 160, 170 of the first member 110. In the present invention, a reluctance force is generally indicated as Fr. [00036] The reluctance force FR as generated will be directed so as to diminish the second gap 230. Phrased differently, the magnetic flux in the second magnetic circuit 220 causes an attractive force between the second magnetic member 210 and the first magnetic member 160, 170.
    [00037] It can be noted that such a reluctance force Fr depends on the position of the first member relative to the second member in the first direction. In particular, as will be acknowledged by the skilled person, the generated reluctance force Fr will increase when the size of the second gap 230 decreases. The variation of the reluctance force Fr in dependency of the variation of the gap 230 can be expressed as a stiffness, as e.g. discussed above.
    [00038] The stiffness characterizing the generated reluctance force Fr may e.g. depend on the actual size of the gap 230 and e.g. on the thickness of the applied second magnetic member 210. This is illustrated in Figures 5a and 5b.
    [00039] Figure 5a schematically shows a generated reluctance force Fr as a function of the size of the gap 230, for three different sized second magnetic members 210. hi the embodiment as shown, the gap size is varied from 2 mm to 6 mm. In Figure 5a, three graphs are shown, hi graph (a), the second magnetic member 210 has a thickness in the Z-direction of 2 mm, in graph (b), the second magnetic member 210 has a thickness in the Z-direction of 0.5 mm, in graph (c), the second magnetic member 210 has a thickness in the Z-direction of 0.3 mm.
    [00040] Figure 5b schematically shows the corresponding stiffness Cz for the graphs (a), (b) and (c) of Figure 5a, as a function of the gap 230, i.e. the gap between the first magnetic member 160, 170 and the second magnetic member 210. In case the actuator is operating with a nominal gap 230 in the range of 5-6 mm, the stiffness characterizing the generated reluctance force would e.g. be -5e3 N/m.
    [00041] In general, as will be appreciated by the skilled person, the application of a reluctance force to compensate for a substantially constant counteracting force such as a gravitational force, may result in an unstable operation, when no measures are taken. In the present invention, the application of an actuator which both generates an electromagnetic force Fe and a reluctance force Fr enables a stable operation while at the same time reducing the dissipation of the actuator, compared to the application of a conventional electromagnetic actuator such as a Lorentz actuator or a voice coil actuator.
    [00042] The electromagnetic actuator 100 according to the present invention generates, during use, both an electromagnetic force due to interaction between the first member 110 and the coil member 200 of the second member 120 and a reluctance force Fr due to interaction between the first member 110 and the second magnetic member of the second member 220. In accordance with the present invention, both forces act in substantially the same direction, i.e. the first direction 130.
    [00043] In an embodiment, the electromagnetic actuator 100 according to the present invention may advantageously be applied for the positioning of components or elements, in particular for the positioning of such components or elements in the vertical direction, also referred to as the Z-direction. In such embodiments, the purpose of the electromagnetic actuator or actuators as applied is both the positioning of the component or element as the compensation of the gravitational force acting on the component or elements. Examples of such components or elements may e.g. be an object table as applied in a lithographic apparatus or an optical component as applied in a projection system PS of such an apparatus an immersion hood as applied in a lithographic apparatus or a cooling hood as applied in an EUV lithographic apparatus. In such embodiment, the one or more actuators as applied need to continuously generate a sufficient force to compensate for the weight of the component or element as well as a control force for controlling a position of the component or element.
    [00044] In case of such an arrangement, the electromagnetic actuator 100 according to the present invention may advantageously be applied because the generation of the reluctance force Fr does not require the application of a current in the coil member 200. The reluctance force Fr can thus be generated substantially without causing any dissipation in the actuator. By appropriate dimensioning of the electromagnetic actuator 100, one can e.g. ensure that part of the required force for compensating the weight of the suspended object is provided by the reluctance force Fr. In an embodiment, the electromagnetic actuator 100 according to the present invention may be designed in such manner that approximately 50% of the weight is compensated by the generated reluctance force Fr, when the object is in a nominal position. In such an arrangement, the electromagnetic force Fe as generated by interaction of current carrying coil member 200 and the first member 110 only needs to compensate 50% of the weight to suspend the object.
    [00045] In an embodiment, the electromagnetic actuator 100 according to the present invention may be designed in such manner that > 50% of the weight is compensated by the generated reluctance force Fr, when the object is in a nominal position, e.g. 80 - 90% of the weight.
    [00046] However, as can be derived from the above, the electromagnetic actuator 100 according to the present invention will behave as an actuator having a negative stiffness in the force generating direction, e.g. the Z-direction. When such an actuator is thus applied to suspend an object or component, an unstable situation would occur. In order to provide in a stable position control of the object that is suspended, a sufficiently fast response of the generated electromagnetic force Fe as generated may be required.
    [00047] This is schematically illustrated in the following Figures.
    [00048] Figure 6 schematically illustrates a position control system according to the present invention, whereby the position control system is applied for the positioning of an object 600 having a mass m relative to a frame 610. In the embodiment as shown, the position control system comprises an electromagnetic actuator according to the present invention, represented by the forces Fe and Fr , and a control unit or controller 640. In the embodiment as shown, the object 600 is deemed to be suspended relative to the frame 610 by means of a force Ft generated by an electromagnetic actuator 100 according to the present invention. The force Ft as generated can be considered, as described above, a combination of a reluctance force Fr and an electromagnetic force Fe; Ft= Fe + Fr. The electromagnetic force Fe , indicated by the arrow 630, can be considered to be substantially proportional to the current as supplied to the coil member of the actuator, e.g. coil member 200 as shown in Figure 4. Further, the reluctance force Fr as generated may be represented by a spring 620 acting on the object 600 and attempting to pull the object 600 upwards. As discussed above, the reluctance force Fr is characterized by having a negative stiffness, the spring 620 representing the reluctance force Fr can thus be characterized by a negative spring-constant equal to the stiffness Cz as e.g. shown in Figure 5b. As a result of the negative stiffness or spring-constant, the position of the object 600 in the Z-direction can be described as an unstable equilibrium.
    [00049] The suspension of the object 600 as schematically shown in Figure 6 can thus be represented by a mass-spring system with a negative spring-constant, i.e. an unstable system. In order to provide in a stable positioning of the object 600, a control of the generated force Ft, needs to be implemented. In order to realize such a control, the position control system according to the present invention further comprises a control unit or controller 640 as illustrated in Figure 6. Such a control unit or controller 640 may e.g. be embodied as a microprocessor or microcontroller or computer or the like. Such a control unit 640 may e.g. have an input terminal 640.1 for receiving input signals. Such input signals may e.g. include a desired position of the object 600. In the embodiment as shown, signal 640.2 represents such a desired position or position set point. In the embodiment as shown, the control unit 640 further receives, at the input terminal 640.1 a position measurement signal MS representing the position of the object 600 relative to the frame 610 in the Z-direction. It can be pointed out that the position measurement signal MS as applied by the control unit or controller 640 to provide in a stable operation may also represent the position of the object 600 relative to another object, different from the frame 610 to which the object 600 is mounted. Such an object may e.g. be an optical element such as a mirror or a lens of a projection system of a lithographic apparatus.
    [00050] Based on the difference between the position set point 640.2 and the actual position represented by the position measurement signal MS, the control unit or controller 640 may then generate a control signal CS for controlling the actuator according to the present invention. In order to do so, the control unit or controller 640 may comprise a PID controller or the like.
    [00051] With respect to the required or desired bandwidth of the controller the following can be mentioned. As a design rule to control a mechanical system having a negative stiffness, the controller bandwidth should be above the cut-off frequency fo:
    f0 = * /-k/m
    Ζπ wherein:
    k = the negative stiffness, and m = the mass of the object.
    [00052] For a mass m - 1 kg and a stiffness k - -3e3 N/m, the cut-off frequency amounts to approximately 10 Hz. hi order to realize a stable position control, the controller bandwidth should thus at least be 10 Hz. Preferable, in order to create a phase advantage with the derivative action of the controller, the bandwidth should preferable be higher than the cut-off frequency fo, preferably at least three times higher. As such, in the embodiment as illustrated in Figure 6, the control unit 640 may have a bandwidth of three times the cut-off frequency fo of the mass-spring system.
    [00053] The control signal CS as generated by the control unit 640 may be outputted via an output terminal 640.3 of the control unit 640 and applied to control the electromagnetic force Fe as generated by the electromagnetic actuator according to the present invention, e.g. by controlling the current as supplied to the coil member of the actuator.
    [00054] The electromagnetic actuator 100 according to the present invention as schematically shown in Figure 4 has an axisymmetric design. The present invention is however not limited to such a design. The electromagnetic actuator 100 according to the present invention may also be designed using substantially planar components, rather than circular or cylindrical components.
    [00055] Figure 7 schematically shows such an embodiment. Figure 7 schematically shows a crosssectional view of an electromagnetic actuator 300 according to another embodiment of the present invention, in the XZ-plane. In the embodiment as shown, the electromagnetic actuator 300 comprises a first member 310 and a second member 320, the second member 320 being configured to co-operate with the first member 310 to, in use, generate a force in a first direction, the first direction being indicated by the arrow 330. In the embodiment as shown, the first member 310 comprises a permanent magnet assembly 350 and a first magnetic member 360, 370 configured to guide, at least partly, the magnetic flux as generated by the permanent magnet assembly 350. In the embodiment as shown, the permanent magnet assembly 350 comprises 4 permanent magnets 350.1, 350.2, having a magnetisation direction as indicated by the arrows inside the magnets. In particular, the permanent magnet assembly 350 comprises a first pair of facing permanent magnets 350.1 and a second pair of facing permanent magnets 350.2. In the embodiment as shown, the first magnetic member 360, 370 comprises two magnetic members 360, 370. In the embodiment as shown, the magnetic members 360, 370 may e.g. be two magnetic yokes, configured to guide the magnetic flux as generated by the permanent magnets 350.1, 350.2. In the embodiment as shown, the permanent magnets 350 and the first magnetic member 360, 370 form a first magnetic circuit. A magnetic flux path of the first magnetic circuit is indicated by the dotted line 380. As can be seen, the first magnetic circuit has a first gap 390. in the embodiment as shown, the first gap 390 extends in the indicated X-direction and is defined by the distance between two facing magnets of the permanent magnet assembly 350 in the X-direction, i.e. the two facing magnets 350.1 and/or the two facing magnets 350.2. In the embodiment as shown, the magnetic flux as generated by the permanent magnet assembly 350 and guided by the first magnetic member 360, 370 crosses the first gap 390 in a direction substantially perpendicular to the first direction 330.
    [00056] In the embodiment as shown, the second member 320 comprises a coil member 400 configured to, in use, be arranged at least partly inside the first gap 390, and, when energized, generated an electromagnetic force Fe in the first direction 330.
    [00057] The co-operation of the coil member 400 and the first member 310 may be considered similar to the operation of a Lorentz actuator. When an electric current is supplied to the coil member 400, the interaction of the current carrying conductors of the coil member 400 with the magnetic field crossing the gap 390 will result in the generation of a force in the first direction 330. In case the magnetic field as perceived by the coil member 400 is substantially homogeneous, the force as generated by the interaction of the current carrying coil member 400 and the first member 310 will be substantially independent of the relative position of the coil member 400 and the first member 310 in the first direction 330, i.e. the generated electromagnetic force may be characterised by a comparatively low stiffness in the Z-direction. [00058] In accordance with the present invention, the second member 320 further comprising a second magnetic member 410, the second magnetic member 410 being configured to form a second magnetic circuit, a magnetic flux path of the second magnetic circuit being indicated by the dotted line
    420. As can be seen, the second magnetic circuit is formed by the second magnetic member 410, the permanent magnet assembly 350, in particular the second pair of facing permanent magnets 350.2 and the first magnetic member 360, 370. In the embodiment as shown, the second magnetic circuit as formed by the second magnetic member 410 and the first member 310 has a second gap 430. In the embodiment as shown, the second gap 430 extends in the first direction 330 and is defined by a surface 410.1 of the second magnetic member 410 and a surface of the first member, in particular the surfaces 360.4 and 370.4 of the first magnetic member 360, 370.
    [00059] The second magnetic circuit as shown is configured to, in use, generate a reluctance force in the first direction 330. As will be appreciated by the skilled person, due to the magnetic flux as generated in the second magnetic circuit, i.e. a magnetic flux propagating along the dotted line 420, a reluctance force Fr will be generated between the second magnetic member 410 and the first member 310, in particular the first magnetic member 360, 370 of the first member 310, the magnetic force being directed so as to diminish the second gap 430. Phrased differently, the magnetic flux in the second magnetic circuit 420 causes an attractive force between the second magnetic member 410 and the first magnetic member 360, 370.
    [00060] In view of the above, it can be noted that the electromagnetic actuator 300 as schematically shown in Figure 7 may be operated in substantially the same manner as the actuator schematically shown in Figure 4.
    [00061] With respect to the permanent magnet assemblies as applied in the electromagnetic actuators according to the present invention, it can be pointed out that more advanced permanent magnet arrangements such as Halbach arrangements may be applied as well, thereby further increasing the force density and/or efficiency of the electromagnetic motor.
    [00062] With respect to permanent magnet assembly 350 of the actuator 300 shown in Figure 7, it can be pointed out that the first pair of facing permanent magnets 350.1 need not be identical to the second pair of facing permanent magnets 350.2. hi particular, the second pair of facing permanent magnets 350.2, which, as can be seen, contributes to the formation of the second magnetic circuit 420, may be designed to be stronger or larger than the first pair of facing permanent magnets 350.1. By an appropriate selection or design of both pairs of permanent magnets 350.1, 350.2, together with an appropriate design of the gaps 390 and 430, a desired magnetic flux distribution between the first magnetic flux path 380 and the second magnetic flux path 420 may be realised.
    [00063] In an alternative embodiment for the one as shown in Figure 7, the radial position of the permanent magnets 350.1, 350.2 and the coil member 400 is exchanged, meaning that the distance between the permanent magnets becomes smaller than the diameter of coil member 400 (i.e. the permanent magnets are located inside the coil member). In the alternative embodiment the magnetization direction of the permanent magnets forming 350.1 and 350.2 are magnetized in an opposite direction which is different in comparison with the embodiment as shown in Figure 7 wherein the magnetization direction of the permanents magnets forming 350.1 and 350.2 are in a similar direction (+x and -x) respectively. In this alternative embodiment the first magnetic member 360, 370 functions as back iron. It is well-known by the skilled person that by using back iron the steepness of a motor [NA2/W] increases. In a preferred embodiment the rectangular shape of the magnetic member 360, 370 is changed into Lshaped back iron by decreasing the internal diameter of the top part of the first magnetic members 370, 371. Such a L-shape is advantageous as in addition to its primary function of increasing the motor steepness, the top disc part of magnetic members 360, 370 also creates an attractive reluctance force to the permanent magnets 350.1, 350.2. This partly compensates for the gravity force of the moving permanents magnets over a large stroke along the Z-direction resulting in less nonlinearity due to the reluctance force.
    [00064] In the embodiments as shown in Figures 4 and 7, the first members 110, 310 of the electromagnetic actuators 100, 300 according to the present invention comprise a first magnetic member 160,170 resp. 360, 370. It can be pointed out that the present invention may also be embodied as having a first member comprising a permanent magnet or permanent magnet assembly.
    [00065] Such an embodiment is schematically shown in Figure 8. Figure 8 schematically shows an electromagnetic actuator 800 according to the present invention. The embodiment as shown is an axisymmetric design about an axis 805. Other non-axisymmetric designs can however be considered as well. In the embodiment as shown, the electromagnetic actuator 800 comprises a first member 810 and a second member 820 configured to co-operate with the first member 810 to, in use, generate a force in a first direction 830. In the embodiment as shown, the first member 810 comprises a permanent magnet assembly, in particular a radially magnetized permanent magnet ring 810. In the embodiment as shown, the first member 810 forming a first magnetic circuit, e.g. indicated by the magnetic flux lines 840. The first magnetic circuit may be considered to have a first gap 850, extending in a direction perpendicular to the first direction 830. In the embodiment as shown, the second member 820 comprising a coil member 860 configured to, in use, be arranged at least partly inside the first gap 850, and, when energized, generated an electromagnetic force in the first direction 830. In the embodiment as shown, the coil member 860 comprises a ring shaped coil, the second member 820 further comprising a second magnetic member 870, the first member 810 and the second magnetic member 870 forming a second magnetic circuit, e.g. indicated by the magnetic flux line 880. The second magnetic circuit can be considered to have a second gap 890, the second gap 890 extending in the first direction 830. In accordance with the present invention, the second magnetic circuit is configured to, in use, generate a reluctance force in the first direction 830. As such, the electromagnetic actuator 800 enables the generation of both an electromagnetic force Fe and a reluctance force Fr, substantially in the same manner as discussed above with reference to Figures 4 and 7.
    [00066] 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, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.
    [00067] 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.
    [00068] 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.
    [00069] 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.
    [00070] 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 claim set out below. Other aspects of the invention are set-out as in the following numbered clauses.
    1. An electromagnetic actuator comprising:
    a first member and a second member configured to co-operate with the first member to, in use, generate a force in a first direction;
    the first member comprising a permanent magnet assembly, the first member forming a first magnetic circuit having a first gap;
    the second member comprising a coil member configured to, in use, be arranged at least partly inside the first gap, and, when energized, generated an electromagnetic force in the first direction; the second member further comprising a second magnetic member, the first member and the second magnetic member forming a second magnetic circuit having a second gap, the second magnetic circuit being configured to, in use, generate a reluctance force in the first direction.
    2. The electromagnetic actuator according to clause 1, wherein the first gap extends in a second direction substantially perpendicular to the first direction.
    3. The electromagnetic actuator according to any of the preceding clauses, wherein the second gap extends in the first direction.
    4. The electromagnetic actuator according to any of the preceding clauses, wherein the actuator is axisymmetric about an axis extending in the first direction.
    5. The electromagnetic actuator according clause 4, wherein the first member comprises a first magnetic member, wherein the first magnetic member comprises two concentric magnetic cylinders.
    6. The electromagnetic actuator according to clause 5, wherein the first gap is a radial gap extending between an outer surface of an inner cylinder of the two concentric magnetic cylinders and an inner surface of an outer cylinder of the two concentric magnetic cylinders.
    7. The electromagnetic actuator according to clause 5 or 6, wherein the second gap extends between an end surface of the two concentric magnetic cylinders and a surface of the second magnetic member.
    8. The electromagnetic actuator according to any of the clauses 5 to 7, wherein the coil member comprises a substantially cylindrical coil arranged, in use, at least partially in between the two concentric magnetic cylinders.
    9. The electromagnetic actuator according to any of the clauses 5 to 8, wherein at least one of the concentric magnetic cylinders has a tapered portion.
    10. The electromagnetic actuator according to any of the clauses 5 to 9, wherein at least one of the concentric magnetic cylinders is L-shaped.
    11. The electromagnetic actuator according to any of the preceding clauses, wherein the coil member is mounted to the second magnetic member.
    12. The electromagnetic actuator according to clause 1, wherein the permanent magnet arrangement comprises a first pair of facing permanent magnets and a second pair of facing permanent magnets.
    13. The electromagnetic actuator according to clause 12, wherein the first gap is a gap extending between two facing surfaces of the first pair and/or the second pair of facing permanent magnets.
    14. The electromagnetic actuator according to clause 12 or 13, wherein the first member comprises a first magnetic member and wherein the first magnetic circuit is substantially formed by the first magnetic member, the first pair of facing permanent magnets and the second pair of facing permanent magnets.
    15. The electromagnetic actuator according to clause 14, wherein the second magnetic circuit is substantially formed by the first magnetic member, the second pair of facing permanent magnets and the second magnetic member.
    16. The electromagnetic actuator according to clause 1, wherein the first member further comprises a first magnetic member, and wherein the permanent magnet and the first magnetic member form the first magnetic circuit having the first gap.
    17. The electromagnetic actuator according to clause 16, wherein the permanent magnet assembly, the first magnetic member and the second magnetic member form the second magnetic circuit having the second gap.
    18. A position control system comprising:
    an electromagnetic actuator according to any of the preceding clauses, and a control unit configured to determine a control signal for controlling a current applied to the coil member of the electromagnetic actuator.
    19. The position control system according to clause 18, further comprising a position measurement system configured to generate a position measurement signal representing a position of the first member relative to the second member in the first direction.
    20. The position control system according to clause 19, wherein the control unit comprises an input terminal configured to receive the position measurement signal and an output terminal configured to output the control signal.
    21. The position control system according to clause 20, wherein the control unit is further configured to receive a position set point via the input terminal and wherein the control unit is configured to determine the control signal based on the position measurement signal and the position set point.
    22. A lithographic apparatus comprising an electromagnetic actuator according to any of the clauses 1 to 17 and/or a position control system according to any of the clauses 18 to 21.
    权利要求:
    Claims (1)
    [1]
    1. A device arranged for exposing a substrate.
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    引用文献:
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    US6020964A|1997-12-02|2000-02-01|Asm Lithography B.V.|Interferometer system and lithograph apparatus including an interferometer system|
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    US7183674B2|2003-11-06|2007-02-27|Carl Zeiss Smt Ag|Hermetically sealed elements of an actuator|
    DE102005043569A1|2005-09-12|2007-03-22|Dr. Johannes Heidenhain Gmbh|Position measuring device|
    EP1953903A1|2007-01-30|2008-08-06|Magtronics Technology Inc.|Voice coil motor and method of using a magnetic restoring force for displacement control|CN112688531A|2020-12-18|2021-04-20|上海大学|Voice coil motor active suspension|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    EP18191057|2018-08-28|
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