Superconducting magnet assembly, planar motor, and lithography apparatus

Abstract

The present invention provides a superconducting (SC) magnet assembly for a planar motor, the superconducting magnet assembly comprising: a two-dimensional (2D) array of SC coils configured to generate a two-dimensional spatially alternating magnetic field; and a shield disposed on a side of the 2D array of SC coils that faces a mover of the planar motor during use, the shield being configured to mitigate magnetic field changes experienced by the 2D array of SC coils, the shield comprising a layer of conductive material, the layer extending over an area substantially covering the 2D array of SC coils, the layer of conductive material having a thickness variation across the area, the thickness variation across the area being related to geometric parameters of the 2D array of SC coils.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Application No. 22191098.7, filed August 18, 2022, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a superconducting magnet assembly for a planar motor, to a planar motor and to a lithographic apparatus comprising such a planar motor. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (often referred to as a "design layout" or "design") in a patterning device (e.g., mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually decreased, while the amount of functional elements, such as transistors, per device has steadily increased for decades, following a trend commonly referred to as "Moore's Law." To accommodate Moore's Law, the semiconductor industry pursues technologies that enable the creation of smaller and smaller features. To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. To form smaller features on a substrate than lithography apparatuses using radiation having a wavelength of, for example, 193 nm, lithography apparatuses using extreme ultraviolet (EUV) radiation, having wavelengths in the range of 4 nm to 20 nm, e.g., 6.7 nm or 13.5 nm, may be used.

[0005]

[0005] In general, there is an aim to increase the productivity and accuracy of apparatuses such as lithography apparatuses. To increase the productivity of lithography apparatuses, more powerful motors may be applied to position the substrate and the patterning device. An example of such a motor is a superconducting planar motor. A superconducting motor applies superconducting coils to generate a magnetic field. The achievable magnetic field strength is typically much higher than that of conventional planar motors that apply, for example, permanent magnets. In order to generate the magnetic field, it is important that the applied superconducting coils maintain a superconducting state during operation. It has been observed that in known configurations, there may be a risk that the coils lose their superconducting state due to losses induced in the coils. Summary of the Invention

[0006]

[0006] An object of the present invention is to provide a superconducting magnet assembly for a planar motor in which the superconducting state of the coils of the assembly is more easily maintained.

[0007] According to one aspect of the present invention, there is provided a superconducting (SC) magnet assembly for a planar motor, the superconducting magnet assembly comprising: a two-dimensional (2D) array of SC coils configured to generate a two-dimensional spatially alternating magnetic field; a shield disposed on a side of the 2D array of SC coils that faces a mover of the planar motor during use, the shield being configured to mitigate magnetic field changes experienced by the 2D array of SC coils; It is equipped with The shield comprises a layer of conductive material extending over an area substantially covering the 2D array of SC coils, the layer of conductive material having a thickness variation across the area, the thickness variation across the area being related to a geometric parameter of the 2D array of SC coils.

[0008]

[0008] According to another aspect of the present invention, there is provided a planar motor for use in a lithographic apparatus, the planar motor comprising a superconducting magnet assembly according to the present invention.

[0009] According to another aspect of the present invention, there is provided a lithographic apparatus comprising a planar motor according to the present invention for displacing a substrate. [Brief explanation of the drawings]

[0010]

[0010] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0011] [Figure 1] 1 shows a schematic overview of a lithographic apparatus according to the present invention; [Figure 2] 2 illustrates a detailed view of a portion of the lithographic apparatus of FIG. 1; [Figure 3] 1 illustrates a schematic diagram of a position control system. [Figure 4] FIG. 1 illustrates a top view of a planar motor having a magnet assembly with permanent magnets. [Figure 5] 1 illustrates a top view of a 2D array of SC coils. [Figure 6] FIG. 1 illustrates a top view of a planar motor having a magnet assembly with a 2D array of SC coils. [Figure 7] FIG. 7 illustrates a side view of the planar motor of FIG. 6. [Figure 8] 1 illustrates a side view of a planar motor according to the present invention; [Figure 9] 1 illustrates a first example of a layer of conductive material that can be applied as a shield in the present invention. [Figure 10a] 10 illustrates further examples of layers of conductive material that can be applied as shields in the present invention. [Figure 10b] 10 illustrates further examples of layers of conductive material that can be applied as shields in the present invention. [Figure 10c]10 illustrates further examples of layers of conductive material that can be applied as shields in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0011] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 to 100 nm).

[0013] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" may also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0014] 1 schematically illustrates a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also called an 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 coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer table) WT configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW constructed to accurately position the substrate according to 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 the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. In an embodiment, the second positioner PW may include, for example, a planar motor according to the present invention.

[0015]

[0013] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the 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 the radiation. The illuminator IL may be used to condition the radiation beam B, so that it has a desired spatial and angular intensity distribution across its cross-section in the plane of the patterning device MA.

[0016]

[0014] The term "projection system" PS as used herein should be interpreted broadly as encompassing various types of projection systems, including refractive optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate depending on the exposure radiation used and / or other factors such as the use of an immersion liquid or the use of a vacuum. Where the term "projection lens" is used herein, this may be considered as synonymous with the more general term "projection system" PS.

[0017] The lithographic apparatus LA may be of a type in which at least a portion of the substrate W is covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system PS and the substrate W. This is also known as immersion lithography. Further information about immersion techniques is given in US Pat. No. 6,952,253, which is incorporated herein by reference.

[0018] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or a substrate W may be used to expose a pattern on a substrate W on one substrate support WT while a preparation step for a subsequent exposure of the substrate W is performed on a substrate W placed on another substrate support WT.

[0019] In addition to the substrate support WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor can be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage can hold multiple sensors. The cleaning device can be arranged to clean part of the lithographic apparatus, for example part of the projection system PS or part of the system for providing immersion liquid. When the substrate support WT is remote from the projection system PS, the measurement stage can be moved below the projection system PS.

[0020] In operation, the radiation beam B is incident on the patterning device MA, e.g., a mask, which is held on the mask support MT, and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. Using the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example, to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM, and possibly further position sensors (not explicitly shown in FIG. 1 ), can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks P1, P2 occupy dedicated target portions, it is possible to position them in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0021] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x, y, and z. Each of the three axes is orthogonal to the other two. Rotation about the x-axis is called Rx rotation. Rotation about the y-axis is called Ry rotation. Rotation about the z-axis is called Rz rotation. The x- and y-axes define a horizontal plane, while the z-axis is vertical. The Cartesian coordinate system is not a limitation of the invention and is used for clarity only. Alternatively, 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, so that the z-axis has a component along the horizontal plane.

[0022]

[0020] Figure 2 shows a more detailed view of part of the lithographic apparatus LA of Figure 1. The lithographic apparatus LA may comprise 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. The metrology frame MF may also support 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.

[0023]

[0021] 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 conservation of momentum, the driving force is also applied to the balance mass BM with the same magnitude but in a direction opposite to the desired direction. Typically, the mass of the balance mass BM is significantly greater than the mass of the second positioner PW and the moving parts of the substrate support WT.

[0024] In one embodiment, the second positioner PW is supported by the balance mass BM. For example, the second positioner PW then comprises a planar motor for levitating 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, the second positioner PW then comprises a linear motor, and the second positioner PW then comprises a bearing, such as a gas bearing, for levitating the substrate support WT above the base frame BF.

[0025] The position measurement system PMS may comprise any type of sensor suitable for determining the position of the substrate support WT. The position measurement system PMS may comprise any type of sensor suitable for determining the 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 interferometer and encoder system. The sensor may also 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.

[0026] The position measurement system PMS may comprise an encoder system. Encoder systems are known, for example, from US Patent Application No. 2007 / 0058173 A1, filed September 7, 2006, which is incorporated herein 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 and the secondary radiation beam may originate from the same radiation beam, i.e., an original radiation beam. At least one of the primary radiation beam and the secondary radiation beam is generated by diffracting the original radiation beam with a grating. If both the primary radiation beam and the secondary radiation beam are generated by diffracting the original radiation beam with a grating, the primary radiation beam must have a different diffraction order from the secondary radiation beams. The different diffraction orders are, for example, +1, −1, +2, and −2. 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 the phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal indicates the position of the encoder head relative to the grating. One of the encoder head or the grating may be located on the substrate structure WT. The other of the encoder head or the grating may be located on the metrology frame MF or the base frame BF. For example, multiple encoder heads are located on the metrology frame MF, while one grating is located on the top surface of the substrate support WT. In another example, one grating is located on the bottom surface of the substrate support WT, and one encoder head is located below the substrate support WT.

[0027] The position measurement system PMS may comprise an interferometer system. Interferometer systems are known, for example, from U.S. Pat. No. 6,020,964, filed July 13, 1998, which is incorporated herein by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror, and a sensor. The beam splitter splits the radiation beam 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 combine into a combined radiation beam. The combined radiation beam is incident on a sensor. The sensor determines the phase or frequency of the combined radiation beam. The sensor generates a signal based on the phase or frequency. The signal represents the displacement of the mirror. In one embodiment, the mirror is coupled to the substrate support WT. The reference mirror may be coupled to the metrology frame MF. In one embodiment, the measurement and reference beams are combined into a combined radiation beam by an additional optical component rather than a beam splitter.

[0028] 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 over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with relatively low accuracy relative to the projection system PS. The combination of the long-stroke module and the short-stroke module enables the first positioner PM to move the mask support MT over a large range of movement with high accuracy relative to the projection system PS. 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 over a small range of movement with high accuracy relative to the long-stroke module. The long-stroke module is arranged to move the short-stroke module over a large range of movement with relatively low accuracy relative to the projection system PS. Such a long-stroke module may, for example, comprise a planar motor according to the present invention. The combination of the long-stroke module and the short-stroke module enables the second positioner PW to move the substrate support WT relative to the projection system PS over a large range of movement with high accuracy.

[0029] The first positioner PM and the second positioner PW each include an actuator for moving the mask support MT and the substrate support WT, respectively. The actuator may be a linear actuator for providing a driving force along a single axis, for example, the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axes. The actuator may be a planar actuator for providing driving forces along multiple axes. For example, the planar actuator may be arranged to move the substrate support WT with six degrees of freedom. The actuator may be an electromagnetic actuator including 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 a current to the at least one coil. The actuator may be a moving magnet actuator, which has at least one magnet coupled to the substrate support WT or the mask support MT. The actuator may be a moving coil actuator, which has at least one coil coupled to the substrate support WT or the mask support MT. The actuator may be a voice coil actuator, a reluctance actuator, a Lorentz actuator, a piezoelectric actuator, or any other suitable actuator.

[0030] The lithographic apparatus LA includes a position control system PCS, as shown schematically in FIG. 3. The position control system PCS includes a setpoint generator SP, a feedforward controller FF, and a feedback controller FB. The position control system PCS provides drive signals to actuators ACT. The actuators ACT may be actuators of the first positioner PM or may be actuators of the second positioner PW. The actuators ACT drive a plant P, which may include a substrate support WT or a mask support MT. The output of the plant P is a position quantity, such as a position, velocity, or acceleration. The position quantity is measured by a position measurement system PMS. The position measurement system PMS generates a signal, which is a position signal representing the position quantity of the plant P. The setpoint generator SP generates a signal, which is a reference signal representing a desired position quantity of the plant P. For example, the reference signal represents a desired trajectory of the substrate support WT. The difference between the reference signal and the position signal forms the input of the feedback controller FB. Based on the input, the feedback controller FB provides at least a portion of the drive signal for the actuator ACT. The reference signal may form the input of a feedforward controller FF, based on which the feedforward controller FF provides at least a portion of the drive signal for the actuator ACT. The feedforward FF may utilize information about the mechanical properties of the plant P, such as mass, stiffness, resonant modes, and natural frequencies.

[0031] 4 shows a schematic top view of a known planar motor 200 that can be used in a lithographic apparatus for positioning a substrate support, such as the substrate support WT mentioned above. The planar motor 200 comprises a magnet assembly 210 comprising a number of permanent magnets 210.1 configured to generate a spatially alternating magnetic field in two directions, namely the X direction and the Y direction. The magnets indicated by grey squares have an opposite magnetic polarization compared to the magnets indicated by white squares.

[0032] Planar motor 200 further comprises a mover 220 having coil assemblies 220.1, 220.2, 220.3, and 220.4 configured to generate forces in both the X and Y directions by providing appropriate currents to the coils or coil sets 220.1, 220.2, 220.3, and 220.4 of the coil assemblies. In the illustrated embodiment, each coil set comprises three coils that can be powered, for example, by a three-phase power source. Note that magnet assembly 210 of planar motor 200 may also be referred to as the stator of the motor, although magnet assembly 210 need not be configured to remain stationary. Specifically, magnet assembly 210 may be arranged as a balance mass.

[0033] As an alternative to the use of permanent magnets to generate the magnetic field distribution required to operate a planar electromagnetic motor such as planar motor 200, the use of superconducting (SC) coils has been proposed. In such an embodiment, circular or cylindrical coils may function to generate a magnetic field along the axial direction of the coils when current is applied to the coils. By appropriate arrangement of the coils and applied current, a magnet assembly can be obtained that, in use, generates a two-dimensional spatially alternating magnetic field similar to that generated by magnet assembly 210 shown in FIG. 4. FIG. 5 schematically illustrates a top view of a two-dimensional (2D) array 300 of superconducting (SC) coils 310 that, when powered, can generate a two-dimensional spatially alternating magnetic field. Arrows 320 within the SC coils 310 indicate the direction of current flow through the SC coils 310.

[0034]

[0032] Figure 6 shows a schematic top view of a planar motor 600 having a stator array of superconducting coils 610 configured to generate a two-dimensional spatially alternating magnetic field. In the illustrated arrangement, the direction of current flow in the black coils 610.1 is opposite to the direction of current flow in the white coils 610.2. This allows the generation of a two-dimensional spatially alternating magnetic field. The planar motor 600 also includes a mover 620. In the illustrated arrangement, the mover has a structure similar to the mover 220 shown in Figure 4. Specifically, the mover includes a coil assembly including coils or coil sets 620.1, 620.2, 620.3, and 620.4, which are configured to generate forces in both the X and Y directions by providing appropriate currents to the coils or coil sets 620.1, 620.2, 620.3, and 620.4 of the coil assembly. It can also be noted that the set of currents supplied to the coil sets can be configured to control the positioning of the mover relative to the array of superconducting coils 610 in six degrees of freedom.

[0035]

[0033] Figure 7 schematically illustrates a cross-sectional side view of the planar motor 600 of Figure 6. In Figure 7, arrows 710 and 720 indicate force components of a force generated when appropriate currents are supplied to the coils or coil sets of the mover 620. Specifically, the generated force may comprise, for example, a vertical component 710 to suspend the mover 620 relative to the stator 610, i.e., the array of superconducting coils 610, and a horizontal component 720 to displace the mover 620 in a horizontal plane, i.e., the XY plane, relative to the stator 610. In the illustrated arrangement, the 2D array of superconducting coils 610 is disposed within a cryostat 730 configured to maintain the superconducting coils 610 in a superconducting state.

[0036] When such a planar motor 600 is applied in a lithography apparatus, it is necessary to ensure that the magnetic field generated by the 2D array of SC coils 610 is maintained, for example, to achieve accurate positioning of the mover 620 holding the substrate 622. It has been observed that the mover's energized coils can induce losses in the superconducting coils of the 2D array of SC coils 610. This loss can be attributed to magnetic field changes experienced by the 2D array of SC coils 610, which can result from movement of the mover's energized coils relative to the stator's 2D array of SC coils 610, or from current changes or transients in the coils of the mover 620. Due to this loss, there is a risk that one or more coils of the 2D array of SC coils 610, or even part of one coil, will transition from a superconducting state to a normal conducting state. Such a transition can also be referred to as a quench. According to the present invention, measures are proposed to reduce or mitigate the risk of such a quench occurring during motor operation. Specifically, the present invention proposes disposing a shield configured to mitigate magnetic field changes experienced by the 2D array of SC coils 610 upon displacement of a mover of a planar motor relative to the 2D array of SC coils 610.

[0037] FIG. 8 shows a schematic cross-sectional view of a planar motor 800 according to the present invention, which includes a magnet assembly 810 according to the present invention. In the illustrated embodiment, the magnet assembly 810 includes a 2D array of superconducting (SC) coils 810.1 and a shield 810.2. In the illustrated embodiment, both the 2D array of SC coils 810.1 and the shield 810.2 are disposed within a cryostat 830. Depending on the material used for the shielding layer, it may also be possible to dispose the shield outside the cryostat, for example on the outer surface of the cryostat. In one embodiment, the 2D array of SC coils 810.1 may be a two-dimensional array of circular or cylindrical coils, as shown in FIGS. 5 and 6. According to the present invention, the 2D array of SC coils 810.1 of the magnet assembly 810 is configured to generate a spatially alternating magnetic field in two dimensions. Such a magnetic field can be realized by supplying an appropriate current, typically a DC current of several kA, to the 2D array of SC coils 810.1 of the magnet assembly. The generated magnetic field typically extends beyond the top surface 830.1 of the cryostat 830 and will have a magnitude superior to that of magnetic field strengths generated using permanent magnets. In the illustrated embodiment, the planar motor 800 further includes a mover 840 configured to displace relative to the magnet assembly 810, e.g., in six degrees of freedom. To do so, the mover 840 may include, e.g., one or more coil sets. When current is applied to these coil sets, forces are generated by the interaction between the currents supplied to the mover coils and the magnetic field of the magnet assembly 810. When the mover 840 moves relative to the magnet assembly 810, or when current changes or transients occur in one or more coils of the mover 820, the 2D array of SC coils 810.1 may experience changes in magnetic field strength. In the present invention, a shield 810.2 is applied to mitigate the adverse effects of such magnetic field changes. In accordance with the present invention, shield 810.2 is positioned on the side of the 2D array of SC coils 810.1 that, during use, faces mover 840 of planar motor 800. In the illustrated embodiment, mover 840 is positioned above magnet assembly 810.Thus, in such an embodiment, shield 810.2 may be positioned above the 2D array of SC coils 810.1, i.e., between the 2D array of SC coils 810.1 and mover 840. In the illustrated embodiment, the shield extends over substantially the entire area covered by the 2D array of SC coils 810.1. In an alternative embodiment, shield 810.2 may be positioned between or below the 2D array of SC coils 810.1.

[0038] In accordance with the present invention, the shield comprises a layer of conductive material that substantially covers the area covered by the 2D array of SC coils 810.1 of the magnet assembly 810. In accordance with the present invention, the layer of conductive material further has a thickness variation across the area, the thickness variation being related to the geometric parameters of the 2D array of SC coils.

[0039] In one embodiment, the layer of conductive material may be a layer of superconducting (SC) material.

[0040]

[0038] When the shield according to the present invention is applied to a superconducting magnet assembly for a planar motor, it can mitigate the adverse effects of magnetic field changes experienced by an array of SC coils. This may be understood as follows.

[0041]

[0039] When the energized coils of mover 840 cause magnetic field changes near the 2D array of SC coils 810.1, the layer of conductive material of shield 810.2 also experiences these magnetic field changes. Specifically, the magnetic field changes induce currents or current distributions in the layer of conductive material, optionally the layer of SC material, of shield 810.2. This current or current distribution results in a magnetic field that opposes or cancels the magnetic field changes. As a result, the 2D array of SC coils 810.1 experiences lower magnetic field changes. As a result, fewer losses are induced in the 2D array of SC coils, thus reducing the risk of quenching one or more coils in the 2D array of SC coils. It can also be noted that lower losses in the 2D array of SC coils can maintain lower temperatures in the SC coils, resulting in lower cooling costs. This can also make the SC magnet assembly more robust.

[0042]

[0040] Improved control of the induced magnetic field within the shield can be obtained by introducing variations in the thickness of the layer of conductive material within the shield.

[0043] In one embodiment, the planar motor 800 according to the present invention further comprises a first power supply P1 for powering the 2D array of SC coils 810.1 and a second power supply P2 for powering one or more coil sets of the mover 840 of the planar motor 800. In one embodiment, the first power supply P1 may be configured, for example, to provide DC current to the 2D array of SC coils 810.1 of the magnet assembly 810 of the planar motor 800. The second power supply P2 may be configured, for example, to provide AC current, for example, a set of three-phase currents, to one or more coil sets of the mover 840 of the planar motor 800. The planar motor according to the present invention may further comprise a control unit CU for controlling the power supplies P1 and P2.

[0044]

[0042] In the following, further details are provided about various embodiments of the shielding applied in the superconducting magnet assembly according to the present invention, in particular about the variations in the thickness applied.

[0045] In one embodiment of the present invention, the thickness variation applied to the layer of conductive material spans a thickness between the nominal thickness and zero. In other words, the layer of conductive material need not be a continuous layer of material spanning the area covered by the 2D array of SC coils 810.1. Rather, certain parts or portions of the shield may be free of conductive material. Alternatively, certain areas or portions may be layers of conductive material having a reduced thickness or a thickness less than the nominal thickness.

[0046] In one embodiment, the thickness variations of the layers of conductive material of shield 810.2 comprise a repeating pattern. Such a repeating pattern may have a periodicity related to, for example, a geometric parameter of the 2D array of SC coils 810.1. The periodicity may be related, for example, to the pitch P of the 2D array of SC coils 810.1, where pitch P refers to the distance between adjacent coils in the 2D array of SC coils 810.1.

[0047] In one embodiment, the repeating pattern comprises a repeating pattern of geometric shapes, each geometric shape being associated with one SC coil in the 2D array of SC coils 810.1.

[0048] FIG. 9 schematically illustrates a patterned layer of conductive material that can be applied as a shield for a magnet assembly according to the present invention. In the illustrated embodiment, the layer of conductive material 900 comprises a pattern of circles 910, whereby each circle represents a circular-shaped layer of conductive material. The regions between the circles 910, i.e., regions 920, may be covered with a layer of conductive material having a different thickness or may be free of conductive material. It should be noted that in one embodiment of the present invention, the layer of conductive material is disposed on a support layer or support surface. If the layer of conductive material is made of a metal such as copper or aluminum, the support layer or support surface may be, for example, a plate made of a non-conductive material. If the layer of conductive material is made of a superconductive material, the support layer may be, for example, a thin metal plate, e.g., an aluminum or copper plate. It should be noted that such a conductive plate may also be patterned, i.e., the portions of the plate not covered by superconductive material may be at least partially removed to reduce the conductivity between the regions of superconductive material, e.g., between the patterns of circles 910. Alternatively, the support layer or support surface can be made of a non-conductive material. In one embodiment of the present invention, a layer of SC material can be disposed as a shield on a layer or surface of a cryostat. As an example, a patterned layer of SC material can be disposed on the inner surface of, for example, a cryostat top plate, which is disposed between, for example, a magnet assembly and a mover. Alternatively, or additionally, a patterned layer of conductive material, such as copper or aluminum, can be disposed on the outer surface of the cryostat top plate. In the illustrated embodiment, the dotted circle 930 represents the outer diameter of an SC coil, for example, of a 2D array of SC coils disposed beneath the shield or the layer of conductive material 900 of the shield. Thus, in the illustrated arrangement, the patterned layer of conductive material 900 comprises a plurality of circular shapes 910, each of which can be associated with one SC coil of the 2D array of SC coils of the magnet assembly in which the shield is used. In the illustrated arrangement, the circular shapes have a diameter somewhat smaller than the outer diameter of the associated SC coil.In the illustrated arrangement, the circular shapes 910 are also aligned with each SC coil of a 2D array of SC coils in the magnet assembly to which the shielding is applied.

[0049]

[0047] As will be appreciated, the application of circular shape 910 as a pattern in the layer of conductive material of the shield is just one example of a possible shape and pattern that can be applied and that allows control of the magnetic field induced within the shield due to magnetic field changes caused by movement of a mover relative to a magnet assembly comprising a 2D array of SC coils, e.g., coil 810.1.

[0050]

[0048] Figures 10a to 10c show schematically some further possible patterns of geometric shapes that can be applied to shape the layer of conductive material of the shield.

[0051]

[0049] Figure 10a shows a schematic diagram of another example of a pattern that can be applied to a layer of conductive material for a shield used in the present invention. The pattern comprises a plurality of squares 1010 configured to be aligned with a 2D array of SC coils. In Figure 10a, dotted outlines 1020 represent the outer diameters of the coils of such a 2D array of SC coils. As shown above, the areas outside the squares 1010 that form the pattern may be covered with a conductive material having a different thickness than the squares 1010, or may be free of conductive material.

[0052]

[0050] Figure 10b shows a schematic diagram of yet another example of a pattern that can be applied to a layer of conductive material for shielding used in the present invention. This pattern comprises a plurality of ring-shaped structures 1050 configured to be aligned with a 2D array of SC coils. In Figure 10b, dotted outlines 1060, 1065 represent the outer and inner diameters of the coils of such a 2D array of SC coils. In the illustrated arrangement, the ring-shaped structures 1050 have an outer diameter that is smaller than the outer diameter of the associated SC coil and an inner diameter that is larger than the inner diameter of the associated SC coil. Alternatives are possible in which the outer diameter of the ring-shaped structures 1050 substantially corresponds to the outer diameter 1060 of the SC coil, or in which the inner diameter of the ring-shaped structures 1050 is equal to or smaller than the inner diameter 1065 of the SC coil.

[0053]

[0051] Figure 10c shows a schematic diagram of yet another example of a pattern that can be applied to a layer of conductive material for a shield used in the present invention. The pattern comprises a plurality of strips 1070 made of conductive material, which are aligned with the pattern of a 2D array of SC coils of a magnet assembly. In Figure 10c, the dotted outline 1020 represents the outer diameter of the coils of such a 2D array of SC coils. In the illustrated arrangement, the strips are arranged in a woven manner. It can be noted that the strips do not have to be arranged in a woven manner. Instead, two sets of parallel strips arranged one on top of the other can also be applied.

[0054] As previously mentioned, in accordance with the present invention, the layer of conductive material of the shield applied in the magnet assembly has a thickness variation across the area that is related to the geometric parameters of the 2D array of SC coils, which, as explained above, may include one or more of the geometric parameters of the coils themselves, such as the pitch of the 2D array of SC coils or the inner or outer diameter of the SC coils.

[0055] In one embodiment, the thickness variation applied to the layer of conductive material may also depend on the distance between the 2D array of SC coils and the shield, such as the distance d shown in Figure 8. The thickness variation may also depend on the applied distance between the mover coils and the shield.

[0056] In one embodiment of the present invention, the SC magnet assembly includes two or more shields. In one embodiment, the SC magnet assembly includes multiple shields, each with a different pattern or thickness variation. Such an embodiment may provide even greater design freedom in shaping the induced magnetic field that counteracts magnetic field variations.

[0057]

[0055] The planar motor according to the present invention may be advantageously applied in the lithographic apparatus according to the present invention, in particular, the planar motor may be applied, for example, as the second positioner PW described above.

[0058]

[0056] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein have other applications, such as in 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.

[0059] Although specific reference is made herein to embodiments of the invention in relation to lithography apparatus, embodiments of the invention may also 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 objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus are sometimes referred to generically as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0060]

[0058] Although the above makes particular reference to the use of embodiments of the present invention in connection with optical lithography, it will be understood that the present invention may also be used in other applications, such as imprint lithography, and is not limited to optical lithography, where the context permits.

[0061] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present 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, machine-readable media may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing particular actions. However, it should be understood that such description is merely for convenience and that such actions actually result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., and that, in performing these actions, actuators or other devices may interact with the physical world.

[0062]

[0060] While specific embodiments of the present invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is intended to be illustrative and not limiting. Accordingly, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. 1. A superconducting (SC) magnet assembly for a planar motor, comprising: a two-dimensional (2D) array of SC coils configured to generate a two-dimensional spatially alternating magnetic field; a shield disposed on a side of the 2D array of SC coils facing a mover of the planar motor during use, the shield being configured to mitigate magnetic field changes experienced by the 2D array of SC coils; the shield comprises a layer of conductive material; the layer extends over an area substantially covering the 2D array of SC coils; the layer of conductive material has a thickness variation across the region; A superconducting magnet assembly, wherein the thickness variation across the region is related to a geometric parameter of the 2D array of SC coils.

2. 2. The superconducting (SC) magnet assembly of claim 1, wherein the magnetic field change is caused by a displacement of the mover of the planar motor relative to the 2D array of SC coils or by a current change or current transient in a coil or coil set of the mover.

3. 3. The superconducting (SC) magnet assembly of claim 1 or 2, wherein the thickness variation ranges between a nominal value and zero thickness.

4. 4. A superconducting (SC) magnet assembly according to claim 1, wherein the thickness variations of the layer of conductive material comprise a repeating pattern.

5. 5. The superconducting (SC) magnet assembly of claim 4, wherein the repeating pattern comprises a repeating pattern of geometric shapes, each geometric shape being associated with one SC coil in the array of SC coils.

6. The superconducting (SC) magnet assembly of claim 5 , wherein the geometric shape comprises a circle or a square.

7. 7. A superconducting (SC) magnet assembly according to claim 1, wherein the layer of conductive material comprises a layer of superconducting material.

8. 3. The superconducting (SC) magnet assembly of claim 1 or 2, wherein the layer of conductive material comprises a plurality of conductive or superconducting (SC) strips arranged in a weave pattern.

9. 9. The superconducting (SC) magnet assembly of claim 1, wherein the geometric parameter comprises a magnetic pitch of the array of SC coils, an inner diameter of a coil of the array of SC coils, or an outer diameter of a coil of the array of SC coils.

10. 10. A superconducting (SC) magnet assembly according to any one of claims 1 to 9, wherein the layer of conductive material is disposed on a non-conductive layer or surface.

11. the layer of conductive material comprises a layer of superconducting (SC) material; 11. A superconducting (SC) magnet assembly according to any one of claims 1 to 10, wherein the layer of superconducting (SC) material is disposed on a non-conducting or conductive layer or surface.

12. further comprising a cryostat; 12. The superconducting magnet assembly of claim 1, wherein the 2D array of SC coils is disposed inside the cryostat.

13. 13. The superconducting magnet assembly of claim 1, wherein the shield is disposed inside the cryostat.

14. 14. The superconducting magnet assembly of claim 13, wherein the cryostat is configured to cool the 2D array of SC coils and the shield to a superconducting state during operation.

15. 15. The superconducting magnet assembly of claim 13 or 14, wherein the shield is disposed on an inner or outer surface of the cryostat disposed between the 2D array of SC coils and the mover.

16. 15. A superconducting magnet assembly according to claim 13 or 14, wherein the shield is at least partially disposed between the 2D array of SC coils.

17. 1. A planar motor for use in a lithographic apparatus, comprising: A superconducting magnet assembly according to any one of claims 1 to 16, and a mover, A planar motor, wherein the mover comprises one or more coil sets configured, in use, to cooperate with the magnetic field of the 2D array of SC coils of the superconducting magnet assembly.

18. 18. The planar motor of claim 17, comprising: a first power supply for powering the 2D array of SC coils; and a second power supply for powering the one or more coil sets of the mover.

19. A lithographic apparatus comprising a planar motor according to claim 17 or 18 for positioning a substrate.

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