Patent Publication Number: US-2023161271-A1

Title: Assembly Comprising a Cryostat and Layer of Superconducting Coils and Motor System Provided With Such an Assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is Divisional of U.S. Application No. 15/734,882, filed on Dec. 3, 2020, which is a 371 National Stage Entry of PCT/EP2019/061897, filed on May 9, 2019, which claims priority of EP application 18175898.8 which was filed on Jun. 5, 2018 and which is incorporated herein in its entirety by reference. 
    
    
     FIELD 
     The present invention relates to an assembly for use in a magnetic levitation and/or acceleration motor system of a lithographic apparatus. The assembly comprising a cryostat and a layer of superconducting coils. 
     BACKGROUND 
     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). 
     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. 
     In a lithographic apparatus a patterning device is subjected to a radiation beam. Whilst passing through the patterning device, a pattern is imparted to this radiation beam. Subsequently, the radiation beam with imparted pattern passes through a projection system, which projects the imparted pattern onto a substrate. In order to provide the substrate with a desired pattern, both the patterning device and the substrate are moved with respect to the projection system as well as with respect to each other. For this purpose linear and/or planar motor systems are used based on current conducting coils and permanent magnets at room temperature or higher due to heat developed by the coils. Linear and planar motor systems typically have a stator part and a mover part which is movable in controlled manner with respect to the stator part by manipulating the current through the current conducting coils. 
     SUMMARY 
     Analytical relations show that the magnetic field density in the coils of the mover of a linear or planar motor system can be improved a factor 4-5 by using superconducting electromagnets at a temperature of 4 K. In practise superconductors are available which are superconducting at higher cryogenic temperatures in the range of 70 K to 150 K. In order to put this superconducting electro magnets into practice a thermal insulation from the cryogenic temperature required to room temperature is needed which has to fit within a small stack height. Otherwise the distance between the coils of the mover and the superconducting magnets increases due to the insulation to an extent that the increase of magnetic field density in the coils is lost. There is therefore a need for a thermal insulation layer of small height. 
     Linear and planar motor systems used in a lithographic apparatus are typically used based on current conducting coils and magnets. Linear and planar motor systems used in a lithographic apparatus further typically have a stator part and a mover part which is movable in controlled manner with respect to the stator part by manipulating the current through the current conducting coils. It is realized that a) the magnets can be provided in the stator part and the current conducting coils in the mover part or, the other way around, the magnets can be provided in the mover part and the current conducting coils in the stator part, on the one hand, and that b) not only the magnets may be superconducting magnets having superconducting coils but additionally or alternatively the current conducting coils may be superconducting coils, on the other hand. 
     Taking all this into account, the present invention has as its object to provide an assembly comprising a cryostat and a coils layer of superconducting coils, the coil layer being flat and configured for use in or with a magnetic levitation and/or acceleration motor system of a lithographic apparatus. 
     According to a first aspect of the invention, there is provided an assembly comprising a cryostat and a coil layer of superconducting coils, wherein the coil layer is configured for use in or with a magnetic levitation and/or acceleration motor system of a lithographic apparatus, is flat and defines two opposing layer faces. 
     The coil layer may be configured as a stator part of a magnetic levitation and/or acceleration motor system and/or as a mover part of a magnetic levitation and/or acceleration motor system. Further the coil layer may be wired for alternating current operation and/or may be an array of electromagnets wired for direct current operation. 
     The magnetic levitation and/or acceleration motor system may be a linear motor system or a planar motor system. 
     The cryostat comprises two insulation coverings. The coil layer and two insulation coverings are arranged in a sandwich manner, with the coil layer arranged between the two insulation coverings and each of the two opposing layer faces of the coil layer covered by one of the insulation coverings in order to be able to keep the coil layer at a cryogenic condition required superconductivity of the coils. 
     The insulation coverings each comprise: an inner plate and an outer plate parallel to the inner plate, the inner plate being arranged between the outer plate and the coil layer, and an insulation system arranged between the inner plate and the outer plate. The inner plate and/or outer plate may be from a stainless steel alloy. 
     The insulation system is configured to have a vacuum layer. A vacuum layer in the insulation system reduces the thermal conductivity between the inner plate and outer plate. This vacuum may be a vacuum of 10 -3  Pa or lower. When the mover is in an ambient of normal air pressure, this results in that the insulation covering has to be able to withstand a pressure difference of 1 bar. Taking into account that in planar motor systems for moving the substrate in a lithographic apparatus, the stator typically has a surface in the order of 1 meter by 2 meter, or larger, this means that the thermal insulation must be able to withstand large forces. 
     The inner plates are configured for being cryocooled in order to bring and maintain the coil layer at cryogenic condition. 
     The insulation system of one or both said insulation coverings:
     comprises, in the vacuum layer, one or more layers of at least partly circular bodies each defining an at least partly circular contour and a central axis extending through a center of the circular contour as well as perpendicular to the circular contour, the central axes of the bodies of each layer of circular bodies extending perpendicular to the inner and outer plate, and   is configured to provide at least one layer of point contacts between two said layers of circular bodies or between a said layer of circular bodies and the inner and/or outer plate such that each possible thermal conductive path between the inner and outer plate has to pass, at some place, through at least one point contact.   
 The layers of circular bodies are arranged between the inner and outer plate and support the inner plate on the outer plate - when the inner plate lies above the outer plate - or the outer plate on the inner plate - when the outer plate lies above the inner plate -. Circular bodies have a high load-bearing capacity, on the one hand, whilst providing a point contact, on the other hand. As a point contact has a very small contact surface, the thermal conductivity through the point contact is very low. With one or more layers of circular bodies having their central axes perpendicular to the inner and outer plate and configured to provide at least one layer of point contacts it is ensured that each possible thermal conductive path between the inner and outer plate has to pass, at some place, through at least one point contact. This results in an insulation covering having minimal thermal conductivity, on the one hand, and high load bearing capacity on the other hand.
     The circular bodies may be fully circular or partly circular having a partly circular contour extending over an angle of 180° or less, like 60-120°. The circular bodies may be spherical bodies, like spheres and/or half-spheres, and/or straight cylindrical bodies, like cylinders and/or half-cylinders. For example, in case of half-spheres or half-cylinders, the half-spheres respectively half-cylinders may be glued onto the face of the inner plate facing the outer plate and/or onto the face of the outer plate facing the inner plate, and stacked onto each other resulting in a said layer of point contacts between half-spheres, between half-cylinders, or between half-spheres and half-cylinders. 
     Defining the diameter of a said circular body as twice the radius from the center of the circular contour to the circular contour, the diameter of the at least partly circular bodies may, according to a further embodiment, be smaller than 7 mm, such as smaller than 5 mm. The diameter may be in the range of 0.1 to 5 mm, such as in the range of 0.5 to 4 mm. Circular bodies with such a diameter are readily available, for example as spheres for ball bearings or as cylinders for needle bearings or as wires. Further, circular bodies of such diameter allow insulation coverings with a thickness - perpendicular to the inner and outer plate - of less than 10 mm. Even a thickness much lower is possible and/or multiple layers of point contact are possible with smaller diameters whilst still keeping the total thickness of the insulation covering below 10 mm. The thickness may for example be at most 7-8 mm. 
     The point contacts, in a said layer of point contacts, may, according to a further embodiment, be arranged with a pitch of 5-20 mm, for example a pitch of 10-15 mm. 
     According to an embodiment of the assembly, the circular bodies may be made from a material chosen from one or more of the group of: zirconia, Kevlar, Kevlar composites, Kevlar fiber composites, glass, glass composites, glass fiber composites, and titanium alloys. These materials are commercially available in the form of wires and spheres, have a large strength and low thermal conductivity. 
     According to an embodiment of the assembly, the circular bodies may be made from a material having a ratio of the Young modulus with respect to the integral of the thermal conductivity coefficient over the temperature range of 4 K to 80 K, which is at least 1 N/Wm, such as at least 1.5 N/Wm. Expressed in a formula, this ratio is: 
     
       
         
           
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                       λ 
                       
                         T 
                       
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             ≥ 
             1 
               
             N/Wm, 
           
         
       
     
      such as 
     
       
         
           
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                         80 
                       
                     
                     
                       λ 
                       
                         T 
                       
                       dT 
                     
                   
                 
               
             
             ≥ 
             1 
              N / Wm &gt; 1 
             .5 N/Wm 
           
         
       
     
     According to a further embodiment of the assembly, at least one said layers of spherical bodies may comprise spheres and a spacer plate provided with a pattern of circular through holes for accommodating the spheres, each through hole having a diameter configured to contact a said sphere such that the spacer plate is supported by the spheres, wherein the spacer plate is arranged parallel to the inner plate and outer plate. Viewed perpendicular to the spacer plate, the spacer plate is arranged at a distance from each of opposing ends of the spheres. This spacer plate prevents the spheres from rolling away by keeping them at locations determined by the through holes. In this embodiment the spacer plate may be configured for being cooled, like cryocooled, at a temperature between a temperature of the inner plate and a temperature of the outer plate. The spacer plate than additionally serves as insulation shield increasing the thermal insulation considerable. The diameter of the through holes may in this embodiment for example be in the range of 70-100%, such as 90-100%, of the diameter of the spheres. Further, in this embodiment, the thermal expansion coefficient of the spacer plate may be larger than the thermal expansion coefficient of the spheres such that when the spacer plate and spheres are cooled down a shrunk connection between the spacer plate and spheres is obtained in the through holes. This shrunk connection may provide a sealing closing the through hole with respect to the sphere, which improves the insulation capacity of the insulation system. For this purpose, the spacer plate may be made from aluminum or an aluminum alloy. 
     According to a further embodiment of the assembly, the assembly may comprise a multiple of said layers of spherical bodies, wherein between adjacent ones of said layers of spherical bodies a separation plate is arranged which provides on each side an additional layer of point contacts between the separation plate and spherical bodies. In this embodiment, the separation plate may be configured for being cooled, like cryocooled, at a temperature between a temperature of the inner plate and a temperature of the outer plate. 
     According to another further embodiment of the assembly, said one or more layers of circular bodies may comprise at least one set of two layers of straight cylindrical bodies, such as cylinders and/or half-cylinders; wherein the cylindrical bodies of a first of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies and the cylindrical bodies of a second of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies; and wherein the first layer and second layer are stacked directly onto each other with the cylindrical bodies of the first layer crosswise with respect to the cylindrical bodies of the second layer to provide, between the cylindrical bodies of the first layer and the cylindrical bodies of the second layer, a said layer of point contacts. In this embodiment, the cylindrical bodies may be wires. Crosswise may be at an angle of 90° or at any other angle, like an angle in the range of 30° to 90°, for example an angle of about 60°. 
     According to a further embodiment of the assembly, the assembly may further comprise a cryocooler system configured for cryocooling the inner plates. 
     According to a further embodiment of the assembly, the assembly may further comprise a vacuum system configured to provide in the vacuum layer a vacuum of 10 -3  Pa or lower. 
     According to a further aspect, the invention relates to a lithographic apparatus provided with an assembly according to the invention. Such a lithographic apparatus may comprise a mask support constructed to support a patterning device, a first positioner configured to position the mask support with respect to the first positioner, a substrate support constructed to hold a substrate, a second positioner configured to position the substrate support with respect to the second positioner, and a projection system configured to project a pattern imparted to a radiation beam by the patterning device onto a target position on the substrate; wherein one or more of the items ‘the mask support, the first positioner, the substrate support, and the second positioner’ are provided with an assembly according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: 
         FIG.  1    depicts a schematic overview of a lithographic apparatus; 
         FIG.  2    depicts a detailed view of a part of the lithographic apparatus of  FIG.  1   ; 
         FIG.  3    schematically depicts a position control system; 
         FIG.  4    schematically depicts a cross section of a planar motor system provided with an embodiment of the assembly according to the invention; 
         FIG.  5    schematically depicts in top view a planar motor system; 
         FIG.  6    schematically depicts a second embodiment of an insulation covering of an assembly according to the invention; 
         FIG.  7    schematically depicts a third embodiment of an insulation covering of an assembly according to the invention; and 
         FIG.  8    schematically depicts a detail of a fourth embodiment of an insulation covering of an assembly according to the 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. 
       FIG.  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. 
     The assembly according to the invention - which will be elucidated further below -may be used in the first positioner PM and/or mask support MT. Further, in addition or alternatively the assembly according to the invention - which will be elucidated further below - may be used in the second positioner PW and/or substrate support WT. 
     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. 
     The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection systems, 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. 
     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. 
     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. Also in case of two or more substrate supports WT, the assembly according to the invention - which will be elucidated further below - may be used in the second positioner PW and/or the two or more substrate supports. 
     In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor and/or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS. 
     In operation, the radiation beam B is incident on the patterning device, e.g. mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system PMS, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in  FIG.  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 M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks P1, P2 are known as scribe-lane alignment marks when these are located between the target portions C. 
     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 x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane. 
       FIG.  2    shows a more detailed view of a part of the lithographic apparatus LA of  FIG.  1   . The lithographic apparatus LA may be provided with a base frame BF, a balance mass BM, a metrology frame MF and a vibration isolation system IS. The metrology frame MF supports the projection system PS. Additionally, the metrology frame MF may support a part of the position measurement system PMS. The metrology frame MF is supported by the base frame BF via the vibration isolation system IS. The vibration isolation system IS is arranged to prevent or reduce vibrations from propagating from the base frame BF to the metrology frame MF. 
     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. 
     In an embodiment, the second positioner PW is supported by the balance mass BM. For example, wherein the second positioner PW comprises a part of a planar motor system to levitate or accelerate the substrate support WT above and/or relative to the balance mass BM. This planar motor system may be a magnetic levitation and/or acceleration motor system provided with an assembly according to the invention - which will be elucidated further below -. In another embodiment, the second positioner PW is supported by the base frame BF. For example, wherein the second positioner PW comprises a stator of 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. According to another example, the second positioner may comprise a linear motor system provided with an assembly according to the invention - which will be elucidated further below -. 
     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. 
     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 Sep. 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,+1 st  order, -1 st  order, +2 nd  order and -2 nd  order. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines a phase or phase difference of the combined radiation beam. The sensor generates a signal based on the phase or phase difference. The signal is representative of a position of the encoder head relative to the grating. One of the encoder head and the grating may be arranged on the substrate structure WT. The other of the encoder head and the grating may be arranged on the metrology frame MF or the base frame BF. For example, a plurality of encoder heads are arranged on the metrology frame MF, whereas a grating is arranged on a top surface of the substrate support WT. In another example, a grating is arranged on a bottom surface of the substrate support WT, and an encoder head is arranged below the substrate support WT. 
     The position measurement system PMS may comprise an interferometer system. An interferometer system is known from, for example, U.S. Pat. US6,020,964, filed on Jul. 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. 
     The first positioner PM may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT relative to the long-stroke module with a high accuracy over a small range of movement. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS with a relatively low accuracy over a large range of movement. With the combination of the long-stroke module and the short-stroke module, the first positioner PM is able to move the mask support MT relative to the projection system PS with a high accuracy over a large range of movement. Similarly, the second positioner PW may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the substrate support WT relative to the long-stroke module with a high accuracy over a small range of movement. The long-stroke module is arranged to move the short-stroke module relative to the projection system PS with a relatively low accuracy over a large range of movement. With the combination of the long-stroke module and the short-stroke module, the second positioner PW is able to move the substrate support WT relative to the projection system PS with a high accuracy over a large range of movement. 
     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 of the first positioner and/or second positioner may be a linear actuator to provide a driving force along a single axis, for example the y-axis. This linear actuator may be provided with an assembly according to the invention. Multiple linear actuators, which may be provided with an assembly according to the invention, 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. This planar actuator may be provided with an assembly according to the invention. For example, the planar actuator may be arranged to move the substrate support WT in 6 degrees of freedom. The actuator may be an electro-magnetic actuator comprising at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying an electrical current to the at least one coil. The actuator may be a moving-magnet type actuator, which has the at least one magnet coupled to the substrate support WT respectively to the mask support MT. The actuator may be a moving-coil type actuator which has the at least one coil coupled to the substrate support WT respectively to the mask support MT. The actuator may be a voice-coil actuator, a reluctance actuator, a Lorentz-actuator or a piezo-actuator, or any other suitable actuator. 
     The lithographic apparatus LA comprises a position control system PCS as schematically depicted in  FIG.  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. 
       FIG.  4    shows, schematically, a side cross-section of magnetic levitation and/or acceleration motor system  1  according to the invention, which system has a flat coil layer  3   of electromagnets  2  and is provided with an assembly  6 ,  7 ,  8 ,  9  according to the invention. Due to the coil layer  3  being flat, this magnetic levitation and/or acceleration motor system  1  is a linear motor system or planar motor system. The coil layer  3  is flat, because the electromagnets  2  are arranged in a plane. In the example of  FIG.  4   , it is a planar motor system. In the example shown, this planar motor system  1  is used in the wafer stage of a lithographic apparatus. For this purpose, the substrate W, substrate support WT and second positioner PW are indicated with the same references as used in  FIGS.  1 - 3   . In addition or alternatively, the magnetic levitation and/or acceleration motor system  1  according to the invention may also be used as a planar or linear motor system in the mask stage of a lithographic apparatus, in which case the substrate W may be the patterning device MA (e.g. a mask), the substrate support WT may be the mask support MT and the second positioner PW may be the first positioner PM. 
       FIG.  5    shows a detail of  FIG.  4   , which details are shown in  FIG.  4    in cross-section according the arrows IV as indicated in  FIG.  5   . 
     In the embodiments of  FIGS.  4  and  5    the assembly according to the invention is provided in the stator part of the planar motor system  1 . The mover part of this planar motor system, in this example indicated as WT, is at its underside provided with a flat layer of conducting coils  21 ,  22  in which the current can be manipulated by means of a controller in order to control the position of the mover part WT with respect to the stator part PW;  8 ,  3 ,  9 . 
     The assembly according to the invention comprises a cryostat  6 ,  7 ,  8  and  9  configured to cryocool the superconducting electromagnets  2  in the coil layer  3  at a cryogenic temperature, for example a temperature below 30 K as indicated in  FIG.  4   . Taking into account that presently there are materials available which are superconducting in the range of 70 K to 150 K, this temperature may also be higher than 30 K. 
     In the embodiments of  FIGS.  4  and  5   , the coil layer  3  is a layer of superconducting electromagnets  2 . The coil layer is flat and has opposing layer faces  4 ,  5 . In  FIG.  4   , layer face  4  is the lower face of the coil layer  3  and layer face  5  is the upper face of coil layer  3 . 
     The cryostat comprises a cryocooler system  6 , a vacuum system  7 , and two insulation coverings  8 ,  9 . The coil layer  3  and two insulation coverings  8 ,  9  are arranged in a sandwich manner, with the coil layer  3  arranged between the two insulation coverings  8 ,  9  such that each of the two opposing layer faces  4 ,  5  is covered by one of the insulation coverings  8 ,  9 . 
     One of the insulation coverings or both the insulation coverings  8 ,  9  may each comprise an inner plate  10  and an outer plate  11  parallel to the inner plate  10 . The inner plate  10  is closest to the coil layer  3  and arranged between the outer plate  11  and the coil layer  3 . One of or both the insulation coverings  8 ,  9  may further comprise an insulation system  12  arranged between the inner plate  10  and outer plate  11 . 
     The vacuum system is configured to provide a vacuum (layer)  13  in the insulation system. 
     The cryocooler system is configured for cryocooling the inner plates  10  and is for this purpose at  14  connected with the inner plate  10  of the insulation covering  9 . Because the inner plate  10  of the insulation covering  8  is thermally connected with the inner plate  10  of the insulation covering  9 , also the inner plate  10  of the insulation covering will be cryocooled. This thermal connection may for example be provided via the magnets  2  or not shown thermal bridges. 
     According to the invention, the insulation system  12  of one or both said insulation coverings  8 ,  9  comprises, in the vacuum (layer)  13 , one or more layers of at least partly circular bodies  101  each defining an at least partly circular contour  102  and a central axis extending through a center  103  of the circular contour  102  as well as perpendicular to the circular contour  102 . The central axes of the circular bodies  101  of each layer of circular bodies extend perpendicular to the inner plate  10  and outer plate  11 . In the embodiment as shown in  FIG.  4   , the at least partly circular bodies are spheres, in this case full-spheres, but these circular bodies may also be half-spheres or straight cylindrical bodies, e.g. full-cylindrical bodies or half-cylindrical bodies. The term ‘full-’ relates specifically to the outer contour of the circular bodies not to the inner of the circular bodies. The inner of a full-circular bodies may for example be hollow or a full-circular body may have a through bore in order to save weight and/or to reduce the thermal conductivity of the bodies. 
     The insulation covering  8 ,  9  according to the invention is furthermore configured to provide at least one layer  104 ,  105  of point contacts  106  between two said layers of circular bodies  101  or between a said layer of circular bodies  101  and the inner plate  10  and/or outer plate  11 . This configuration is such that each possible thermal conductive path between the inner plate  10  and outer plate  11  has to pass, at some place, through at least one point contact  106 . This results in an insulation covering having minimal thermal conductivity due to the layer of point contacts, on the one hand, and high load bearing capacity due to the at least partly circular bodies on the other hand. In the example of  FIG.  4   , there are two layers  104  and  105  of point contacts  106 . One layer  105  at the side of the outer plates  11  and one layer  104  at the side of the inner plates. 
     In the embodiment of  FIG.  4   , the circular bodies  101  may be (full-)spheres of zirconium with a diameter of 7 mm. These spheres lie between the inner plate  10  and outer plate  11 . In a linear motor the vertical distance D between the layer  3  of electro-magnets  2  and the conducting coils  21 ,  22  is limited. This means that the vertical thickness (in the direction of double arrow D) of especially the insulation covering  8  is to be kept low. With an aluminum inner plate  10  and aluminum outer plate  11  of each 0.75 mm thickness and spheres with a diameter of 7 mm, the total thickness of the insulation covering is about 9 mm. This thickness can easily be reduced by using a thinner inner plate  10  and thinner outer plate  11  and/or by using spheres  101  of smaller diameter. In this respect it is to be noted that zirconium spheres with diameters as from 0.2 mm can be readily obtained in the market against low prices. 
     Also the insulation covering  9  can be designed very thin, but taking into account that on this side of the layer  3  of superconducting electromagnets  2  space is in general not a real issue, the spheres  101  in the insulation covering  9  can be taken larger than the spheres  101  in the insulation covering  8 . The spheres in the insulation covering may for example be in the range of 15-20 mm. 
     In order to prevent these spheres from rolling away, a spacer plate  107  may be provided. This spacer plate  107  may be provided with a pattern of through holes, each having a diameter in the range of 70-100% of the diameter of the spheres. By using a spacer plate with a thermal expansion coefficient larger than the thermal expansion coefficient of the spheres, a sealing shrunk connection between the spheres  101  and spacer plate  107  is obtained when the inner plate is cryocooled. Further, the spacer plate  107  may be kept at a temperature of in this example about 80 K by the crycooler. For this purpose the crycooler  6  is at  108  connected with the spacer plate  107  of the insulation covering  9  (and/or  8 , not shown). The spacer plate  107  then serves as a shield which improves the insulation capacity of the insulation covering  8 ,  9 . In order to cool both the spacer plates  107 , the spacer plates  107  are thermally connected by thermal connection  109 . 
     As shown in  FIG.  4    by means of the indicated temperatures, the substrate support WT may be at room temperature, the coils  21  and  22  may have a temperature higher than room temperature due to heat development in the coils  21  and  22 , and the frame  15  may be at room temperature as well. Further the crycooler cryocools both the inner plates  10  at a cryogenic temperature, which will, according to this example, be below 30 K. To improve the insulation, the spacer plates  107  are cooled by the cryocooler to have a temperature between the temperature of the inner plates (in this example &lt; 30 K) and the temperature of the outer plates (in his example 295 K). The temperature of the spacer plates may for example be 80 K. 
     In the example of  FIGS.  4  and  5   , the planar motor system according to the invention has a stator part provided with a flat layer of superconducting electromagnets  2  and a mover part provided with a flat layer of normal-conducting coils  21 ,  22  (which are in general at room temperature or higher when, in use, the coils  21 ,  22  produce heat), see  FIGS.  4  and  5   . It is noted that additionally or alternatively the flat layer of coils  21  may, according to the invention, be a flat layer of superconducting coils having on both sides or one side of the flat layer an insulation covering  8 ,  9  according to the invention with at least partly circular bodies in a vacuum layer. In this case the coil layer  3  may be a coil layer of permanent magnets or normal electromagnets or superconducting electromagnets. 
     As shown in very schematic cross-section in  FIGS.  6  and  7   , the insulation covering  8  and/or insulation covering  9  may also comprise multiple layers of spheres, separated by intermediate plates. 
       FIG.  6    shows two layers  200 ,  210  of spheres  201  and  211 , respectively. The spheres  201  in the layer  200  may be maintained in position by a spacer plate  207  and the spheres  211  in the layer  210  may be maintained in position by a spacer plate  217 . The two layers  200  and  210  of spheres  201  and  211  may be separated by an intermediate layer  240 . This configuration provides a total of four layers  204 ,  205 ,  214  and  215  of point contacts  206  and  216 . By using spheres of smaller diameter, the thickness of the insulation covering of  FIG.  6    can still be maintained at or below the 9 mm thickness as mentioned in relation to  FIG.  4   . 
       FIG.  7    shows four layers  300 ,  310 ,  320 ,  330  of spheres  301 ,  311 ,  321  and  331 , respectively. The spheres  301  in the layer  300  may be maintained in position by a spacer plate  307 , the spheres  311  in the layer  310  may be maintained in position by a spacer plate  317 , the spheres  321  in the layer  320  may be maintained in position by a spacer plate  327 , and the spheres  331  in the layer  330  may be maintained in position by a spacer plate  337 . The two layers  300  and  310  of spheres  301  and  311  may be separated by an intermediate layer  340 , the two layers  310  and  320  of spheres  311  and  321  may be separated by an intermediate layer  350 , and the two layers  320  and  330  of spheres  321  and  331  may be separated by an intermediate layer  360 . This configuration provides a total of eight layers  304 ,  305 ,  314 ,  315 ,  324 ,  325 ,  334  and  335  of point contacts  206 ,  216 ,  226  and  236 . By using spheres of smaller diameter, the thickness of the insulation covering of  FIG.  7    can still be maintained at or below the 9 mm thickness as mentioned in relation to  FIG.  4   . 
     As shown in very schematic perspective view in  FIG.  8   , an insulation system providing at least one layer of point contacts can also be obtained with cross-wise stacked layers of straight cylindrical bodies, like the wires  401  and  402  having a circular circumference  402  respectively  412 . At the crossings of the wires  401  and  411  there will be point contacts  406 , as schematically indicated at four crossings in  FIG.  8   . In the construction of  FIG.  8   , the cylindrical bodies  401 ,  402  of each layer being straight and the layers being crosswise stacked ensured that each possible thermal conductive path between the inner and outer plate has to pass, at some place, through at least one point contact. 
     The present invention can also be characterized by the following clauses:
     1. An assembly comprising a cryostat and a coil layer of superconducting coils, 
   wherein the coil layer is configured for use in or with a magnetic levitation and/or acceleration motor system of a lithographic apparatus, is flat and defines two opposing layer faces;   wherein the cryostat comprises two insulation coverings;   wherein the coil layer is arranged between the two insulation coverings and each of the two opposing layer faces is covered by one of the insulation coverings;   wherein each said insulation covering comprises:
   an inner plate and an outer plate parallel to the inner plate, the inner plate being arranged between the outer plate and the coil layer, and   an insulation system arranged between the inner plate and the outer plate;   
   wherein the insulation system is configured to have a vacuum layer;   wherein the inner plates are configured to be cryocooled; and   wherein the insulation system of one or both said insulation coverings:
   comprises, in the vacuum layer, one or more layers of at least partly circular bodies each defining an at least partly circular contour and a central axis extending through a center of the circular contour as well as perpendicular to the circular contour, the central axes of the bodies of each layer of circular bodies extending perpendicular to the inner and outer plate, and   is configured to provide at least one layer of point contacts between two said layers of circular bodies or between a said layer of circular bodies and the inner and/or outer plate.   
   
   2. Assembly according to clause 1,
   wherein at least one said layer of circular bodies is a layer of spherical bodies, such as spheres or half-spheres.   
   3. An assembly comprising a cryostat and a coil layer of superconducting coils, 
   wherein the coil layer is configured for use in or with a magnetic levitation and/or acceleration motor system of a lithographic apparatus, is flat and defines two opposing layer faces;   wherein the cryostat comprises two insulation coverings;   wherein the coil layer is arranged between the two insulation coverings and each of the two opposing layer faces is covered by one of the insulation coverings;   wherein each said insulation covering comprises:
   an inner plate and an outer plate parallel to the inner plate, the inner plate being arranged between the outer plate and the coil layer, and   an insulation system arranged between the inner plate and the outer plate;   
   wherein the insulation system is configured to have a vacuum layer;   wherein the inner plates are configured to be cryocooled; and   wherein the insulation system of one or both said insulation coverings comprises, in the vacuum layer, one or more layers of spherical bodies, such as spheres or half-spheres, at least one said layers of spherical bodies providing a layer of point contacts between the layer of spheres and the inner and/or outer plate.   
   4. Assembly according to clause 2 or 3,
   wherein at least one said layers of spherical bodies comprises spheres and a spacer plate provided with a pattern of circular through holes for accommodating the spheres, each through hole having a diameter configured to contact a said sphere such that the spacer plate is supported by the spheres, wherein the spacer plate is arranged parallel to the inner plate and the outer plate.   
   5. Assembly according to clause 4,
   wherein the diameter of the through holes is in the range of 70-100%, such as 90-100%, of the diameter of the spheres.   
   6. Assembly according to one of clauses 4-5,
   wherein the spacer plate is configured to be cooled at a temperature between a temperature of the inner plate and a temperature of the outer plate.   
   7. Assembly according to one of clauses 4-6,
   wherein the thermal expansion coefficient of the spacer plate is larger than the thermal expansion coefficient of the spheres such that when the spacer plate and spheres are cooled down a shrunk connection between the spacer plate and spheres is obtained in the through holes.   
   8. Assembly according to one of clauses 4-7,
   wherein the spacer plate comprises aluminum or an aluminum alloy.   
   9. Assembly according to one of clauses 2-8, comprising a multiple of said layers of spherical bodies,
   wherein between adjacent ones of said layers of spherical bodies a separation plate is arranged which provides on each side an additional layer of point contacts between the separation plate and spherical bodies.   
   10. Assembly according to clause 9,
   wherein the separation plate is configured to be cooled at a temperature between a temperature of the inner plate and a temperature of the outer plate.   
   11. Assembly according to one of clauses 1-10,
   wherein said one or more layers of circular bodies comprise at least one set of two layers of straight cylindrical bodies, such as cylinders and/or half-cylinders;   wherein the cylindrical bodies of a first of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies and the cylindrical bodies of a second of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies; and   wherein the first layer and second layer are stacked directly onto each other with the cylindrical bodies of the first layer crosswise with respect to the cylindrical bodies of the second layer to provide, between the cylindrical bodies of the first layer and the cylindrical bodies of the second layer, a said layer of point contacts.   
   12. An assembly comprising a cryostat and a coil layer of superconducting coils, wherein the coil layer is configured for use in or with a magnetic levitation and/or acceleration motor system of a lithographic apparatus, is flat and defines two opposing layer faces,
   wherein the cryostat comprises two insulation coverings;   wherein the coil layer is arranged between the two insulation coverings and each of the two opposing layer faces is covered by one of the insulation coverings;   wherein each said insulation covering comprises:
   an inner plate and an outer plate parallel to the inner plate, the inner plate being arranged between the outer plate and the coil layer, and   an insulation system arranged between the inner plate and the outer plate;   
   wherein the insulation system is configured to have a vacuum layer;   wherein the inner plates are configured to be cryocooled; and   wherein the insulation system of one or both said insulation coverings comprises, in the vacuum layer, comprises at least one set of two layers of straight cylindrical bodies, such as cylinders and/or half-cylinders;   wherein the cylindrical bodies of a first of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies and the cylindrical bodies of a second of said two layers are arranged parallel to each other with a spacing between adjacent cylindrical bodies; and   wherein the first layer and second layer are stacked directly onto each other with the cylindrical bodies of the first layer crosswise with respect to the cylindrical bodies of the second layer to provide, between the cylindrical bodies of the first layer and the cylindrical bodies of the second layer, a layer of point contacts.   
   13. Assembly according to one of clauses 11-12,
   wherein the cylindrical bodies are wires.   
   14. Assembly according to one of the preceding clauses, 
   wherein the at least partly circular bodies have a diameter defined as twice a radius from a center of the circular contour to the circular contour; and   wherein the diameter is smaller than 7 mm, such as smaller than 5 mm.   
   15. Assembly according to clause 14,
   wherein the diameter is in the range of 0.1 to 5 mm, such as in the range of 0.5 to 4 mm.   
   16. Assembly according to one of the preceding clauses,
   wherein the point contacts, in a said layer of point contacts, are arranged with a pitch of 5-20 mm, such as a pitch of 10-15 mm.   
   17. Assembly according to one of the preceding clauses,
   wherein one of said insulation coverings has a thickness of at most 10 mm, such as at most 7-8 mm, the thickness being defined in a direction perpendicular to the inner and outer plate.   
   18. Assembly according to one of the preceding clauses,
   wherein the circular bodies are made from a material chosen from one or more of the group of:   zirconia, Kevlar, Kevlar composites, Kevlar fiber composites, glass, glass composites, glass fiber composites, and titanium alloys.   
   19. Assembly according to one of the preceding clauses, wherein the circular bodies are made
   from a material having a ratio of the Young modulus with respect to the integral of the thermal conductivity coefficient over the temperature range of 4 K to 80 K, which is at least 1 N/Wm, such as at least 1.5 N/Wm.   
   20. Assembly according to one of the preceding clauses, further comprising a cryocooler system configured for cryocooling the inner plates to a temperature lower than 30 K, such as lower than 10 K, like in the range of 0 - 4 K.   21. Assembly according to one of the preceding clauses, further comprising a vacuum system configured to provide in the insulation system a vacuum of 10 -3  Pa or lower.   22. Assembly according to one of the preceding clauses,
   wherein the inner and/or outer plate are made from a stainless steel alloy.   
   23. Assembly according to one of the preceding clauses,
   wherein the coil layer is configured as a stator part of the magnetic levitation and/or acceleration motor system.   
   24. Assembly according to one of the preceding clauses,
   wherein the coil layer is configured as a mover part of the magnetic levitation and/or acceleration motor system.   
   25. Assembly according to one of the preceding clauses,
   wherein the coil layer of super conducting coils is an array of superconducting electromagnets, each electromagnet having a north-south axis extending perpendicular to the coil layer;   wherein the array of electromagnets is configured such that adjacent electromagnets have opposite polarity; and   wherein the array of electromagnets is wired for direct current operation.   
   26. Assembly according to one of the preceding clauses,
   wherein the coil layer of superconducting coils is wired for alternating current operation.   
   27. Assembly according to one of the preceding clauses, wherein the magnetic levitation and/or acceleration motor system is a linear motor system.   28. Assembly according to one of the preceding clauses, wherein the magnetic levitation and/or acceleration motor system is a planar motor system.   29. A lithographic apparatus comprising at least one flat magnetic levitation and/or acceleration motor system provided with an assembly according to one of the preceding clauses.   30. A lithographic apparatus, comprising:
   a mask support constructed to support a patterning device,   a first positioner configured to position the mask support with respect to the first positioner,   a substrate support constructed to hold a substrate,   a second positioner configured to position the substrate support with respect to the second positioner, and   a projection system configured to project a pattern imparted to a radiation beam by the patterning device onto a target position on the substrate;   
wherein one or more of the following items:
   the mask support,   the first positioner,   the substrate support, and   the second positioner,   
are provided with an assembly according to one of the clauses 1-28.   

     GENERAL STATEMENTS 
     In accordance with the present invention, ‘cryogenic cooling’ or ‘cooling the coil layer to a cryogenic temperature’ refers to a process of cooling the coil layer to such a temperature that the coils exhibit a superconductive behavior and keeping the coils at such a temperature. As such, when cooled to such a temperature, the coils may be supplied with an electrical current, substantially without generating Ohmic losses. As will be appreciated by the skilled person, the required temperature or cooling may depend on the material or composition of the applied coils and/or the pressure conditions prevailing. 
     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. 
     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. 
     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. 
     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. 
     While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.