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    公开号:NL2009036A
    申请号:NL2009036
    申请日:2012-06-20
    公开日:2013-01-22
    发明作者:Thomas Warmerdam；Marcel Baggen；Peter Hempenius；Youssef Vos
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD FIELD
    [0001] The present invention relates to a lithographic apparatus, a positioning device and a method for manufacturing a device.
    BACKGROUND
    [0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In order to scan the substrate synchronously with the patterning device, the substrate can e.g. be mounted to a support such as a substrate table or a chuck which can be displaced by means of a positioning device. During such scanning, a position measurement system such as an interferometer or encoder measurement system is operational to accurately monitor the position of the support. In general, such a positioning device comprises a short stroke actuator assembly for accurate position of the substrate over a comparatively short stroke and a long stroke motor assembly for positioning the substrate over a comparatively long range or stroke. In such an arrangement, the short stroke actuator assembly, e.g. comprising a plurality of actuators for positioning the substrate table in 6 degrees of freedom (DOF) can e.g. be mounted to the long stroke motor assembly. The long stroke motor assembly can e.g. comprise one or more linear motors but may also comprise a so-called planar motor for 2-dimensional positioning of the substrate table.
    [0003] In a lithographic apparatus, particular care has to be taken to ensure that, in case of an error or failure of a control system or measurement system, no components are damaged due to this error or failure. In particular, due to the considerable forces applied by a positioning device, a loss of control of such a positioning device or a component of the positioning device, may, in case such device or component would contact another component of the apparatus, cause considerable damage to the apparatus. In case of such a failure, or in general, the occurrence of an emergency situation, it is desirable to ensure that a controlled stop of the long stroke motor of the positioning device can be performed, preferably as fast as possible. In particular when such a long stroke motor assembly comprises an electromagnetic motor such as a planar or a linear motor that applies magnetic forces for vertical positioning of the substrate table, such a controlled stop may be difficult to realize, e.g. when a failure of a position measurement system occurs.
    SUMMARY
    [0004] It is desirable to enable a controlled stop of an electromagnetic motor applied for positioning an object table in a lithographic apparatus in case of an error situation.
    [0005] According to an embodiment of the invention, there is provided a lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; a positioning device for positioning the substrate table and/or the support, the positioning device comprising: an electromagnetic motor arranged to displace the substrate table and/or support mounted to a first member of the electromagnetic motor by, in use, generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; a controller to control the force generated between the first and second member of the electromagnetic motor, the controller comprising an input terminal for receiving an error signal; a sensor to provide a sensor signal to the controller to derive a position of the first member relative to the second member; wherein the controller is configured to, upon receipt of the error signal: - derive a vertical position and vertical velocity of the first member relative to the second member from the sensor signal; - determine a start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity; - control the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; and - control the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    [0006] In another embodiment of the invention, there is provided a positioning device comprising: an electromagnetic motor arranged to displace an object or object table mounted to a first member of the electromagnetic motor by, in use, generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; a controller to control the force generated between the first and second member of the electromagnetic motor, the controller comprising an input terminal for receiving an error signal; a sensor to provide a sensor signal to the controller to derive a position of the first member relative to the second member; wherein the controller is configured to, upon receipt of the error signal: - derive a vertical position and vertical velocity of the first member relative to the second member from the sensor signal; - determine a slarl-lo-brake position of the first member relative to the second member based on the vertical position and vertical velocity; - control the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; - control the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    [0007] In yet another embodiment of the present invention, there is provided a device manufacturing method comprising transferring a pattern from a patterning device onto a substrate, positioning the substrate relative to the patterning device using a positioning device by displacing the substrate and/or patterning device mounted to a first member of an electromagnetic motor of the positioning device by generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; and, in case of an error situation, deriving a vertical position and vertical velocity of the first member relative to the second member from a sensor signal; - determining a start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity; - controlling the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; - controlling the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    BRIEF DESCRIPTION OF THE DRAWINGS
    [0008] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
    [0009] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;
    [0010] Figures 2a-2c depict a first member and second member of a planar electromagnetic motor as can be applied in a lithographic apparatus or positioning device according to an embodiment of the invention.
    [0011] Figure 3 schematically depicts a side view of a linear electromagnetic motor as can be applied in a lithographic apparatus or positioning device according to an embodiment of the invention.
    [0012] Figure 4 schematically shows a simulation of an emergency stop of an electromagnetic motor when embodiments of the invention are not applied.
    [0013] Figure 5 schematically shows a simulation of an emergency stop of an electromagnetic motor when embodiments of the invention are applied.
    DETAILED DESCRIPTION
    [0014] Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes an illumination system (illuminator) 1L configured to condition a radiation beam B (e.g. UV radiation or any other suitable radiation), a patterning device support or support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioning device PM configured to accurately position the patterning device in accordance with certain parameters. The apparatus also includes a substrate table (e.g. a wafer table) WT or "substrate support" constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters. The apparatus further includes 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. including one or more dies) of the substrate W.
    [0015] The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
    [0016] The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”
    [0017] The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
    [0018] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
    [0019] Tn an embodiment, the patterning device may comprises an array (e.g. one- or two-dimensional) of light sources that can be configured or programmed to form a radiation beam have a desired pattern, i.e. a patterned radiation beam. In such arrangement, the light sources can e.g. comprise LEDs or one or more laser sources or the like. Arranging the light sources to form the one- or two-dimensional array may e.g. be established using light guides such as optical fibers.
    [0020] The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, 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”.
    [0021] As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
    [0022] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or "substrate supports" (and/or two or more mask tables or "mask supports"). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.
    [0023] The lithographic apparatus may also 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 and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device (e.g. mask) and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.
    [0024] Referring to Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
    [0025] The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
    [0026] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device (e.g. 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. With the aid of the second positioning device PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure (e.g. mask table) MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioning device PM. Similarly, movement of the substrate table WT or "substrate support" may be realized using a long-stroke module and a short-stroke module, which form part of the second positioning device PW. In the case of a stepper (as opposed to a scanner) the support structure (e.g. mask table) MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device (e.g. mask) MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks PI, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device (e.g. mask) MA, the patterning device alignment marks may be located between the dies.
    [0027] The depicted apparatus could be used in at least one of the following modes: 1. Tn step mode, the support structure (e.g. mask table) MT or "mask support" and the substrate table WT or "substrate support" are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT or "substrate support" is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
    2. In scan mode, the support structure (e.g. mask table) MT or "mask support" and the substrate table WT or "substrate support" are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT or "substrate support" relative to the mask table MT or "mask support" may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
    3. In another mode, the support structure (e.g. mask table) MT or "mask support" is kept essentially stationary holding a programmable patterning device, and the substrate table WT or "substrate support" is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or "substrate support" or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.
    [0028] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
    [0029] In accordance with an embodiment of the present invention, the lithographic apparatus comprises a positioning device such as the positioning device PM or PW as described above for positioning a table or support to which, in use, a substrate or pattering device such as a mask or reticle is mounted.
    [0030] In accordance with the an embodiment of the invention, the positioning device comprises an electromagnetic motor such as a linear motor or a planar motor. In general, such a motor comprises a first and second member co-operating to generate a force acting between the first and second member. As an example of such an electromagnetic motor, Figures 2a and 2b schematically show a top view of a first and second member of a planar electromagnetic motor; the first member 110 comprising 4 coil sets 120, each coil set comprising 3 coils. The second member 150 comprising an two-dimensional arrangement of permanent magnets 160 arranged to form a two-dimensional periodically varying magnetic field (the orientation of the magnets by either the arrows or the indication N and S). In Figure 2c, a top view of a planar motor schematically showing both the first and second member is shown. By providing the appropriate currents to the coil sets, the first member 110 can be arranged to displace relative to the second member 150 in both X, Y and Z-direction. In Figure 2c, the arrows 170 schematically indicate the direction of the horizontal forces that can be generated by the different coil sets as shown.
    [0031] The planar motor as schematically shown may e.g. be applied for positioning a substrate table in a lithographic apparatus according to an embodiment of the invention. In such arrangement, the substrate table can e.g. be mounted to the first member 110 of the planar motor, e.g. via a short stroke module for accurate positioning of the substrate table.
    [0032] With respect to the planar motor as depicted in Figures 2a-2c, it is worth noting that in an alternative arrangement, the first member 110 can be provided with a two-dimensional array of permanent magnets while the second member is arranged with a plurality of coil sets that can be supplied with the appropriate currents to generate the required forces for positioning the first member relative to the second member in order to e.g. position an object table such as a substrate table.
    [0033] In accordance with an embodiment of the present invention, the positioning device further comprises a control unit or controller to control the force as generated between the first and second member of the electromagnetic motor. As mentioned, by providing the appropriate currents to the different coils of the first member 110, a force can be generated acting between the first and second member. As will be acknowledged by the skilled person, such currents (e.g. provide by a two- or three phase current system) may generate a force in a given direction (e.g. the X-direction) which can be maintained substantially constant when the first member is displaced in said given direction by a proper commutation of the supplied currents. As such, using the appropriate commutation or commutation angle, the first member can be arranged to displace relative to the second member in the XY-plane (as indicated in Figures 2a-c) while at the same time, a substantially constant vertical force (operating in the Z-direction being perpendicular to the XY-plane) can be generated which causes the first member to levitate above the second member. Note that, in order to generate such a constant force, various arrangements of coils forming a coil set such as coil sets 120 are feasible, taking the magnetic pitch τ of the magnetic field distribution of the second member 150 into account. As the electromagnetic motor as described can also generate forces in the Z-direction, the first and second member can thus displace relative to each other in a contactless manner, without the requirement of e.g. air bearings or other types of bearing. Note that in a similar manner, a linear motor can be made comprising a first member having a plurality of coils and a second member having a linear array of permanent magnets arranged to generate a periodically varying magnetic field. In Figure 3, a side view of such a linear electromagnetic motor is schematically shown, showing the first member 310 and the second member 350, the first member comprising two coil sets 320 (each comprising 3 coils), the second member comprising an array of permanent magnets 150 of alternating polarity. By appropriate commutation, forces can be generated enabling the first member to displace relative to the second member in both the Z-direction and the Y-direction as indicated in Figure 3.
    [0034] As will be understood by the skilled person, in order to provide the appropriate currents for obtaining the desired forces, the relative position of the first and second member, in particular the position of the coils relative to the magnetic field as generated needs to be known.
    [0035] During normal operation of the lithographic apparatus, such position can e.g. be derived from a position measurement system such as the interferometer system IF as depicted in Figure 1.
    [0036] In case of an emergency or error situation, it has been found by the inventors that the planar or linear motors as described may be difficult to maintain under control, e.g. when the feedback of a position measurement system such as the IF system becomes unavailable.
    [0037] Assuming e.g. that the electromagnetic motor is operating at a comparatively high horizontal velocity which needs to be stopped (due to an error situation) and the position measurement system that is used during normal operation (e.g. an interferometer or encoder based measurement system) cannot relied on. In such a situation, it is difficult to reduce the horizontal velocity by generating a horizontal braking force without proper feedback of the relative position. As will he understood by the skilled person, if, in an attempt to generate such a horizontal braking force, an error is made in the commutation angle of the supplied currents, such an error may have an important effect on the vertical forces that are generated. Such vertical forces may result in or lead to damage of e.g. a short stroke actuator assembly mounted to the first member of the motor.
    [0038] Further, as already indicated, the closed loop control that is available during normal operation (providing an accurate position feedback) may be unavailable during an error situation and can, as such not be relied upon.
    [0039] In this respect, it can be noted that, in accordance with an embodiment of the present invention, an error situation may encompass a variety of situations including the situations: a power failure of one or more components, e.g. the position measurement system; an out-of-range situation whereby e.g. the long stroke positioning device is no longer within its nominal working range.
    [0040] As such, it has been devised that the preferred way to ensure that an electromagnetic motor as described is brought to a controlled stop is to bring the first and second member of the motor vertically together in a controlled manner.
    [0041] In order to realize this, the positioning device according to an embodiment of the invention which can be applied in the lithographic apparatus according to an embodiment of the invention comprises a sensor (which can comprise one or more separate sensors) that can provide a sensor signal to the control unit from which a relative position of the first and second member can be derived. Such a signal can e.g. be provided at a dedicated terminal of the control unit. In Figure 3, two of such sensors 380 as schematically shown, mounted to the first member 310, and a control unit 400 for controlling the force generated by the coil sets.
    [0042] As a first example, one or more accelerometers can be applied to provide such a signal. When e.g. starting from a known position, an accelerometer signal (of an accelerometer mounted to the first member) is monitored and integrated twice, an estimate of the relative position between the first and second member can be obtained. This principle can be applied to generate a position estimate in the (horizontal) XY-plane but also in the Z-direction.
    [0043] As a second example, one or more Hall-sensors or other types of magnetic field sensors could be applied to provide a signal from which a relative position can be derived.
    [0044] As a third example, Eddy current sensors can be applied to provide a signal from which a relative position can be derived.
    [0045] Further, other types of sensors such as capacitive sensors could be used to provide a signal useful to provide an indication of the distance in vertical direction between the first and second member.
    [0046] Tn accordance with an embodiment of the invention, the sensor can comprise one or more sensors which may e.g. be of a different type.
    [0047] In accordance with an embodiment of the present invention, the signal as provided by the sensor is used by the control unit to derive a vertical position and vertical velocity of the first member relative to the second member. Based on this information, the control unit is constructed and arranged to control the electromagnetic motor to generate an attractive force between the first and second member of the motor.
    [0048] In an embodiment, the applied vertical attractive force is predetermined and can e.g. be set equal to the maximum allowable or available force, which is e.g. limited by the currents that can be supplied to the electromagnetic motor.
    [0049] In accordance with an embodiment of the invention, this vertical attractive force is applied until a start-to-brake position is obtained. In accordance with an embodiment of the invention, this start-to-brake position can be characterized as a particular vertical position of the first member relative to the second member; i.e. denoting a particular vertical distance between the first and second member. As will be explained in more detail below, this start-to-brake position is determined as the position at which the control unit should switch from operating the motor with a vertical attractive force to operating the motor with a vertical repelling force, whereby the start-to-brake position is determined such that, when the vertical repelling force is applied from the brake position onwards, the first and second member contact each other with a predetermined comparatively low velocity. It will be acknowledged by the skilled person that, for a given available vertical repelling (or braking) force, the position at which the braking (repelling) should start, will depend on the actual vertical velocity of the first member relative to the second member. As such, the control unit of the positioning device is arranged to determining the start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity derived from the sensor signal.
    [0050] As mentioned, once the start-to-brake position is reached, the control unit is arranged to control the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    [0051] Tn an embodiment, the vertical attractive and repelling forces have fixed amplitudes and correspond to the maximum force that can be generated by the electromagnetic motor. Applying the maximum available force to both attract and repel the members of the electromagnetic motor results in a fast but controlled contacting of the first and second member. Once the members make contact, horizontal frictional force can provide a braking force between the first and second member such that the first member can e.g. be brought to a halt.
    [0052] In an embodiment, the available force (which can be generated by the motor) is used to both generate a vertical force (for bringing the first and second member together) and a horizontal force for decelerating the motor.
    [0053] As such, the positioning device as proposed provides an effective way of bringing a support or table to a controlled stop without relying on e.g. an accurate position measurement system as e.g. applied in a lithographic apparatus for position control of an object such as a substrate or a patterning device.
    [0054] By providing a controlled stop resulting in comparatively low landing velocity, any bouncing effects of the first relative to the second member can be mitigated.
    [0055] In an embodiment, the control unit is further arranged to control the electromagnetic motor to generate a vertical attractive force between the first and second member once the first member has contacted the second member.
    [0056] By doing so, an improved horizontal friction force can be obtained once the first member contacts the second member.
    [0057] In an embodiment, the sensor is mounted to the first member of the electromagnetic motor.
    [0058] In an embodiment, the electromagnetic motor is provided with a plurality of sensors providing feedback on different locations of the motor, e.g. the first member. Referring to Figure 2a, each comer of the first member 110 can e.g. be provided with a sensor that provides a signal to the control unit controlling the motor.
    [0059] In an embodiment, (as the embodiment shown in Figure 2a), the electromagnetic motor can comprise a plurality of force-generating units, also referred to as forcers. In the embodiment shown in Figure 2a, each set of three coils can be considered a forcer that can generate a force having a component in both the vertical and horizontal direction.
    Similarly, each coil set 320 of the linear electromagnetic motor as shown in Figure 3 can be considered a forcer of which the vertical and/or horizontal force can be adjusted by applying the appropriate set of currents to the coils.
    [0060] As such, in an embodiment whereby the electromagnetic motor comprises a plurality of forcers, each forcer can be controlled individually, e.g. based on a plurality of sensor signals from a respective plurality of sensors.
    [0061] As an example, referring to Figure 2c, the first member 110 of the planar motor as shown can be provided with 4 sensors arranged near the 4 corners of the first member, whereby the control unit controls each coil set 120 of the first member using a sensor signal of the sensor nearest to the forcer. Furthermore, to be more precise, a measurement system can be built of the available sensors and from the measurement system output, the height of each corner can be calculated. In such arrangement, positional information about the position of the 4 comers of the first member can be derived from the signals of the 4 sensors when the positions of the sensors relative to each other and/or relative to the comers are known. Alternatively or additionally, the sensors are arranged near other positions of extremities such as an edge of the first member.
    [0062] As such, in an embodiment, each forcer can be controlled individually to generate a particular vertical attractive force followed by a particular vertical repelling force. In such embodiment, the applicable vertical forces can be determined based on the weight distribution of the first member.
    [0063] In an embodiment of the present invention, the start-to-brake position (Zbrake) is calculated as follows:
    (1) wherein:
    Vz = vertical velocity;
    Viand = desired velocity when the first and second member make contact, also referred to as landing velocity; a rep = available deceleration level; i.e. representative of the available repelling force.
    [0064] As such, for any vertical velocity Vz and a known available deceleration and desired landing velocity, the control unit can determine Zbrake and assess, based on the vertical position and velocity of the first member relative to the second member (derivable from the sensor signal), whether the start-to-brake position has already been reached or not.
    [0065] In case the electromagnet motor comprises a plurality of forces (as e.g. depicted in Figure 2c) and is thus comparatively large, it may be preferred to apply a higher braking (or repelling force) or to start braking earlier than indicated by equation (1). This may result in a more robust operation of the system; in case of a motor as e.g. depicted in Figure 2c, it may occur that the first member of the motor contacts the second member in a tilted position, e.g. one comer of the first member touching the second member. In such a situation, this contacting may result in an acceleration of one or more of the other corners towards the second member. By applying an increased braking force or starting to brake somewhat earlier, such an acceleration of the one or more other comers can be counteracted.
    [0066] As will be acknowledged by the skilled person, the control strategy as proposed is a highly robust control principle (similar to a bang-bang controller) which is substantially independent of e.g. sample time and if, for some reasons, some samples are missed, the stability of the controller is not affected.
    [0067] The proposed control unit thus provides a closed loop control in the Z-direction which is less demanding with respect to processor frequency, compared to closed loop controllers required for accurate positioning of e.g. a substrate or patterning device. As a consequence, the control unit or controller as proposed can be implemented
    [0068] In Figures 4 and 5, the effects of the application of the controlled stop of the electromagnetic motor are schematically shown.
    [0069] Figure 4 schematically shows in the upper graph the vertical position d of ihe first member relative to the second member as a function of time t, without application of the vertical attractive and repelling forces as proposed in an embodiment of the invention. The lower graph schematically shows a corresponding typical vertical force F exerted on the first member as a function of time t. In the graph, the dotted line schematically depicts typical forces that are exerted on a short stroke assembly that is e.g. mounted to the first member.
    [0070] In Figure 5, the same characteristics are shown (i.e. the relative position d of the first and second member and the vertical force F on the first member an on a short stroke assembly (dotted line)) when the control strategy as provided by the invention is applied. As can be seen when comparing both Figures, although the first member touches the second member later when the invention is applied (situation as depicted in Figure 5), the motor is brought to a halt much sooner; As can be noted, the first member hardly bounces up when the invention is applied, thus strongly reducing the risk of damaging e.g. short stroke actuator assembly, or a table that is mounted to the first member. Further, the vertical forces acting on the first member are substantially higher, increasing the risk of damage to either the first or second member, when the invention is not applied.
    [0071] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as 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. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
    [0072] 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 may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
    [0073] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.
    [0074] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
    [0075] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
    [0076] 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 clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A lithographic apparatus comprising: a patterning device support constructed to support a patterning device, the patterning device being configured to impart a radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; a positioning device configured to position one of the supports, the positioning device comprising: an electromagnetic motor arranged to displace said one support mounted to a first member of the electromagnetic motor by, in use, generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; a controller configured to control the force generated between the first and second member of the electromagnetic motor, said controller comprising an input terminal to receive an error signal; a sensor configured to provide a sensor signal to the controller to derive a position of the first member relative to the second member; wherein the controller is configured to, upon receipt of the error signal: derive a vertical position and vertical velocity of the first member relative to the second member from the sensor signal; determine a start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity; control the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; control the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    2. The lithographic apparatus according to clause 1, wherein the sensor is mounted to the first member.
    3. The lithographic apparatus according to clause 1 or 2, wherein the sensor comprises an accelerometer, Hall sensor or an eddy current sensor.
    4. The lithographic apparatus according to any preceding clause, wherein the electromagnetic motor comprises a planar motor or a linear motor.
    5. The lithographic apparatus according to any preceding clause, wherein the first member is provided with a plurality of coils arranged to, in use, co-operate with a magnetic field distribution of a plurality of permanent magnets of the second member to separate the first member from the second member by electromagnetic forces.
    6. The lithographic apparatus according to any preceding clause, wherein the start-to-brake position (Zbrake) is determined as:
    wherein:
    Vz = vertical velocity;
    Viand = desired landing velocity; arep = available deceleration.
    7. The lithographic apparatus according to any preceding clause, wherein the electromagnetic motor comprises a plurality of forcers that are individually controllable by the controller to generate a plurality of force components of the force.
    8. The lithographic apparatus according to clause 7, wherein the sensor signal comprises a plurality of signals to derive a plurality of positions of the first member relative to the second member.
    9. The lithographic apparatus according to clause 8, wherein the plurality of positions substantially corresponds to positions of extremities such as comers of the first member.
    10. The lithographic apparatus according to any of the clauses 7 to 9, wherein the plurality of force components are based on a weight distribution of the first member.
    11. The lithographic apparatus according to any preceding clause, wherein the controller is configured to control the electromagnetic motor to generate a further vertical attractive force between the first and second member when the first member has contacted the second member.
    12. The lithographic apparatus according to any preceding clause, wherein the controller is configured to, during use, control the electromagnetic motor to maintain a vertical distance between the first and second member by electromagnetic forces.
    13. The lithographic apparatus according to any preceding clause, wherein the force, in use, comprises both a vertical and a horizontal component.
    14. A positioning device comprising: an electromagnetic motor arranged to displace an object or object table mounted to a first member of the electromagnetic motor by, in use, generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; a controller configured to control the force generated between the first and second member of the electromagnetic motor, said controller comprising an input terminal to receive an error signal; a sensor configured to provide a sensor signal to the controller to derive a position of the first member relative to the second member; wherein the controller is configured to, upon receipt of the error signal: derive a vertical position and vertical velocity of the first member relative to the second member from the sensor signal; determine a start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity; control the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; control the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    15. A device manufacturing method comprising: transferring a pattern from a patterning device onto a substrate; positioning the substrate relative to the patterning device using a positioning device by displacing the substrate and/or patterning device mounted to a first member of an electromagnetic motor of the positioning device by generating a force between the first member of the electromagnetic motor and a second member of the electromagnetic motor; and, in case of an error situation, deriving a vertical position and vertical velocity of the first member relative to the second member from a sensor signal; determining a start-to-brake position of the first member relative to the second member based on the vertical position and vertical velocity; controlling the electromagnetic motor to generate a vertical attractive force between the first and second member until a vertical distance between the first and second member substantially corresponds to the start-to-brake position; controlling the electromagnetic motor to generate a vertical repelling force between the first and second member until the first member contacts the second member.
    权利要求:
    Claims (1)
    [1]
    A lithography device comprising: an illumination device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.
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    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    法律状态:
    2013-11-20| WDAP| Patent application withdrawn|Effective date: 20130813 |
    优先权:
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    US201161509881P| true| 2011-07-20|2011-07-20|
    US201161509881|2011-07-20|
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