Anti-vibration apparatus, exposure apparatus using the same, device manufacturing method, and anti-vibration method

An anti-vibration apparatus for actively damping vibrations of an object by generating control forces for reducing the vibrations includes a first actuator for generating a first control force, and a second actuator which generates a second control force and is driven on a driving principle different from that for the first actuator. The first actuator generates forces in the vertical and horizontal directions. The second actuator generates a force in at least one of the vertical and horizontal directions.

BACKGROUND OF THE INVENTION
 Field of the Invention
 The present invention relates to an anti-vibration apparatus on which an
 object to be vibration-damped and isolated from vibrations is mounted and,
 more particularly, to an active anti-vibration apparatus used in precision
 equipment such as a semiconductor exposure apparatus having a moving
 mechanism, e.g., an X-Y stage. The present invention also relates to an
 exposure apparatus having this anti-vibration apparatus and a device
 manufacturing method using the exposure apparatus. In addition, the
 present invention relates to anti-vibration method of mounting an object
 to be vibration-damped and isolated from vibrations.
 With improvements in the preciseness of precision equipment such as an
 electron microscope and a semiconductor exposure apparatus, enhancement of
 performance of precision anti-vibration apparatuses that mount them has
 been demanded. In a semiconductor exposure apparatus, in particular, an
 anti-vibration table from which external vibrations from a pedestal,
 (apparatus installation pedestal) such as a floor which the apparatus is
 mounted, are removed as much as possible, is required to realize proper
 and quick exposure. This is because vibrations that adversely affect
 exposure must be prevented from being produced in the exposure stage.
 In a semiconductor exposure apparatus characterized by intermittent
 motions, such as step & repeat motions, the repetitive step operation of
 the X-Y stage induces vibrations of the anti-vibration table. This is
 because a driving reaction force of the X-Y stage and the load movement of
 the X-Y stage induce vibrations of the anti-vibration table. The
 anti-vibration table is, therefore, required to have an anti-vibration
 function against external vibrations from a pedestal such as a floor on
 which the apparatus is installed and a vibration control function against
 vibrations caused by the motions of the equipment mounted on the
 anti-vibration table.
 Some semiconductor exposure apparatuses use the scan exposure scheme
 instead of the step & repeat scheme. In such an apparatus as well,
 externally transmitted vibrations such as vibrations from the apparatus
 installation pedestal must be removed as much as possible, and vibrations
 of the anti-vibration table which are induced by the scanning operation of
 the exposure stage must be instantaneously damped. In a scan exposure
 apparatus, in particular, since exposure is performed while the exposure
 stage is performing a scanning operation, both the anti-vibration function
 against external vibrations and the vibration control function against
 vibrations caused by the motions of the equipment mounted on the
 anti-vibration table must meet strict requirements. An anti-vibration
 apparatus with higher performance becomes indispensable.
 To meet such requirements, an active anti-vibration apparatus has recently
 been put into practice, which detects vibrations of an anti-vibration
 table through a sensor, and compensates for the output signal from the
 sensor to feed back the resultant signal to an actuator for applying a
 control force to the anti-vibration table, thereby actively controlling
 the vibrations of the anti-vibration table. An active anti-vibration
 apparatus can realize an anti-vibration apparatus having the
 anti-vibration function and the vibration control function with a good
 balance, which is difficult for a passive anti-vibration apparatus
 comprised of springs, dampers, and the like to realize.
 As an actuator for applying a control force to an anti-vibration table, a
 conventional active anti-vibration apparatus generally uses a pneumatic
 actuator for actively controlling a thrust to be generated by adjusting
 the internal pressure of a pneumatic spring.
 In an anti-vibration apparatus that mounts precision equipment, to maximize
 the anti-vibration function by minimizing the natural frequency of a
 vibration system constituted by an anti-vibration table and a support
 mechanism for damping/supporting the anti-vibration table, it is effective
 to increase the weight of the anti-vibration table and use pneumatic
 springs, having a small spring constant, for the support mechanism of the
 anti-vibration table. In addition, the pneumatic springs can easily
 generate large thrusts by increasing their pressure-receiving areas, and
 hence, can be suitably used as a support mechanism for supporting a heavy
 anti-vibration table. If, therefore, a pneumatic actuator is used as an
 actuator for applying a control force to an anti-vibration table, an
 anti-vibration apparatus having a relatively simple structure can be
 realized because the actuator can also serve as a damper support mechanism
 for the anti-vibration table.
 When, however, a device having a driving means such as an X-Y stage is
 mounted on an anti-vibration table, as in a semiconductor exposure
 apparatus, the required vibration suppressing effect cannot always be
 obtained by an active anti-vibration apparatus using a pneumatic actuator.
 In general, an X-Y stage has a mechanism for driving a ball screw by using
 an electromagnetic motor or a structure of linearly driving the stage by
 using an electromagnetic linear motor or the like. That is, the X-Y stage
 is driven by using an electromagnetic actuator exhibiting fast-response
 characteristics with respect to a driving force command signal. In
 contrast to this, the response of the pneumatic actuator to a driving
 force command signal is slower than that of the electromagnetic actuator.
 In general, the response frequency of the pneumatic actuator is lower than
 that of the electromagnetic actuator by 100 times or more. For this
 reason, the active anti-vibration apparatus using the pneumatic actuator
 cannot generate a control force corresponding to a driving reaction force
 of the X-Y stage driven by the electromagnetic actuator at a satisfactory
 response speed, thus failing to obtain a sufficient vibration suppressing
 effect.
 In order to solve such a problem, an electromagnetic actuator may be used
 as an actuator for applying a control force to an anti-vibration table.
 For example, as such an apparatus, an anti-vibration apparatus designed to
 magnetically float the anti-vibration table by using the attraction force
 of an electromagnet is available. As described above, however, the
 anti-vibration table that mounts precision equipment is very heavy, and
 hence, very high energy must be applied to the apparatus to support/drive
 the anti-vibration table with an electromagnetic force. In the
 electromagnetic actuator, in particular, heat is generated by coil
 windings used to generate an electromagnetic force. If, therefore, the
 actuator is driven by applying high energy, a large quantity of heat is
 generated. But, precision equipment including a semiconductor exposure
 apparatus and the like is greatly influenced by changes in temperature;
 the apparatus performance is seriously affected even by a 1.degree. C.
 rise in apparatus temperature. Therefore, it is unfavorable if the
 electromagnetic actuator produces a large amount of heat.
 As higher preciseness and throughput are required for semiconductor
 exposure apparatuses, there are great demands for an active anti-vibration
 apparatus that can support a heavy anti-vibration table and equipment
 mounted thereon and generate a control force in quick response to a
 driving reaction force of a device such as an X-Y stage which is driven on
 the anti-vibration table at high speed. Such requirements have become
 stricter in the field of next-generation semiconductor exposure
 apparatuses and the like, in which it is expected that a driving reaction
 force of an X-Y stage will increase with an increase in driving speed.
 When vibrations produced by such a driving reaction force are to be damped
 and controlled by using an anti-vibration apparatus, damping and vibration
 control operation must be performed not only in the vertical direction but
 also in the horizontal direction. In a semiconductor exposure apparatus or
 the like, importance is often attached to the integration of an
 anti-vibration apparatus as a unit. In addition, it is difficult for a
 conventional anti-vibration apparatus using an air cylinder to perform
 damping and vibration control in both the vertical and horizontal
 directions. To realize this, the apparatus inevitably increases in
 complexity. Demands have, therefore, arisen for an anti-vibration
 apparatus that is made up of more compact components and appropriately
 integrated with an exposure apparatus with the components being
 efficiently arranged.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide an active
 anti-vibration apparatus which has a compact structure, satisfies the
 above requirements, maximizes the characteristics of a pneumatic actuator
 capable of steadily generating a large thrust and an electromagnetic
 actuator having fast-response characteristics, and minimizes the
 influences of heat on the device such as a semiconductor exposure
 apparatus mounted on an anti-vibration table, an exposure apparatus using
 this active anti-vibration apparatus, a device manufacturing method using
 the exposure apparatus, and an anti-vibration method.
 In order to achieve the above object, according to the present invention,
 there is provided an anti-vibration apparatus for actively damping
 vibrations of an object by generating control forces to reduce the
 vibrations, comprising a first actuator for generating a first control
 force, and a second actuator for generating a second control force, the
 second actuator using a driving principle different from that of the first
 actuator, wherein the first actuator generates forces in vertical and
 horizontal directions, and the second actuator generates a force at least
 in one of the vertical and horizontal directions.
 According to this anti-vibration apparatus, vibrations of an object can be
 actively reduced by generating the forces in the vertical and horizontal
 directions, and the respective components are made more compact and
 efficiently arranged to realize a compact anti-vibration apparatus.
 There is provided an exposure apparatus comprising anti-vibration means
 using the above anti-vibration apparatus.
 Since vibrations of the components of the exposure apparatus are accurately
 damped, the exposure apparatus can perform high-speed, high-precision
 exposure.
 There is provided a method of manufacturing a device by using the above
 exposure apparatus, comprising the steps of providing the above, and
 transferring a pattern formed on a reticle onto a wafer.
 A device can be manufactured at high speed with high precision by this
 device manufacturing method.
 There is provided an anti-vibration method comprising the steps of
 detecting a displacement or vibration of a damped/supported object,
 extracting signals representing motion modes of translation and rotation
 from the detection values, performing a compensation operation on the
 basis of the signals, and controlling, based on the compensation
 operation, at least one of a first actuator for generating forces in
 vertical and horizontal directions and a second actuator which generates a
 force in at least one of the vertical and horizontal directions and is
 driven on a driving principle different from a driving principle of the
 first actuator.
 According to this anti-vibration method, vibrations of a damped/supported
 object can be accurately damped in the vertical and horizontal directions.
 There is provided an anti-vibration method comprising the steps of
 performing a feedforward compensation operation on the basis of the state
 of the device mounted on an anti-vibration apparatus or a signal from the
 device and controlling, based on the compensation operation, at least one
 of a first actuator for generating forces in vertical and horizontal
 directions and a second actuator which generates a force in at least one
 of the vertical and horizontal directions and is driven by a driving
 principle different from a driving principle of the first actuator.
 According to this anti-vibration method, vibrations of a device mounted on
 the anti-vibration apparatus can be accurately damped in the vertical and
 horizontal directions by feedforward compensation.
 According to a preferred aspect of the present invention, the first
 actuator of the anti-vibration apparatus has one of a pneumatic actuator
 and an electromagnetic linear motor, and the second actuator has the other
 of the pneumatic actuator and the electromagnetic linear motor.
 According to this anti-vibration apparatus, a large thrust can steadily be
 generated by using the pneumatic actuator with almost no heat generated.
 In addition, vibrations can be damped at a high response speed by using
 the electromagnetic linear motor in combination with the pneumatic
 actuator.
 According to another preferred aspect of the present invention, the first
 actuator of the anti-vibration apparatus includes two actuators for
 generating forces in the vertical and horizontal directions.
 According to still another preferred aspect of the present invention, the
 second actuator of the anti-vibration apparatus includes two actuators for
 generating forces in the vertical and horizontal directions.
 According to still another preferred aspect of the present invention, the
 actuator of the anti-vibration apparatus which generates the force in the
 horizontal direction has the opposing pneumatic actuator.
 According to this anti-vibration apparatus, a large thrust can be generated
 in the horizontal direction and a displacement can be provided by using
 the opposing pneumatic actuator.
 According to still another preferred aspect of the present invention, the
 actuator of the anti-vibration apparatus which generates a force in the
 horizontal direction has the pneumatic actuator and a pre-pressurizing
 mechanism.
 According to this anti-vibration apparatus, by using the pneumatic actuator
 and the pre-pressuring mechanism, a large thrust and displacement can be
 provided in the horizontal direction, and control of an air pressure and
 piping can be facilitated.
 According to still another preferred aspect of the present invention, in
 the anti-vibration apparatus, the axis of action of the first actuator for
 generating the force in the vertical direction substantially coincides
 with the axis of action of the second actuator for generating the force in
 the vertical direction.
 According to still another preferred aspect of the present invention, in
 the anti-vibration apparatus, the axis of action of the first actuator for
 generating the force in the horizontal direction substantially coincides
 with the axis of action of the second actuator for generating the force in
 the horizontal direction.
 According to still another preferred aspect of the present invention, in
 the anti-vibration apparatus, fixation parts of the first and also the
 second actuators are established as a unit, and mobile parts of the first
 and also the second actuators are established as a unit.
 According to still another preferred aspect of the present invention, in
 the anti-vibration apparatus, a fixation part of the first actuator for
 generating a force in a vertical direction and a fixation part of the
 first actuator for generating a force in a horizontal direction are
 established as a unit, and a mobile part of the first actuator for
 generating a force in a vertical direction and a mobile part of the first
 actuator for generating a force in a horizontal direction are established
 as a unit.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus comprises at least one of passive elastic support
 means and passive vibration damping means.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus further comprises displacement detection means
 for detecting a displacement of a control target.
 According to this anti-vibration apparatus, a displacement can be detected
 by the displacement detection means.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus comprises vibration detection means for detecting
 vibrations of a control target.
 According to this anti-vibration apparatus, vibrations can be detected by
 the vibration detection means.
 According to still another preferred aspect of the present invention, the
 vibration detection means of the anti-vibration apparatus is an
 acceleration sensor.
 According to still another preferred aspect of the present invention, the
 vibration detection means of the anti-vibration apparatus is a velocity
 sensor.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus drives the first or second actuator on the basis
 of at least one of output signals from the displacement detection means
 and the vibration detection means.
 According to this anti-vibration apparatus, a displacement or vibration is
 detected, and forces are generated by the first and second actuators on
 the basis of the detection value, thereby accurately damping vibrations in
 the vertical and horizontal directions with a compact structure.
 According to still another preferred aspect of the present invention, the
 output signal from the displacement detection means of the anti-vibration
 apparatus is compensated for and fed back to the pneumatic actuator.
 According to still another preferred aspect, the output signal from the
 vibration detection means of the anti-vibration apparatus is compensated
 for and fed back to the electromagnetic linear motor.
 According to still another preferred aspect of the present invention, the
 pneumatic actuator of the anti-vibration apparatus has a dead zone in a
 direction perpendicular to the direction in which the force is generated.
 According to this anti-vibration apparatus, since each pneumatic actuator
 has a backlash in a direction perpendicular to the direction in which a
 force is generated, the pneumatic actuators in the vertical and horizontal
 directions do not interfere with each other, and vibrations in the two
 directions can be damped.
 According to still another preferred aspect of the present invention, the
 pneumatic actuator of the anti-vibration apparatus has a bellows
 structure.
 According to this anti-vibration apparatus, since each pneumatic actuator
 is formed by using a bellows structure, a compact anti-vibration apparatus
 with a high degree of integration can be provided.
 According to still another aspect of the present invention, the pneumatic
 actuator of the anti-vibration apparatus has a pressure control valve for
 adjusting the internal pressure of the pneumatic actuator or a flow rate
 valve for adjusting the flow rate of air supplied/exhausted.
 According to still another preferred aspect of the present invention, the
 pneumatic actuator of the anti-vibration apparatus comprises a pressure
 sensor for detecting the internal pressure of the pneumatic actuator, and
 has a pressure control loop for actuating at least one of the pressure
 control valve and the flow rate control valve on the basis of a
 compensation signal obtained from the pressure compensation means.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motor of the anti-vibration apparatus is a moving
 magnet type linear motor.
 According to this anti-vibration apparatus, the influences of heat on an
 object whose vibrations must be damped can be reduced, and wiring of the
 coil winding can be facilitated.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motor of the anti-vibration apparatus has a
 structure in which a coil is placed in a magnetic field between a
 plurality of opposing magnets.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motor of the anti-vibration apparatus is a
 single-phase linear motor having one coil.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motor of the anti-vibration apparatus is a
 polyphase linear motor having a plurality of coils.
 According to still another preferred aspect of the present invention, each
 of the plurality of coils of the anti-vibration apparatus is energized in
 a direction opposite to a direction in which a current flows in a
 corresponding adjacent coil.
 According to this anti-vibration apparatus, undesired thrust components
 produced in each electromagnetic linear motor can be easily reduced, and a
 high-precision anti-vibration apparatus can be provided by using
 high-precision, low-cost electromagnetic linear motors.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motor of the anti-vibration apparatus comprises an
 interpole magnet.
 According to this anti-vibration apparatus, the magnetic flux generated by
 each electromagnetic linear motor can be made uniform and strong, and the
 thrust generated by each electromagnetic linear motor can be increased,
 thereby realizing a high-precision anti-vibration apparatus.
 According to still another preferred aspect of the present invention, each
 of the first and second actuators of the anti-vibration apparatus
 comprises a plurality of actuators.
 According to this anti-vibration apparatus, vibrations in motion modes of
 translation and rotation can be damped and controlled by arranging a
 plurality of first and second actuators.
 According to still another preferred aspect of the present invention, the
 plurality of electromagnetic linear motors or coils of the electromagnetic
 linear motors arranged in the anti-vibration apparatus are formed into
 several groups, and a plurality of electromagnetic linear motors or coils
 of the electromagnetic linear motors which are included in the same group
 are driven by the same driving signal.
 According to still another preferred aspect of the present invention, the
 electromagnetic linear motors or coils of the electromagnetic linear
 motors of the anti-vibration apparatus which are driven by the same
 driving signal are electrically connected in series or parallel.
 According to this anti-activation apparatus, signals and wiring of the
 control system of the anti-vibration apparatus can be simplified, and a
 reduction in cost can be achieved.
 According to still another preferred aspect of the present invention, in
 the anti-vibration apparatus, signals representing motion modes of
 translation and rotation are extracted from adisplacement target value and
 output signals from the plurality of displacement detection means, and the
 extracted signals are compensated for to drive at least one of sets of the
 first actuators and the second actuators.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus extracts signals representing motion modes of
 translation and rotation from output signals from the plurality of
 vibration detection means, and compensates for the extracted signals to
 drive at least one of sets of the first actuators and the second
 actuators.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus further comprises first feedforward compensation
 operation means for performing a compensation operation on the basis of a
 state of a device mounted on the anti-vibration apparatus or a signal from
 the device, and drives the first actuator on the basis of a compensated
 signal obtained by a first feedforward compensation operation.
 According to still another preferred aspect of the present invention, the
 anti-vibration apparatus further comprises second feedforward compensation
 operation means for performing a compensation operation on the basis of a
 state of a device mounted on the anti-vibration apparatus or a signal from
 the device, and drives the second actuator on the basis of a compensated
 signal obtained by the second feedforward compensation operation means.
 This anti-vibration apparatus can damp vibrations of a mounted device by
 feedforward compensation.
 According to still another preferred aspect of the present invention, the
 anti-vibration means of the exposure apparatus supports a stage base plate
 and removes vibrations of the stage base plate.
 According to still another preferred aspect of the present invention, the
 anti-vibration means of the exposure apparatus supports a lens barrel base
 plate and removes vibrations of the lens barrel base plate.
 According to still another preferred aspect of the present invention, a
 reticle base plate for supporting a reticle stage of the exposure
 apparatus is coupled to a lens barrel base plate, and the anti-vibration
 means supports the lens barrel base plate and removes vibrations of the
 reticle stage.
 According to still another preferred aspect of the present invention, the
 exposure apparatus is a scan type exposure apparatus.
 According to still another preferred aspect of the present invention, the
 device manufacturing method further comprises the steps of developing a
 portion exposed on the wafer, and cutting a chip formed on the wafer.
 A device can be manufactured at high speed with high precision by this
 device manufacturing method.
 Other features and advantages of the present invention will be apparent
 from the following description taken in conjunction with the accompanying
 drawings, in which like reference characters designate the same or similar
 parts throughout the figures thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Preferred embodiments of the present invention will be described in detail
 in accordance with the accompanying drawings.
 First Embodiment
 In this embodiment, an anti-vibration unit that supports an anti-vibration
 table on which precision equipment such as a semiconductor exposure
 apparatus is mounted, and reduces harmful vibrations that adversely affect
 the mounted equipment, is disclosed.
 FIG. 1 is a schematic view showing an active anti-vibration apparatus
 according to the first embodiment. This embodiment will be described below
 with reference to FIG. 1.
 An anti-vibration table 1 such as a base plate on which precision equipment
 such as a semiconductor exposure apparatus is mounted is supported by an
 anti-vibration unit 50 firmly fastened to the anti-vibration table 1.
 Reference numeral 21 denotes a vertical pneumatic actuator for applying a
 control force to the anti-vibration table 1 in the vertical direction (Z
 direction); 22, a horizontal pneumatic actuator for applying a control
 force to the anti-vibration table 1 in the horizontal direction (X
 direction); 31, a vertical linear motor as an electromagnetic actuator for
 applying a control force to the anti-vibration table 1 in the vertical
 direction; and 32, a horizontal linear motor as an electromagnetic
 actuator for applying a control force to the anti-vibration table 1 in the
 horizontal direction. The anti-vibration unit 50 includes the vertical
 pneumatic actuator 21, the horizontal pneumatic actuator 22, the vertical
 linear motor 31, and the horizontal linear motor 32.
 The anti-vibration unit 50 also has a vertical vibration sensor 26a and a
 horizontal vibration sensor 26b which respectively detect vibration
 signals representing accelerations or velocities of the anti-vibration
 table 1 or anti-vibration unit 50, which is firmly fastened to the
 anti-vibration table 1, in the vertical and horizontal directions.
 The anti-vibration unit 50 also has a vertical displacement sensor 25a and
 a horizontal displacement sensor 25b which respectively detect
 displacement signals to the reference positions.
 The anti-vibration unit 50 may include an elastic support means such as a
 spring mechanism and a passive vibration damping means such as a viscous
 damper. If a pneumatic actuator, to be described later, is used as an
 actuator for applying a control force to the anti-vibration table 1, as in
 the apparatus disclosed in the present invention, the pneumatic actuator
 can also serve as an elastic support means for supporting the
 anti-vibration table 1. In addition, according to this apparatus,
 vibrations of the anti-vibration table 1 can be damped by performing a
 control operation to be described later. The object of the present
 invention can, therefore, be satisfactorily achieved by the anti-vibration
 unit 50 having no passive elastic support means and vibration damping
 means as shown in FIG. 1.
 &lt;Pneumatic Actuator&gt;
 The vertical and horizontal pneumatic actuators 21 and 22 are pneumatic
 actuators for applying control forces to the anti-vibration table 1 and
 will be described next.
 As each of the vertical and horizontal pneumatic actuators 21 and 22, an
 actuator unit made up of a pneumatic spring and a pressure control valve
 for continuously adjusting the internal pressure of the pneumatic spring
 in accordance with an electrical command signal or an actuator unit made
 up of a pneumatic spring and a flow rate control valve for adjusting the
 flow rate of air supplied/exhausted to/from the pneumatic spring can be
 used. As will be described later, these actuators are driven on the basis
 of the displacement of the anti-vibration table 1 with respect to a
 reference position or a compensation signal for vibrations of the
 anti-vibration table 1.
 The vertical pneumatic actuator 21 adjusts a pressure control valve or flow
 rate control valve (not shown) to generate a force in a direction to raise
 the anti-vibration table 1 by increasing the internal pressure of the
 pneumatic spring and a force in a direction to lower the anti-vibration
 table 1 by decreasing the internal pressure of the pneumatic spring. A
 pneumatic actuator of this type using a pneumatic spring cannot generate
 any force except for increasing the internal pressure of the pneumatic
 spring. In the case with the vertical pneumatic actuator 21, however,
 since the weight of the anti-vibration table 1 is applied as a
 pre-pressure to the vertical pneumatic actuator 21, a force in a direction
 to lower the anti-vibration table 1 can be generated by decreasing the
 internal pressure of the pneumatic spring.
 Each pneumatic spring has a rubber bellows structure to ensure a backlash
 (allowable range of movement) in a direction perpendicular to the
 direction in which a force is generated. For example, to prevent the
 horizontal pneumatic actuator from being interfered with with the motions
 of the vertical pneumatic actuator, the bellows structure is designed to
 prevent interference between the respective actuators when vibrations in
 both the vertical and horizontal directions are removed. The structure of
 each pneumatic spring is not limited to the bellows structure as long as
 the actuator can move in a direction perpendicular to the direction in
 which a force is generated. For example, each actuator may have a cylinder
 mechanism having a compensation mechanism in a direction perpendicular to
 the direction in which a force is generated.
 FIG. 1 shows the first example of the arrangement of the horizontal
 pneumatic actuator 22 in this embodiment, which includes two opposing
 pneumatic actuators. In this case, forces in two directions, i.e., the +X
 direction and the opposite direction, the -X direction, indicated by the
 arrows in FIG. 1 can be generated for the anti-vibration table 1 by
 controlling the balance between the forces generated by two pneumatic
 springs 23a and 23b that are arranged opposite to constitute the
 horizontal pneumatic actuators 22. More specifically, the pressure control
 valve or flow rate control valve (not shown) is adjusted to increase the
 internal pressure of the pneumatic spring 23a and decrease the internal
 pressure of the pneumatic spring 23b so as to generate a force in the +X
 direction. In addition, the above valve is adjusted to decrease the
 internal pressure of the pneumatic spring 23a and increase the internal
 pressure of the pneumatic spring 23b so as to generate a force in the -X
 direction.
 Referring to FIG. 1, the horizontal pneumatic actuator 22 in the
 anti-vibration unit 50 corresponds to only one horizontal direction. If,
 however, two or more horizontal pneumatic actuators are used, control
 forces can be applied in a plurality of arbitrary directions.
 FIG. 2 is a conception diagram of the control system for the pneumatic
 actuator.
 The pneumatic actuator preferably has a pressure control loop in which the
 internal pressure of the pneumatic spring is detected by a pressure sensor
 27, the difference signal between a pressure command signal and the output
 signal from the pressure sensor 27 is compensated for by a pressure
 compensation means 48, and a control valve 28 such as a pressure control
 valve or flow rate control valve which is driven on the basis of the
 compensated signal. FIG. 2 schematically shows the control system for the
 vertical pneumatic actuator having the pressure control loop. In this
 case, an input signal (driving command signal) to the pneumatic actuator
 is the pressure command signal shown in FIG. 2.
 &lt;Linear motor&gt;
 Linear motors used as the vertical linear motor 31 and the horizontal
 linear motor 32 will be described next.
 FIGS. 3A to 3C show three views of an electromagnetic linear motor, which
 is the first example of an arrangement of an electromagnetic linear motor
 used as the vertical linear motor 31 or horizontal linear motor 32 in this
 embodiment.
 The electromagnetic linear motor in FIGS. 3A to 3C is a single-phase linear
 motor 33 made up of a coil assembly 33a including one coil winding 33c and
 a magnet assembly 33b including two pairs of opposing permanent magnets
 33d.
 As shown in FIGS. 3A to 3C, the coil assembly 33a is placed in the magnetic
 circuit formed by the magnet assembly 33b so as not to touch the magnet
 assembly 33b. As the coil winding 33c, a copper wire or the like with
 several hundred turns can be used.
 As shown in FIGS. 3A to 3C, in the magnet assembly 33b, the two pairs of
 permanent magnets 33d, which oppose each other through the coil winding
 33c, are opposite in polarity and form a magnetic circuit in which the
 magnetic fluxes formed by the respective pairs of permanent magnets are
 opposite in direction. That is, as shown in FIGS. 3A to 3C, a pair of
 permanent magnets having an N-S arrangement is placed opposite to a pair
 of permanent magnets having an S-N arrangement.
 When a current is fed through the coil winding 33c placed in the magnetic
 field to cross the direction of magnetic fluxes at right angles, a thrust
 is generated between the coil assembly 33a and the magnet assembly 33b in
 a direction perpendicular to the direction of magnetic flux and coil
 current direction. Referring to FIGS. 3A to 3C, when a current is fed
 through the coil winding 33c in the direction indicated by an arrow i, a
 thrust proportional to the coil current and the magnetic flux density in
 the space where the coil winding 33c is present acts on the coil assembly
 33a and the magnet assembly 33b in the direction indicated by an arrow f.
 This electromagnetic linear motor can, therefore, be used as an actuator
 for applying a control force to the anti-vibration table 1 by mounting the
 coil assembly 33a on the apparatus installation pedestal on which this
 anti-vibration apparatus is installed or a member firmly fastened to the
 apparatus installation pedestal and also mounting the magnet assembly 33b
 on the anti-vibration table 1 or a member firmly fastened to the
 anti-vibration table 1.
 An electromagnetic linear motor of this type that uses a Lorentz force has
 no mechanical interference mechanism between the coil assembly and the
 magnet assembly, and these assemblies are mechanically isolated from
 vibrations in a noncontact state. An anti-vibration apparatus is required
 to minimize transmission of vibrations between two structures, i.e., the
 anti-vibration table and the apparatus installation pedestal. An
 electromagnetic linear motor of this type can be suitably used in this
 field of anti-vibration techniques. In addition, the electromagnetic
 linear motor having this arrangement can be formed by a flat structure to
 improve the spatial arrangement efficiency, thereby further facilitating
 mounting of the electromagnetic linear motor in the anti-vibration unit.
 In the anti-vibration apparatus disclosed in the present invention, each
 electromagnetic linear motor is preferably used as a moving magnet type
 linear motor obtained by mounting a coil assembly on the apparatus
 installation pedestal or a member firmly fastened to the apparatus
 installation pedestal and also mounting a magnet assembly on the
 anti-vibration table 1 or a member firmly fastened to the anti-vibration
 table 1. Since the coil winding has an electric resistance, heat is
 generated when current is fed through it. In consideration of the
 influence of heat on the preciseness of the precision equipment mounted on
 the anti-vibration table 1, the magnet assembly is preferably mounted on
 the anti-vibration table 1 or a member firmly fastened thereto. The coil
 assembly as a heating element is undesirable for mounting on the
 anti-vibration table 1 or a member firmly fastened thereto. This
 arrangement can suppress direct transmission of heat to the precision
 equipment through the members constituting the anti-vibrationunit. This
 allows measures to be mainly taken for transmission of heat through the
 atmosphere in the space where the electromagnetic linear motor is present.
 In addition, when the coil assembly is mounted on the apparatus
 installation pedestal or a member firmly fastened to the apparatus
 installation pedestal, the coil can be located more easily than when the
 coil is mounted on a movable portion. The transmission of heat through the
 atmosphere in the space can be easily suppressed by, for example,
 surrounding the electromagnetic linear motor with a metal member having a
 large heat capacity and drawing the air in the space.
 A plurality of electromagnetic linear motors each identical to the one
 described above is arranged on each portion of the anti-vibration table 1.
 These electromagnetic linear motors may be formed into several groups, and
 a plurality of electromagnetic linear motors included in the same group
 may be driven by the same driving command signal. In addition, the
 plurality of electromagnetic linear motors driven by the same driving
 command signal may be further formed into several groups (at least one
 group), and a plurality of electromagnetic linear motors included in the
 same group may electrically be connected in parallel or series to be
 driven.
 It is preferable that the axis of action of each pneumatic actuator almost
 coincides with that of each electromagnetic linear motor in both the
 vertical and horizontal directions.
 The operation of the anti-vibration unit 50 will be described next.
 FIG. 4 schematically shows the control system of the anti-vibration unit 50
 in the horizontal direction in this embodiment. The control system in the
 vertical direction has the same arrangement as that in the horizontal
 direction.
 The anti-vibration unit 50 is operated by driving the vertical pneumatic
 actuator 21, the horizontal pneumatic actuator 22, the vertical linear
 motor 31, and the horizontal linear motor 32 on the basis of signals from
 a vertical displacement sensor 25a, a horizontal displacement sensor 25b,
 the vertical vibration sensor 26a, the horizontal vibration sensor 26b,
 and other devices.
 As the vertical displacement sensor 25a and the horizontal displacement
 sensor 25b, oscillation type displacement sensors such as eddy current
 sensors can be used. As the vertical vibration sensor 26a and the
 horizontal vibration sensor 26b, acceleration sensors can be used. The
 sensors are not limited to the displacement sensor, and a vibration sensor
 and maybe included with the velocity sensor. Especially, it is possible to
 concomitantly use the velocity sensor and acceleration sensor.
 &lt;Displacement Control&gt;
 A displacement control operation to be performed on the basis of output
 signals from the vertical displacement sensor 25a and the horizontal
 displacement sensor 25b will be described first. In this case, this
 operation will be referred to as displacement control for the sake of
 descriptive convenience. The vertical and horizontal displacements of the
 anti-vibration table 1 or the anti-vibration unit 50 firmly fastened to
 the anti-vibration table 1 are respectively detected by the vertical
 displacement sensor 25a and the horizontal displacement sensor 25b. The
 resultant detection signals are input to a compensation operation means 40
 to calculate difference signals between the target values of displacements
 with respect to the reference position of the anti-vibration table 1 and
 the output signals from the vertical displacement sensor 25a and the
 horizontal displacement sensor 25b, i.e., deviation signals with respect
 to the vertical and horizontal reference positions. The calculated
 deviation signals are input to a deviation compensation operation means 41
 and compensated for. The deviation compensation operation means 41
 performs a compensation operation for the deviation signals by a control
 method such as a PID compensation (proportional/integral/differential
 compensation) method. In this displacement control operation, in
 particular, a compensation operation such as PI compensation
 (proportional/integral compensation) including an integral operation is
 preferably performed to set the anti-vibration table 1 at a predetermined
 target position without any deviation. The deviation compensation signals
 obtained as a result of the above compensation operation are input to the
 above actuators, i.e., the vertical pneumatic actuator 21 and the
 horizontal pneumatic actuator 22 or the driving circuits for the vertical
 linear motor 31 and the horizontal linear motor 32 so as to drive the
 respective actuators, thereby properly setting the anti-vibration table 1
 at the predetermined target position.
 Note that in this displacement control operation, a thrust must be steadily
 applied to the anti-vibration table 1 to keep the anti-vibration table 1
 at a predetermined position. In order to keep the anti-vibration table 1
 at a predetermined position in the vertical direction, in particular, a
 thrust large enough to support the anti-vibration table 1 is required for
 each actuator. The weight of the anti-vibration table 1 must be increased
 to improve the anti-vibration effect, and a large thrust must steadily be
 generated to maintain the anti-vibration table 1 at a predetermined
 position.
 However, the electromagnetic linear motors used as the vertical linear
 motor 31 and the horizontal linear motor 32 generate heat when currents
 are fed through the coils. When the electromagnetic linear motors are used
 in a displacement control operation to steadily generate large thrusts, in
 particular, the amount of heat generated by the coils increases, and the
 heat is transferred to the anti-vibration unit 50 and the anti-vibration
 table 1, thereby increasing the temperature of each portion.
 The anti-vibration apparatus disclosed in the present invention aims at
 mounting precision equipment. In this field, however,
 contraction/expansion of members due to changes in the temperatures of the
 anti-vibration table 1 and the device mounted thereon greatly affects the
 measurement precision and operation precision of the precision equipment.
 It is, therefore, preferable that pneumatic actuators such as the vertical
 pneumatic actuator 21 and the horizontal pneumatic actuator 22 as shown in
 FIG. 4 be used as actuators used in a displacement control operation or
 used to generate steady thrusts, and be used together with electromagnetic
 linear motors such as the vertical linear motor 31 and the horizontal
 linear motor 32 to damp and settle transitional vibrations produced upon
 positioning of the device.
 &lt;Vibration Control&gt;
 A vibration control operation to be performed on the basis of output
 signals from the vertical vibration sensor 26a and the horizontal
 vibration sensor 26b will be described next. In this case, this operation
 will be referred to as vibration control for the sake of descriptive
 convenience. First of all, the vertical and horizontal vibrations of the
 anti-vibration table 1 are respectively detected by the vertical vibration
 sensor 26a and the horizontal vibration sensor 26b. The resultant
 detection signals are input to a vibration compensation operation means 42
 and compensated for. As the vertical vibration sensor 26a and the
 horizontal vibration sensor 26b, acceleration sensors are generally used.
 In this embodiment, acceleration sensors are used as the vertical
 vibration sensor 26a and the horizontal vibration sensor 26b.
 In this vibration control operation, arithmetic processing such as
 proportional compensation and integral compensation or PI compensation
 (proportional/integral compensation) is performed for the signals obtained
 by the vertical vibration sensor 26a and the horizontal vibration sensor
 26b. A vibration control operation is implemented by a method of feeding
 back a mass term by applying a force proportional to the acceleration of
 the anti-vibration table 1 to the anti-vibration table 1, a method of
 feeding back a damping term by applying a force proportional to the
 velocity of the anti-vibration table 1 to the anti-vibration table 1, a
 method combining the above methods, or the like.
 A vibration control operation will be described below by exemplifying the
 method of damping the vibrations of the anti-vibration table 1 by applying
 a force proportional to the velocity of the anti-vibration table 1 to the
 anti-vibration table 1. In general, different compensation operation
 methods are used in a case wherein the vertical pneumatic actuator 21 and
 the horizontal pneumatic actuator 22 are used as actuators for
 implementing a vibration control operation and a case wherein the vertical
 linear motor 31 and the horizontal linear motor 32 are used for such
 actuators. Each compensation method will, therefore, be described below.
 &lt;Control of Pneumatic Actuators&gt;
 A control operation using the vertical pneumatic actuator 21 and the
 horizontal pneumatic actuator 22 will be described first. Assume that the
 response speed of each pneumatic actuator is very low, and the response
 frequency of a thrust generated in response to a driving command signal to
 the actuator is lower than the natural frequency of the vibration system
 constituted by the anti-vibration table 1 and the support mechanism for
 damping/supporting the anti-vibration table 1 by 10 times or more. The
 pneumatic actuator functions as an actuator having integral
 characteristics in a frequency region near the natural frequency of the
 vibration system of the anti-vibration table 1. A force proportional to
 the velocity of the anti-vibration table 1 can, therefore, be applied to
 the anti-vibration table 1 in the main band, i.e., the frequency region
 near the natural frequency of the vibration system of the anti-vibration
 table 1, by detecting the accelerations of the anti-vibration table 1
 through the vertical vibration sensor 26a and the horizontal vibration
 sensor 26b, and feeding back the data obtained by performing proportional
 compensation (gain compensation) for the detected accelerations to the
 vertical pneumatic actuator 21 and the horizontal pneumatic actuator 22.
 Since each actuator has integral characteristics, a thrust proportional to
 the velocity of the anti-vibration table 1 is fed back to the
 anti-vibration table 1.
 Assume that the response speed of each pneumatic actuator is very high, and
 the response frequency does not differ much from the natural frequency of
 the vibration system constituted by the anti-vibration table 1 and the
 support mechanism for damping/supporting the anti-vibration table 1. In
 this case, acceleration signals obtained from the vertical vibration
 sensor 26a and the horizontal vibration sensor 26b may be compensated for
 by using a PI compensation (proportional/integral compensation) device in
 which parameters are set to have a zero point at the response frequency of
 each pneumatic actuator, and the resultant signals may be fed back to the
 vertical pneumatic actuator 21 and the horizontal pneumatic actuator 22.
 With this operation, the zero point of the PI compensation device cancels
 out the pole (eigenvalue) of each pneumatic actuator, and a combination of
 the outputs from the PI compensation device and the pneumatic actuator
 becomes an integral element. As a result, a force proportional to the
 integral of the accelerations of the anti-vibration table 1, i.e., a
 velocity proportional signal, is applied to the anti-vibration table 1.
 &lt;Control of Linear Motors&gt;
 A vibration control operation using the vertical linear motor 31 and the
 horizontal linear motor 32 will be described next. In general, the
 response frequencies of thrusts generated by electromagnetic linear motors
 such as the vertical linear motor 31 and the horizontal linear motor 32 in
 response to driving command signals are much higher than the natural
 frequency of the vibration system constituted by the anti-vibration table
 1 and the support mechanism for damping/supporting the anti-vibration
 table 1. The natural frequency of the vibration system constituted by the
 anti-vibration table 1 and the support mechanism for damping/supporting
 the anti-vibration table 1 ranges from several Hz to a maximum of about
 several tens of Hz. On the other hand, an electromagnetic linear motor has
 a relatively large inductance if the number of turns of the coil is large.
 When this motor is driven by a circuit of a voltage control type, the
 response frequency may sometimes become 100 Hz or less. In general,
 however, the electromagnetic linear motor is driven by a driving circuit
 with current feedback. In this case, owing to the effect of current
 feedback, a response frequency of 100 Hz or more can be easily realized.
 It can, therefore, be assumed that the electromagnetic linear motor has
 gain characteristics in the frequency region near the natural frequency of
 the vibration system of the anti-vibration table 1. As a consequence, a
 force proportional to the velocity of the anti-vibration table 1 can be
 applied to the anti-vibration table 1 by performing integral compensation
 for the accelerations of the anti-vibration table 1 which are detected by
 the vertical vibration sensor 26a and the horizontal vibration sensor 26b,
 and feeding back the resultant data to the vertical linear motor 31 and
 the horizontal linear motor 32.
 As shown in FIG. 4, in the anti-vibration apparatus disclosed in the
 present invention, a vibration control operation based on acceleration
 signals obtained from the anti-vibration table 1 and the like is
 preferably performed mainly by using the electromagnetic linear motors
 having fast-response characteristics. This is because control must be
 performed by following a driving reaction force of the X-Y stage, which
 operates at a high speed/acceleration and high response speed. If
 vibration control is performed by using the pneumatic actuators, which are
 lower in response speed than the electromagnetic linear motors, the
 high-speed/-acceleration operation of the X-Y stage cannot be properly
 followed. In addition, the apparatus may be forced to use the pneumatic
 actuators beyond their capacities, resulting in undesirable variations in
 apparatus characteristics. In a vibration control operation, therefore, it
 is preferable that the electromagnetic linear motors be used or the load
 ratio of the electromagnetic linear motors to the pneumatic actuators be
 increased.
 In this embodiment, a displacement control operation for the anti-vibration
 table 1 is preferably performed by extracting deviation signals with
 respect to the reference positions in the respective motion modes of the
 anti-vibration table 1, e.g., translation and rotation, from target values
 in the respective motion modes of the anti-vibration table 1, e.g.,
 translation and rotation, with respect to the reference positions and
 output signals from a plurality of displacement detection means for
 detecting the vertical and horizontal displacements of the anti-vibration
 table 1 with respect to the reference positions, performing a compensation
 operation for the signals, and distributing the resultant operation mode
 compensated signals to the respective actuators that are arranged at each
 portion of the anti-vibration table 1 to apply control forces to the
 anti-vibration table 1.
 Likewise, in this embodiment, a vibration control operation for the
 anti-vibration table 1 is preferably performed by extracting vibration
 signals for the respective motion modes of the anti-vibration table 1,
 e.g., translation and rotation, from output signals form a plurality of
 vibration detection means for detecting the vertical and horizontal
 vibrations of the anti-vibration table 1, performing a compensation
 operation for the signals, and distributing the resultant motion mode
 compensated signals to the respective actuators that are arranged at each
 portion of the anti-vibration table 1 to apply control forces to the
 anti-vibration table 1.
 A control operation for each actuator based on signals from the above
 displacement detection means, vibration detection means, and other devices
 will be described next.
 The manner in which the above electromagnetic linear motors or pneumatic
 actuators are driven by performing an appropriate compensation operation
 based on signals from a control means or the operation state of a device
 having a driving means such as an X-Y stage and mounted on the
 anti-vibration table 1 will be described first.
 Assume that a device having a driving means such as an X-Y stage 45 is
 mounted on the anti-vibration table 1, as shown in FIG. 4. This X-Y stage
 45 can move in two arbitrary directions, i.e., the X and Y directions,
 using linear mechanisms constituted by electromagnetic motors and ball
 screws or electromagnetic linear motors. Each electromagnetic motor or
 electromagnetic linear motor for driving the X-Y stage 45 is driven by an
 X-Y stage driving circuit 47 on the basis of a signal from an X-Y stage
 control means 46.
 In this case, a control operation is performed by using a feedforward
 compensation operation means for receiving a signal from the X-Y stage
 control means 46 or a signal associated with the driven state of the X-Y
 stage, performing appropriate arithmetic processing for the signal, and
 sending the processing result to the driving circuit for the corresponding
 actuator for applying a control force to the anti-vibration table 1.
 The following two feedforward compensation operation methods are available.
 In the first method, a compensation operation is performed to cancel out a
 driving reaction force produced when the X-Y stage 45 is driven. In the
 second method, a compensation operation is performed to correct the tilt
 of the anti-vibration table 1 due to load movement by compensating for a
 change in the moment balance of the anti-vibration table support mechanism
 upon movement of the load of the X-Y stage 45 over the anti-vibration
 table 1.
 The former method can be implemented by performing an appropriate
 compensation operation by using bandpass filters and the like in a first
 feedforward compensation operation means 43, mainly on the basis of
 signals proportional to the accelerations of the X-Y stage 45 or driving
 reaction forces of the X-Y stage, so as to apply forces proportional to
 the accelerations or driving reaction forces to the anti-vibration table 1
 in a desired control frequency band. The compensated signals obtained as
 outputs from the first feedforward compensation operation means 43 are
 sent to the electromagnetic linear motors such as the vertical linear
 motor 31 and the horizontal linear motor 32 to cancel out the driving
 reaction forces generated when the X-Y stage 45 is driven. To cope with
 the high-speed/-acceleration operation of the X-Y stage 45, the actuators
 to be used must be electromagnetic linear motors.
 The latter method can be implemented by performing an appropriate
 compensation operation using bandpass filters and the like in a second
 feedforward compensation operation means (not shown in FIG. 4) mainly on
 the basis of signals proportional to the displacements of the X-Y stage
 45. The compensated signals obtained as outputs from the second
 feedforward compensation operation means are sent to pneumatic actuators
 such as the vertical pneumatic actuator 21 and the horizontal pneumatic
 actuator 22 to compensate for changes in the moment balance of the
 anti-vibration table support mechanism due to movement of the load of the
 X-Y stage 45 over the anti-vibration table 1. In this operation, a force
 must be steadily generated to maintain the steady moment balance of the
 support mechanism which depends on the position of the X-Y stage 45, and
 hence the pneumatic actuators are preferably used.
 In these control operations, similar to the displacement and vibration
 control operations described above, it is preferable that pieces of
 information about the forces, accelerations, and displacements produced
 upon driving of the X-Y stage be converted into signals corresponding to
 the respective motion modes of the anti-vibration table 1, e.g.,
 translation and rotation, an appropriate compensation operation be
 performed in units of motion modes, and the resultant compensated signals
 be distributed to the respective actuators that are arranged for each
 portion of the anti-vibration table 1 to apply control forces to the
 anti-vibration table 1.
 The apparatus disclosed in the present invention may include a control
 system for detecting vibrations of an apparatus installation pedestal such
 as a floor on which the anti-vibration system constituted by the
 anti-vibration table 1 and the support mechanism for damping/supporting
 the anti-vibration table, appropriately compensating for the resultant
 detection signals, and feedforward-controlling the compensated signals to
 the actuators for applying control forces to the anti-vibration table 1 in
 addition to the control system of driving the actuators for applying
 control forces to the anti-vibration table 1 by performing an appropriate
 compensation operation based on the control loop for the above position
 control operation and vibration control operation, the operation state of
 a device having a driving means such as an X-Y stage and mounted on the
 anti-vibration table 1, or signals from a control means for the device.
 According to this embodiment, the heavy anti-vibration table on which
 precision equipment and the like are mounted can be supported at a
 predetermined position by using the pneumatic actuators that can steadily
 generate large thrusts, and the high-speed/-acceleration operation of a
 mounted device such as an X-Y stage can be properly coped with by using
 the electromagnetic actuators with fast-response characteristics, thus
 realizing quick vibration control. Therefore, both the anti-vibration
 performance and vibration control performance requirements can be
 satisfied, which cannot be satisfied by the conventional anti-vibration
 table.
 In this embodiment, both the anti-vibration performance and vibration
 control performance requirements in the horizontal direction can be
 satisfied as well as in the vertical direction by using the pneumatic
 actuators, each having a backlash in a direction perpendicular to the
 direction in which a force is generated, in combination of the noncontact
 type electromagnetic linear motors. In addition, since the pneumatic
 actuators having bellows structures are used, the respective components of
 the anti-vibration apparatus can be made more compact and can be
 efficiently arranged, thus realizing an integral anti-vibration apparatus
 as a unit. In this embodiment, the pneumatic actuators and the
 electromagnetic linear motors are arranged in both the vertical and
 horizontal directions. Assume, however, that there is a specific
 displacement mode or vibration mode to be removed in a given direction,
 and the mode can be removed by using only a pneumatic actuator or
 electromagnetic linear motor. In this case, both the pneumatic actuator
 and the electromagnetic linear motor need not be set in this direction.
 In this embodiment, since the coil winding of each electromagnetic actuator
 is mounted on a member on the apparatus installation pedestal side, the
 adverse effect on the precision equipment on the anti-vibration table
 owing to a temperature rise caused by the heat generated by the coil can
 be reduced. In addition, the coil windings can be easily located and can
 be suitably used for an anti-vibration/damping apparatus for precision
 equipment. Furthermore, since the linear motors used in this embodiment
 have flat structures, the degree of freedom in the spatial arrangement of
 the apparatus is higher than that in a case wherein electromagnetic motors
 such as cylindrical voice coil motors are used. Therefore, an active
 anti-vibration apparatus having a compact structure can be realized.
 Second Embodiment
 FIG. 5 is a schematic view showing an active anti-vibration apparatus
 according to the second embodiment.
 A horizontal pneumatic actuator 22 in FIG. 5 is a pneumatic actuator of the
 type having a pre-pressurizing mechanism 24 such as a coil spring
 dynamically parallel to a pneumatic spring 23c. Other components and
 control methods are the same as those in the first embodiment, and hence,
 a description thereof will be omitted.
 A predetermined amount of pre-pressure is kept applied to the
 pre-pressurizing mechanism 24 in a contraction direction at a neutral
 position in the horizontal pneumatic actuator 22. In this embodiment, by
 raising the internal pressure of the pneumatic spring 23c, a force can be
 applied to an anti-vibration table 1 in the +X direction indicated by the
 arrow in FIG. 5. In addition, when the internal pressure of the pneumatic
 spring 23c is decreased, the overall actuator can generate a force in the
 -X direction owing to the elastic force of the pre-pressurizing mechanism
 24 dynamically parallel to the pneumatic spring 23c, although the
 pneumatic spring 23c itself cannot generate any force in the contraction
 direction.
 Although FIG. 5 shows the horizontal pneumatic actuator 22, in an
 anti-vibration unit 50, which corresponds to only one horizontal
 direction, control forces can be applied in a plurality of arbitrary
 directions by using two or more horizontal pneumatic actuators.
 In this embodiment, it is preferable that the axis of action of the
 pre-pressurizing mechanism almost coincides with the axis of action of the
 pneumatic spring. It is also preferable that the axes of action of the
 horizontal linear motors almost coincides with the axis of action of the
 pneumatic actuator. According to this embodiment, the same effects as
 those of the embodiment described above can be obtained. In addition,
 since only one pneumatic spring is required in the horizontal direction,
 piping of the pneumatic spring and installation of a pressure control
 apparatus are facilitated.
 Third Embodiment
 FIGS. 6A and 6B are schematic views showing an electromagnetic linear motor
 used in an active anti-vibration apparatus according to the third
 embodiment.
 The linear motor in the above embodiment is a single-phase linear motor
 having one coil winding. The linear motor in this embodiment uses two coil
 windings.
 The electromagnetic linear motor in these figures is comprised of a coil
 assembly 34a including two coil windings and a magnet assembly 34b having
 four pairs of opposing permanent magnets. This motor is obtained by
 connecting two single-phase linear motors, each described as the first
 example of the electromagnetic linear motor, in series in a thrust
 generating direction. A force in the direction indicated by an arrow f in
 FIG. 6B can be applied between the two assemblies by feeding a current
 through each coil winding in the direction indicated by an arrow i.
 Since the coil and magnet assemblies are integrally formed while ensuring
 thrust characteristics corresponding to the two single-phase linear motors
 described above, the electromagnetic linear motor with this arrangement
 can save the dimensions of portions where these components are mounted.
 Therefore, the dimensions of the space required to mount the
 electromagnetic linear motor on the anti-vibration unit can be further
 reduced.
 In addition, a plurality of electromagnetic linear motors, each identical
 to the one described above, may be arranged at each portion of an
 anti-vibration table 1. In addition, these electromagnetic linear motors
 may be formed into several groups, and a plurality of electromagnetic
 linear motors included in the same group may be driven by the same driving
 command signal. Likewise, these electromagnetic linear motors may be
 arranged at each portion of the anti-vibration table 1. In addition, the
 coil windings of the respective electromagnetic linear motors may be
 formed into several groups, and the coil windings of the electromagnetic
 linear motors included in the same group may be driven by the same driving
 command signal.
 The plurality of electromagnetic linear motors or coil windings driven by
 the same driving command signal may be further formed into several groups
 (at least one group), and a plurality of electromagnetic linear motors or
 coil windings included in the same group may be electrically connected in
 parallel or series to be driven.
 The control system required to drive a plurality of electromagnetic linear
 motors can be simplified by driving the electromagnetic linear motors or
 coil windings in the same group using the same driving signal. In
 addition, the control system for a plurality of linear motors can be
 simplified by electrically connecting the electromagnetic linear motors or
 coil windings in the same group in series or parallel and driving them.
 With the use of the linear motor in this embodiment as each electromagnetic
 linear motor of an active anti-vibration apparatus, the same effects as
 those obtained in the first and second embodiments can be obtained.
 Fourth Embodiment
 FIGS. 7A and 7B are schematic views showing an electromagnetic linear motor
 used in an active anti-vibration apparatus according to the fourth
 embodiment.
 The electromagnetic linear motor in these figures is comprised of a coil
 assembly 35a including two coil windings and a magnet assembly 35b having
 four pairs of opposing permanent magnets. This motor is obtained by
 connecting two single-phase linear motors, each identical to the one in
 the first embodiment, in series in a thrust generating direction so as to
 have an integral structure.
 In the coil assembly 34a of the linear motor in the third embodiment in
 FIGS. 6A and 6B, the magnets with the polarity arrangement "NSNS" are
 arranged opposite to the magnets with the polarity arrangement "SNSN". In
 contrast to this, in the coil assembly 35a of the linear motor in this
 embodiment, the magnets with the polarity arrangement "NSSN" are arranged
 opposite to the magnets with the polarity arrangement "SNNS".
 A thrust in the direction indicated by the direction indicated by an arrow
 f in FIG. 6B can be applied between the two assemblies by feeding a
 current through each coil winding in the direction indicated by an arrow
 i. In this case, to generate thrusts in the same direction, coil currents
 are fed through the two coil windings in different directions.
 FIGS. 8A and 8B are schematic views showing a single-phase linear motor. In
 this single-phase linear motor, coil portions that do not contribute to
 the generation of a thrust in a predetermined direction may generate other
 thrust components owing to the interaction between the coil portions and
 the magnetic field. In this electromagnetic linear motor, the portions
 that contribute to the generation of the thrust in the predetermined
 direction are portions a in FIG. 8B, whereas portions b and c in FIG. 8B
 do not contribute to the generation of the thrust in the predetermined
 direction but generate thrusts between the coil and magnet assemblies in
 the directions indicated by arrows in directions d1, d2, e1, and e2 owing
 to the interaction between the currents flowing through the coil portions
 and the magnetic field generated by the magnet assembly. The directions of
 the arrows show the directions of the thrust where it acts on the coil.
 In this case, if the portions b and c have identical and symmetrical
 shapes, and the magnetic flux distributions at the portions b and c are
 identical, the thrusts as other components indicated by the arrows d1, d2,
 e1, and e2 cancel each other. In practice, however, the leading portion of
 the coil winding from the start or end of the winding to the lead wire of
 the electromagnetic linear motor is sometimes processed on the portion b
 or c. As a result, the portions b and c of the coil winding may differ in
 their shapes. In addition, the portions band c of the coil winding often
 differ in their shapes owing to the problem of cost or techniques in the
 manufacture of the coil winding. Furthermore, different magnetic flux
 distributions may appear at the portions b and c owing to the influences
 of variations in magnetization of the permanent magnets arranged on the
 magnet assembly or the positioning precision of the coil and magnet
 assemblies. In this case, other thrust components d1 and d2 generated at
 the portion b differ from other thrust components e1 and e2 generated at
 the portion c. As a result, other thrust components are generated in
 directions other than the thrust direction of the electromagnetic linear
 motor. The other thrust components become larger as the electromagnetic
 linear motor generates a larger thrust.
 Since an electromagnetic linear motor of this type, in particular, has no
 mechanical motion restraint mechanism between the coil and magnet
 assemblies, other thrust components directly become disturbance forces.
 Owing to the structural characteristics of this electromagnetic linear
 motor, these disturbance forces act as moments that cause mainly the coil
 and magnet assemblies to mutually rotate about the magnetic field
 direction.
 In an electromagnetic linear motor of the type described in the third
 embodiment shown in FIGS. 6A and 6B, for the same reason as that described
 above, other thrust components may be generated between the coil and
 magnet assemblies.
 In a linear motor in which permanent magnets with the polarity arrangement
 "NSSN" are arranged opposite to permanent magnets with the polarity
 arrangement "SNNS", like the electromagnetic linear motor in this
 embodiment shown in FIGS. 7A and 7B, when currents are fed through the two
 coils to generate thrusts in the same direction, coil winding portions of
 the two coils that do not contribute to the generation of thrusts in a
 predetermined direction act on the two coil windings in opposite
 directions. As a consequence, the moments generated by these portions act
 in directions to cancel out each other, and hence, the moments generated
 between the coil and magnet assemblies can be reduced. Especially, when
 the two coil windings are arranged in magnetic fields with similar
 magnetic flux densities, and equal currents are fed through the two coil
 windings, components, i.e., moments, other than the above thrusts can be
 almost canceled out. When, therefore, an electromagnetic linear motor is
 to be applied to an anti-vibration unit as in this embodiment of the
 present invention, a motor of the type described above is preferably used,
 in which magnets with the polarity arrangement "NSSN" are arranged
 opposite to magnets with the polarity arrangement "SNNS", and two coils
 are arranged between these magnet arrays.
 This embodiment can obtain the same effects as those described in the first
 to third embodiments, in addition to the effects described above.
 Fifth Embodiment
 FIGS. 9A and 9B are schematic views showing an electromagnetic linear motor
 used in an active anti-vibration apparatus according to the fifth
 embodiment.
 In this embodiment, as shown in these figures, the motor is comprised of
 two coil windings and three pairs of permanent magnets. This motor is of
 the type obtained by integrating the two electromagnetic linear motors
 described above. More specifically, magnets with the polarity arrangement
 "NSSN" are arranged opposite to magnets with the polarity arrangement
 "SNNS", and the two middle permanent magnets of each magnet array are
 integrated into one unit. That is, the permanent magnets with the polarity
 arrangement "NSN" are arranged opposite to the permanent magnets with the
 polarity arrangement "SNS" to form a magnetic circuit.
 This structure can reduce the number of parts, i.e., permanent magnets
 required, and hence contributes to a reduction in cost as compared with
 the above electromagnetic linear motor using four pairs of permanent
 magnets.
 Note that when the electromagnetic linear motor having these two coil
 windings is to be used, this motor is preferably applied as a moving
 magnet type to the apparatus such that the coil assembly is mounted on an
 apparatus installation pedestal or a member firmly fastened to the
 pedestal, and the magnet assembly is mounted on an anti-vibration table 1
 or a member firmly fastened to the anti-vibration table 1.
 This embodiment can obtain the same effects as those described in the first
 to fourth embodiments, in addition to the effects described above.
 Sixth Embodiment
 FIGS. 10A and 10B are schematic views showing an electromagnetic linear
 motor used in an active anti-vibration apparatus according to the sixth
 embodiment.
 In this embodiment, interpole magnets 37 are used in the magnet assembly of
 the single-phase linear motor.
 As in this embodiment, when interpole magnets are added to the main magnets
 in the magnetic circuit of the electromagnetic linear motor, the magnetic
 flux distribution of the magnetic field in which the coil assembly is
 present can be adjusted more properly, and the magnetic flux in the space
 where the coil is present can be made more uniform and stronger. This can
 increase the thrust constant of the electromagnetic linear motor.
 Referring to FIGS. 10A and 10B, although the single-phase linear motor is
 used, the present invention is not limited to this. Interpole magnets like
 those in this embodiment can be applied to an electromagnetic linear motor
 having a plurality of coil windings as in the third to fifth embodiments
 described above.
 This embodiment can obtain the same effects as those described in the first
 to fifth embodiments, in addition to the above effects.
 Seventh Embodiment
 An embodiment of a scan type exposure apparatus using the anti-vibration
 apparatus of the above embodiment will be described next with reference to
 FIG. 11.
 A lens barrel base plate 96 is supported on a floor or pedestal 91 through
 an anti-vibration unit 50. The lens barrel base plate 96 supports a
 reticle base plate 94 and a projection optical unit 97 positioned between
 a reticle stage 95 and a wafer stage 93. The wafer stage 93 is supported
 on a stage base plate 92 supported by the floor or pedestal 91. The wafer
 stage 93 mounts and positions a wafer. The reticle stage 95 is supported
 on the reticle base plate 94 supported by the lens barrel base plate 96,
 and can move while mounting a reticle. An illumination optical unit 99
 emits exposure light to expose the reticle mounted on the reticle stage 95
 onto the wafer on the wafer stage 93.
 Note that the wafer stage 93 is scanned in synchronism with the reticle
 stage 95. While the reticle stage 95 and the wafer stage 93 are scanned,
 their positions are continuously detected by interferometers, and the
 resultant data are respectively fed back to driving units for the reticle
 stage 95 and the wafer stage 93. With this operation, the scan start
 positions of the two stages can be accurately synchronized, and the
 scanning speed in a constant-speed scanning region can be controlled with
 high precision.
 With the use of the active anti-vibration apparatus of the above
 embodiment, this embodiment properly has both the anti-vibration
 performance against external vibrations affecting the lens barrel base
 plate and the stage base plate 92 and the proper vibration control
 performance against vibrations generated in the translation and rotation
 directions upon movement of the reticle stage and the wafer stage. This
 embodiment can, therefore, perform high-speed, high-precision exposure.
 In this embodiment, the stage base plate 92 and the lens barrel base plate
 96 are independently arranged, and the anti-vibration apparatuses are used
 for the respective components. Even if, however, a lens barrel base plate
 and the stage base plate are integrally formed and mounted on the same
 anti-vibration apparatus, the same effects as those described above can be
 obtained by using the active anti-vibration apparatus of the above
 embodiment as this anti-vibration apparatus. That is, high-speed,
 high-precision exposure can be performed. In this case, since the stage
 base plate for supporting a wafer and the reticle base plate for
 supporting a reticle are supported on the floor through the same
 anti-vibration unit, the anti-vibration unit may be controlled by using a
 feedforward compensation operation means for sending signals to driving
 circuits for actuators for applying control forces on the basis of signals
 from stage control means for both the wafer and reticle stages.
 Eighth Embodiment
 An embodiment of a semiconductor device manufacturing method using the
 above exposure apparatus will be described next. FIG. 12 is a flow chart
 showing a manufacturing process for a semiconductor device (e.g., a
 semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, or
 the like). In step 11 (circuit design), the circuit of a semiconductor
 device is designed. In step 12 (mask formation), a mask on which the
 designed circuit pattern is formed is formed. In step 13
 (wafermanufacture), a wafer is manufactured by using a material such as
 silicon. In step 14 (waferprocess), which is referred to as a pre-process,
 the prepared mask and wafer are used to form an actual circuit on the
 wafer using a lithographic technique. In step 15 (assembly), which is
 referred to as a post-process, a semiconductor chip is formed by using the
 wafer manufactured in step 14. This process includes steps such as the
 assembly step (dicing and bonding) and the packaging step (chip
 encapsulation). In step 16 (test), tests such as an operation test and a
 durability test are performed with respect to the semiconductor device
 manufactured in step 15. The semiconductor device is completed through
 these steps and shipped (step S17).
 FIG. 13 is a flow chart showing the above wafer manufacturing process in
 detail. In step 21 (oxidation), the upper surface of a wafer is oxidized.
 In step 22 (CVD), an insulating film is formed on the upper surface of the
 wafer. In step 23 (electrode formation), an electrode is formed on the
 wafer by vapor deposition. In step 24 (ion implantation), ions are
 implanted into the wafer. In step 25 (resist process), the wafer is coated
 with a photoresist. In step 26 (exposure), the circuit pattern on the mask
 is printed/exposed on the wafer by the above exposure apparatus. In step
 27 (development), the exposed wafer is developed. In step 28 (etching),
 portions other than the developed resist image are removed. In step 29
 (resist peeling), the unnecessary resist after etching is removed. By
 repeating these steps, multiple circuit patterns can be formed on the
 wafer. A high-integration semiconductor device, which is difficult to
 manufacture in the prior art, can be manufactured by using the
 manufacturing method of this embodiment.
 The anti-vibration apparatus according to the present invention can
 actively reduce vibrations of an object by generating forces in the
 vertical and horizontal directions against the anti-vibration table. In
 addition, the respective components of this apparatus can be made more
 compact and efficiently arranged to provide a compact anti-vibration
 apparatus.
 In addition, since vibrations of the components of the exposure apparatus
 of the present invention are damped with high precision, the apparatus can
 perform high-speed, high-precision exposure.
 Furthermore, a device can be manufactured at high speed with high precision
 by the device manufacturing method of the present invention.
 Moreover, according to the anti-vibration method of the present invention,
 vibrations of a damped/supported object can be accurately damped and
 eliminated in the vertical and horizontal directions, and vibrations of
 the equipment mounted on the anti-vibration apparatus can be accurately
 damped and eliminated in the vertical and horizontal directions. In
 addition, the anti-vibration apparatus can damp vibrations of a mounted
 device by using feedforward-controlling, that is implimented by
 compensating for the values of signals of the equipment mounted on the
 anti-vibration apparatus and driving the actuators on the basis of the
 compensated signals. The present invention is not limited to the above
 embodiments and various changes and modifications can be made within the
 spirit and scope of the present invention. Therefore, to appraise the
 public of the scope of the present invention, the following claims are
 made.