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Description  |
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FIELD OF THE INVENTION AND RELATED ART
This invention relates to a supporting device and, more particularly, to a supporting device suitably usable in an X-ray exposure apparatus, for example, used with a light source such as synchrotron radiation light, wherein a light source and an
exposure apparatus are disposed with respect to different positional references.
Increasing capacity in a semiconductor memory has forced improvements in fine patterning techniques in semiconductor device manufacturing apparatuses.
One measure for an improvement in the fine patterning technique is an X-ray exposure apparatus used with a light source of synchrotron radiation light (Japanese Laid-Open Patent Application Laid-Open No. 2-100311). However, in such an X-ray
exposure apparatus, an electron accumulating ring which is a source of synchrotron radiation light is disposed with respect to a positional reference different from that of the exposure apparatus and, therefore, use of an attitude control device for
maintaining constant attitude of the exposure apparatus is necessary to hold the positional relationship between the electron accumulating ring and the exposure apparatus.
FIGS. 21A and 21B are schematic views of a known example of an attitude control device for an X-ray exposure apparatus.
This attitude control device includes a vacuum chamber 101 having accommodated therein a wafer stage (movable portion) 102 which is moved along an X-axis rail 115 and a Y-axis rail 116 by means of an actuator means, not shown. The vacuum chamber
101 is floatingly supported by first, second and third air springs 108.sub.1, 108.sub.2 and 108.sub.3 on a main frame 114. By supplying air from first, second and third pumps 112.sub.1, 112.sub.2 and 112.sub.3 (the third pump 112.sub.3 is not shown) to
the air springs 108.sub.1, 108.sub.2 and 108.sub.3, respectively, in accordance with the tilt of the vacuum chamber 101, the attitude of the vacuum chamber 101 can be held constant.
More specifically, the vacuum chamber 101 is connected to a supporting reference plate 103 through two supporting rods 104.sub.1 and 104.sub.2 extending through a top plate of the main frame 114, and the vacuum chamber is supported between the
top plate of the main frame 114 and the supporting reference plate 103, by means of the air springs 108.sub.1, 108.sub.2 and 108.sub.3 located at left and right positions on the rearward side and at a center position on the forward side, respectively, as
viewed in FIG. 21B. Also, for detection of displacement in the Y-axis direction of the top plate of the supporting reference plate 103 on which the air springs 108.sub.1 -108.sub.3 are mounted, there are provided first, second and third displacement
sensors 118.sub.1, 118.sub.2 and 118.sub.3 which are mounted on first, second and third displacement detection reference plates 106.sub.1, 106.sub.2 and 106.sub.3, respectively, so as to contact the top surface of the supporting reference plate 103. The
first to third displacement detection reference plates are mounted on the top plate of the main frame 114. Further, to the air springs 108.sub.1 -108.sub.3, there are provided first, second and third piping means 113.sub.1, 113.sub.2 and 113.sub.3 (the
third piping means 113.sub.3 is not shown) each for coupling an associated one of the air springs 108.sub.1 -108.sub.3 to a corresponding one of the pumps 112.sub.1 -112.sub.3. First, second and third valves 111.sub.1, 111.sub.2 and 111.sub.3 each is
interposed in a corresponding one of the piping means 113.sub.1 -113.sub.3 and it is controlled in response to an output signal from a corresponding one of the displacement sensors 118.sub.1 -118.sub.3.
SUMMARY OF THE INVENTION
However, this type of attitude control device involves a first problem peculiar to a driving system and resulting from negative feedback of a positional deviation of the vacuum chamber 101 to the opening of the three valves 111.sub.1 -111.sub.3
and a second problem concerning the system as a whole and resulting from control of the attitude of the vacuum chamber by the three air springs 108.sub.1 -108.sub.3. Details of these two problems will be explained, below:
(a) The problem peculiar to the driving system:
For simplicity, a case wherein as shown in FIG. 22 a member 120 having a mass "m" is supported by an air spring 121 with a sectional area "S" and a height "h", is considered.
If the pressure and volume of the air spring 120 and the mole number of the air are denoted by Pn, Vn and Nn, respectively, and if a pressure change and a volume change of the air spring when vibrated and a change in mole number of the air are
denoted by p, v and n, respectively, and further if the displacement of the supported member 120 is denoted by x, then an equation of motion and an equation of state such as follows are obtained:
Also, if the atmospheric pressure is denoted by P.sub.0 and the flow rate of the air at a pressure of P.sub.0 is denoted by Q, then a continuous equation such as follows is obtained:
wherein
Therefore, by simplifying equation (2) while disregarding the minute term of p.multidot.v, the following equation is obtained:
Therefore, with the negative feedback of the displacement x of the supported member 120 to a valve (not shown) of the air spring 120, the flow rate Q of the air of the pressure P.sub.0, which can be approximated as follows, results:
An equation obtainable by substituting equation (6) into equation (5) is one with a third story with respect to the displacement x but, since it has no second story with respect to the displacement x, it necessarily has an unstable pole.
Also, while actually the air spring 121 itself has a small damping resistance, the quantity c/m is so small relative to the damping coefficient that it has substantially no effect. The oscillation may occur or, alternatively, vibration damping
time may become longer.
If the damping coefficient c is made larger for quick damping, it causes a high possibility of each transmission of vibration of high frequency during the exposure operation, and the intended effect of vibration insulation is not attainable.
(b) The problem concerning the system as a whole:
An approximated structure of the whole system of the attitude control device shown in FIG. 21A may be such as illustrated in FIG. 23. More specifically, the vacuum chamber on which the wafer stage 102 is mounted is supported by the first to
third air springs 108.sub.1 -108.sub.3 through the two supporting rods 104.sub.1 and 104.sub.2 and the supporting reference plate 103.
Here, the first air spring 108.sub.1 is connected to the supporting reference plate 103 by means of a universal joint 202.sub.1, through a spring element 200.sub.1 in the X-axis direction in the drawing as well as a spring element 201.sub.1.
This is also true with the case of the second air spring 108.sub.2 and the third air spring 108.sub.3.
When the wafer stage 102 is accelerated, due to its reaction force and reaction moment, each of the spring elements 200.sub.1 -200.sub.3 and 201.sub.1 -201.sub.3 of low rigidity receives a large displacement. Since however what can be controlled
with the driving system is only the displacement component in the Y-axis direction in the drawing, as regards the displacement components in the X-axis and Z-axis directions there is no way other than waiting for extinction by natural attenuation. Here,
if the attenuation is made large, then a problem of failure of vibration insulation results.
Further, when static balance is considered, movement of the wafer stage destroys the balance of moment, and each of the spring elements 200.sub.1 -200.sub.3 and 201.sub.1 -201.sub.3 receives a large displacement. The control of a displacement
component in the Y-axis direction and of the angle of rotation about the X-axis or Z-axis involves an additional difficulty since, due to interference between the X-axis and Z-axis displacement components or a change in moment of inertia about each axis,
in addition to the above-described problem peculiar to the driving system, the system becomes non-linear.
It is accordingly an object of the present invention to provide a supporting device by which the attitude of a member to be supported can be held with high precision even when a movable portion provided within the supported member moves.
In accordance with an aspect of the present invention, there is provided a supporting device for supporting a member having an inside movable portion, wherein the device comprises a supporting reference plate on which the member is to be placed,
and three sets of driving mechanisms each being disposed between a main frame and the supporting reference plate and each having high-rigidity displacement providing means and low-rigidity supporting means of low damping factor, disposed in series.
In accordance with another aspect of the present invention, there is provided a supporting device for supporting a member having an inside movable portion, wherein the device includes a supporting reference plate on which the member is to be
placed, three sets of driving mechanisms each being disposed between a main frame and the supporting reference plate and each having high-rigidity displacement providing means and low-rigidity supporting means of low damping factor, disposed in series,
and supporting force predicting means for predicting a supporting force of each low-rigidity supporting means in accordance with the gravity center position of the movable portion, wherein each low-rigidity supporting means is displaced by a
corresponding one of the high-rigidity displacement providing means of the driving mechanisms.
Here, displacement detecting means for detecting the amount of displacement of each high-rigidity displacement providing means of the three sets of driving mechanisms may be provided.
Further, there may be provided a thrust force providing mechanism having a fixed member and a movable member provided out of contact with the fixed member and provided fixedly on the supported member, for providing a thrust force in parallel with
each low-rigidity supporting means of the driving mechanisms, and canceling force predicting means for predicting a force for canceling, with the thrust force providing mechanism, a reaction force and a moment received applied to the supported member
when the movable portion moves, wherein the thrust force providing mechanism is driven in accordance with the force predicted by the canceling force predicting means.
Still further, there may be provided a damping force providing means having a fixed member and a movable member provided out of contact with the fixed member and provided fixedly on the supported member, for providing a damping force to the
supported member.
Further, the device may comprise discriminating means for discriminating the completion of vibration damping of the supported member, and a blocking mechanism for blocking the thrust force providing mechanism and the damping force providing
mechanism in response to the discrimination of the completion of vibration damping by the discriminating means.
Further, the device may comprise moving means for moving the high-rigidity displacement providing means each in a plane perpendicular to the direction in which displacement is produced by a corresponding high-rigidity displacement producing
means, and coupling means for rotatably mounting each low-rigidity Supporting means to the positioning reference plate.
In a supporting means of the present invention, three sets of driving mechanisms each comprising high-rigidity displacement producing means and low-rigidity supporting means disposed in series with the high-rigidity displacement producing means
and having a low damping factor, may be disposed between a main frame and a supporting reference plate on which a member to be supported and having an inside movable portion is placed. For holding the attitude of the supported member when the movable
portion moves, each low-rigidity supporting means may be displaced by means of corresponding high-rigidity displacement producing means. This minimizes initial displacement of the low-rigidity supporting means and, as a result, prevents vibration of the
low-rigidity supporting means.
An attitude control device of the present invention may be equipped with a supporting means and a supporting force predicting means for predicting the supporting force of each low-rigidity supporting means corresponding to the gravity center
position of a movable portion accommodated in the supported member. Each low-rigidity supporting means can be displaced so as to produce supporting forces as predicted by the supporting force predicting means, such that only the application of a
smallest displacement necessary for the control system assures counteracting to the static force resulting from the movement of the movable portion. Therefore, it is possible to hold the attitude of the supported member very precisely.
When a thrust producing mechanism and a canceling force predicting means are provided, it is possible to predict the force with which the reaction force and moment, applied to the supported member during acceleration of the movable portion, is to
be canceled through the thrust producing mechanism, and it is possible for the thrust producing mechanism to produce forces to be applied to the supported member. It is therefore possible to counteract any dynamic force resulting from movement of the
movable portion.
When a damping force producing means is provided, if the low-rigidity supporting means vibrates, it is possible to detect the vibration and to suppress the vibration.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a first embodiment of the present invention.
FIG. 2 is a schematic view of the structure of a vacuum chamber shown in FIG. 1.
FIG. 3 is a schematic view, showing coordinates of a gravity center and coordinates of a gravity center of an X-Y stage, with spring mounting members being taken as respective origins.
FIG. 4 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a second embodiment of the present invention.
FIG. 5 is a schematic view of an inside structure of a vacuum chamber shown in FIG. 4, and shows the manner of mounting to a stage frame of each linear motor.
FIGS. 6A-6C are schematic views, respectively, wherein FIGS. 6A and 6B show the structures of fixing members while FIG. 6C shows the structure of a movable portion.
FIGS. 7A and 7B are schematic views of the structure of the linear motor shown in FIG. 4, wherein FIG. 7A shows the positional relationship between a fixed member and a movable member while FIG. 7B shows the positional relationship between a
permanent magnet and a coil,
FIG. 8 is a schematic view showing the connection of each linear motor of FIG. 4 to a CPU.
FIG. 9 is a schematic view for explaining the distances between each linear motor of FIG. 4 and the gravity centers of the stage and the Y-axis stage.
FIG. 10 is a schematic view of a supporting device according to a third embodiment of the present invention, and shows the connection between a CPU and each coil of linear motors of an attitude control device for an X-ray exposure apparatus,
FIG. 11 is a schematic view of the structure of each coil of FIG. 10.
FIG. 12 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a fourth embodiment of the present invention.
FIG. 13 is an appearance view showing the structure of an air spring housing of FIG. 12.
FIG. 14 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a fifth embodiment of the present invention.
FIG. 15 is a schematic view showing the structure of moving devices.
FIG. 16 is a schematic view showing the positional relationship of a displacement detection reference plate and displacement sensors.
FIG. 17 is a schematic view of the attitude control device of FIG. 14 when equipped with four linear motors.
FIG. 18 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a sixth embodiment of the present invention.
FIGS. 19A and 19B are schematic views of another example of a linear motor, wherein FIG. 19A shows the positional relationship between a fixed member and a movable member while FIG. 19B shows the positional relationship between a permanent magnet
and a coil.
FIG. 20 is a schematic view of another example of a linear motor.
FIGS. 21A and 21B are schematic views of a known example of an attitude control device for an X-ray exposure apparatus, wherein FIG. 21A is a top plan view while FIG. 21B is a front view.
FIG. 22 is a schematic view for explaining a problem peculiar to a driving system of the attitude control device of FIGS. 21A and 21B.
FIG. 23 is a schematic view of an approximated structure of the whole system of the attitude control device of FIGS. 21A and 21B.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 is a schematic view of an attitude control device for an X-ray exposure apparatus, and shows a supporting device according to a first embodiment of the present invention.
This attitude control device comprises constituent elements such as described below.
(a) Stage Frame 526 (FIG. 2):
This is a member to be supported and has a movable portion provided therewithin. Through the attitude control device of this embodiment, it is held at a constant attitude even when the movable portion moves.
As shown in FIG. 2, the stage frame 526 is placed in a vacuum chamber 510 and is supported by a supporting reference plate 530 through two stage frame mounting members 529.sub.1 and 529.sub.2. Disposed inside the stage frame 526 is a stage 520,
as said movable portion, which is movable along X and Y axes of a coordinate system (X-Y-Z) illustrated, with its X-Z plane being on the floor.
The stage 520 is mounted to a Y-axis stage 522 having an X-axis driving device 524.sub.1 disposed therewithin. The stage 520 can be moved in the Y-axis direction illustrated, as a result of movement of the Y-axis stage 522 along two Y-axis
guides 523.sub.1 and 523.sub.2 by a Y-axis driving device 524.sub.2. Also, the stage 520 can be moved in the X-axis direction illustrated, by means of the X-axis driving device 524.sub.1. It is to be noted here that also the Y-axis stage serves as said
movable portion.
Each of the X-axis driving device 524.sub.1 and the Y-axis driving device 524.sub.2 is provided by a ball-screw mechanism of know type, having a combination of a ball screw and a motor.
(b) Supporting Reference Plate 530:
The supporting reference plate 530 is a member on which the vacuum chamber 510 and the stage frame 526 are placed.
(c) Three Sets of Driving Mechanisms:
Each driving mechanism is disposed between the supporting reference plate and the main frame, and each comprises high-rigidity displacement producing means and low-rigidity supporting means disposed in series with the high-rigidity displacement
producing means and having a low attenuation factor.
In this embodiment, as shown in FIG. 1, a first driving mechanism comprises (i) a coiled spring (low-rigidity supporting means) 550.sub.1 having an end connected to the supporting reference plate 530 through a spring mounting member 531.sub.1,
provided on the supporting reference plate 530 in a front and righthand side portion, as viewed in the drawing, adjacent to the vacuum chamber 510 and (ii) a hydraulic cylinder (high-rigidity displacement producing means) 540.sub.1 which is coupled in
series to the other end of the coiled spring 550.sub.1 through a rod 543.sub.1 and is fixedly provided on the top plate of the main frame 511.
A second driving mechanism comprises (i) a coiled spring (low-rigidity supporting means) 550.sub.2 having an end connected to the supporting reference plate 530 through a spring mounting member 531.sub.2, provided on the supporting reference
plate 530 in a front and left-hand side portion, as viewed in the drawing, adjacent to the vacuum cheer 510 and (ii) a hydraulic cylinder (high-rigidity displacement producing means) 540.sub.2 which is coupled in series to the other end of the coiled
spring 550.sub.2 through a rod 543.sub.2 and is fixedly provided on the top plate of the main frame 511.
A third driving mechanism comprises (i) a coiled spring (low-rigidity supporting means) 550.sub.3 having an end connected to the supporting reference plate 530 through a spring mounting member 531.sub.3 (FIG. 3), provided on the supporting
reference plate 530 in a middle and rear side portion, as viewed in the drawing, adjacent to the vacuum chamber 510 and (ii) a hydraulic cylinder (high-rigidity displacement producing means) 540.sub.3 which is coupled in series to the other end of the
coiled spring 550.sub.3 through a rod 543.sub.3 and is fixedly provided on the top plate of the main frame 511.
(d) Displacement Detecting Means:
The displacement detecting means serves to detect the amount of displacement of each of the respective high-rigidity displacement producing means of the three sets of driving mechanisms.
In this embodiment, as the displacement detecting means, there are provided a displacement detecting sensor 541.sub.1 for detecting the amount of displacement of the rod 543.sub.1 of the hydraulic cylinder 540.sub.1, a displacement detecting
sensor 541.sub.2 for detecting the amount of displacement of the rod 543.sub.2 of the hydraulic cylinder 540.sub.2, and a displacement detecting sensor 541.sub.3 for detecting the amount of displacement of the rod 543.sub.3 of the hydraulic cylinder
540.sub.3.
Here, the displacement sensor 541.sub.1 has a free end which is urged downwardly so that normally it contacts the upper surface of a displacement detecting reference plate 542.sub.1 mounted to the rod 543.sub.1 of the hydraulic cylinder
540.sub.1, and thus it detects the amount of displacement of the rod 543.sub.1 in the Y-axis axis direction (direction of height) illustrated. In a similar manner, the remaining two displacement sensors 541.sub.2 and 541.sub.3 detect the amount of
displacement of the rod 543.sub.2 of the hydraulic cylinder 540.sub.2 and that of the rod 543.sub.3 of the hydraulic cylinder 540.sub.3, respectively.
(e) Control Mechanism:
The control mechanism includes supporting force predicting means for predicting the supporting force of each of the coiled springs 550.sub.1 -550.sub.3 of the three sets of driving mechanisms, corresponding to the gravity center positions of the
stage 520 and the Y-axis stage 522, respectively.
The attitude control device of this embodiment includes, as the supporting force predicting means, (i) three distortion gauges (not shown) attached to the coiled springs 550.sub.1 -550.sub.3, respectively, (it) measuring means for detecting the
position of the gravity center .alpha. of the stage 520 as well as the position of the gravity center .beta. of the Y-axis stage 522, and (iii) a central processing unit (CPU), not shown, for determining the supporting forces. The measuring means
comprises a laser interferometer (not shown) of known type, and the gravity center position can be detected from the positional relationship of the stage 520 with respect to the stage frame 526 which can be measured by the laser interferometer by
projecting a laser beam to an L-shaped movable mirror 591 (FIG. 2), provided on the stage 520, and two fixed mirrors 590.sub.1 and 590.sub.2 (FIG. 2) provided on the stage frame 526.
The operation of the attitude control device of this embodiment will be explained.
Prior to moving the stage 520 and the Y-axis stage 522, the CPU predicts the amount of the displacement of the stage 520 and that of the Y-axis stage 522. Then, in accordance with the results of the prediction, it supplies driving signals to the
hydraulic cylinders 540.sub.1 -5450.sub.3, respectively, in accordance with the results of the prediction, by which the supporting reference plate 530 is so controlled that it is held continuously parallel to the floor and by which the attitude of the
stage frame 526 is held unchanged. Here, these amounts of movements are stored in a memory (not shown) beforehand and, as required, the CPU reads these amounts out of the memory and produces driving signals through computations such as follows:
Now, a case wherein the stage 520 is moved by the X-axis driving device 524.sub.1 by .DELTA.X and is moved by the Y-axis driving device 524.sub.2 by .DELTA.Y (the Y-axis stage is moved by .DELTA.Y, too), is considered.
Here, component forces are defined as below.
(a) Component Forces P1o, P2o and P3o and Component Forces P1, P2 and P3:
These component forces are those which are to be produced in the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting reference plate 530 by the three coiled springs 550.sub.1 -550.sub.3, in order to hold the attitude of
the stage frame 526. Here, the component forces P1o-P3o are those prior to the movement of the stage 520; whereas the component forces P1m-P3m are those after the movement of the stage 520.
(b) Component Forces P1mo, P2mo and P3mo and Component Forces P1m, P2m and P3m:
These component forces are those of the gravity of the stage 520 as applied to the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting reference plate 530. Here, the component forces P1mo-P3mo are those prior to the
movement of the stage 520: whereas the component forces P1m-P3m are those after the movement of the stage 520.
(c) Component Forces P1no, P2no and P3no and Component Forces P1n, P2n and P3n:
These component forces are those of the gravity of the Y-axis stage 522 as applied to the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting reference plate 530. Here, the component forces P1no-P3no are those prior to
the movement of the stage 520; whereas the component forces P1n-P3n are those after the movement of the stage 520.
(d) Component Forces P1co, P2co and P3co and Component Forces P1c, P2c and P3c:
These component forces are those of the gravity of elements (such as the vacuum chamber 510) other than the stage 520 and the Y-axis stage 522, as applied to the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting
reference plate 530. Here, the component forces P1co-P3co are those prior to the movement of the stage 520; whereas the component forces P1c-P3c are those after the movement of the stage 520.
Now, those other than the stage 520 and the Y-axis stage 522 do not move, and the component forces P1co-P3co as well as the component forces P1c-P3c are known and unchangeable. Therefore, the attitude of the stage frame 526 can be held, after
movement of the stage 520, by applying forces P1, P2 and P3 as represented by the following equations to the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting reference plate by using the coiled springs 550.sub.1 -550.sub.3,
respectively:
Since the component forces P1o, P2o and P3o can be detected through the distortion gauges attached to the coiled springs 550.sub.1 -550.sub.3, respectively, the forces P1mo+P1no, P2mo+P2no and P3mo+P3no in the right sides of equations (7)-(9) can
be determined in accordance with the following equations:
Also, the forces P1m+P1n, P2m+P2n and P3m+P3n in the right sides of equations (7)-(9) can be determined in the following manner:
As described, since the attitude control device of this embodiment is equipped with measuring means, it is possible to determine the coordinates S.sub.1 -S.sub.3 of the gravity center .alpha. of the stage 520, when the spring mounting members
531.sub.1 -531.sub.3 of the supporting reference plate 530 are taken as origins, as well as the coordinates SY.sub.1 -SY.sub.3 of the gravity center .alpha. of the Y-axis stage 522.
Assuming now that the stage 520 and the Y-axis stage 522 are at those positions as shown in FIG. 3, the coordinates S.sub.1 -S.sub.3 and SY.sub.1 -SY.sub.3 can be expressed as follows:
S.sub.1 (X1mo, Y1mo, Z1mo)
S.sub.2 (X2mo, Y2mo, Z2mo)
S.sub.3 (X3mo, Y3mo, Z3mo)
SY.sub.1 (X1no, Y1no, Z1no)
SY.sub.2 (X2no, Y2no, Z2no)
SY.sub.3 (X3no, Y3no, Z3no)
Here, if the mass of the stage 520 is Mm and the mass of the Y-axis stage is Mn, then equations regarding the balance of gravity and the balance of moment about the gravity center, of the stage 520 after movement, as well as equations regarding
the balance of gravity and the balance of moment about the gravity center, of the Y-axis stage 522 after movement, are such as follows:
From equations (13)-(18) and by using .DELTA.X as a function, the component forces P1m-P3m and P1n-P3n can be determined. Therefore, it is possible to determine the forces P1m+P1n, P2m+P2n and P3m+P3n in the right sides of equations (7)-(9).
It is to be noted here that the forces P1-P3 as represented by equations (7)-(9) can be applied to the spring mounting members 531.sub.1 -531.sub.3, respectively, of the supporting reference plate 530 with the coiled springs 550.sub.1 -550.sub.3,
respectively, by applying to the coiled springs 550.sub.1 -550.sub.3 such displacements .DELTA.L.sub.1 -.DELTA.L.sub.3 as expressed by the following equations:
wherein K is the constant of each of the springs 550.sub.1 -550.sub.3.
The above-described computations are all carried out in the CPU, and the CPU supplies those driving signals to the hydraulic cylinders 540.sub.1 -540.sub.3 by which the displacements .DELTA.L.sub.1 -.DELTA.L.sub.3 as determined by equations
(19)-(21) are applied to the coiled springs 550.sub.1 -550.sub.3, respectively. After supplying the driving signals, the CPU receives an output signal from supporting reference plate displacement detecting sensors 532 and finally checks the attitude of
the stage frame 526 (subject of control) after execution of the control.
It is to be noted that, in regard to the actuation of the hydraulic cylinders 540.sub.1 -540.sub.3, a closed loop control system is provided, for stabilized control, wherein the driving signals as well as the output signals of the displacement
sensors 541.sub.1 -541.sub.3 are inputted to servo circuits (not shown) provided in relation to the hydraulic cylinders 540.sub.1 -540.sub.3.
However, in place of the hydraulic cylinders 540.sub.1 -540.sub.3, as an example, a combination of a ball screw mechanism and a pulse motor of known type may be used and an open loop control system may be provided wherein the ball screw mechanism
is driven by the pulse motor to apply displacement to the coiled spring 550.sub.1. On that occasion, use of the displacement sensors 541.sub.1 -541.sub.3 is not necessary.
Further, while each of the displacements .DELTA.L.sub.1 -.DELTA.L.sub.3 corresponding to the amount of movement (.DELTA.X, .DELTA.Y, .DELTA.Z) to a target position of the stage 520 may be applied at once, as an alternative, those displacements
.DELTA.L.sub.1 (t)-.DELTA.L.sub.3 (t) corresponding to the movement amount (.DELTA.X(t), .DELTA.Y(t), .DELTA.Z(t)) of the stage 520 for each regular time period t may be stored in the memory and the hydraulic cylinders 540.sub.1 -540.sub.3 may be
actuated at regular intervals t.
FIG. 4 is a schematic view of an attitude control device according to a second embodiment of the present invention.
This attitude control device differs from the FIG. 1 device in that the former comprises a subsidiary frame 12 provided between a main frame 11 and a vacuum chamber 10 as well as four linear motors each being provided between a top or side plate
of the subsidiary frame 12 and the vacuum chamber 10 or between the floor and the vacuum chamber 10 and in that a CPU 70 shown in FIG. 8 includes canceling force predicting means (to be described later).
More specifically, as compared with the attitude control device of FIG. 1 by which the attitude of the stage frame 526 can be held against a static force as the stage 520 or the Y-axis stage 522 moves, the attitude control device of this
embodiment is operable to hold the attitude of the stage frame 26 against a dynamic force, in addition to a static force, as a stage 20 or a Y-axis stage 22 (FIG. 5) moves.
The function of this attitude control device for holding the attitude of the stage frame 26 against a static force, is substantially the same as that of the FIG. 1 device. Therefore, description will now be made of the function of holding the
attitude of the stage frame 26 against a dynamic force, through cooperation of the four linear motors 60.sub.1 -60.sub.4 and the canceling force predicting means.
The linear motors 60.sub.1 -60.sub.4 serve as four sets of thrust producing mechanisms for producing thrusts in parallel to coiled springs (low-rigidity supporting means) 50.sub.1 -50.sub.3, each mechanism comprising a first fixed member 62.sub.1
(FIG. 6C) which is fixedly secured to the subsidiary frame (a frame having high rigidity) 12, and a movable member 66.sub.1 (FIG. 6B) which is provided out of contact with the first fixed member 62.sub.1 and is fixed to the stage frame (member to be
supported) 26.
Since the linear motors 60.sub.1 -60.sub.4 have the same structure, one (60.sub.1) of them will be explained here.
As shown in FIGS. 6A-6C, the linear motor 60.sub.1 comprises constituent elements such as described below.
(a) First Fixed Member 62.sub.1 :
The first fixed member 62.sub.1 is shown in FIG. 6C, and the linear motor 60.sub.1 is fixedly mounted on a surface at the right-hand side of the subsidiary frame 12 as viewed in FIG. 4. Also, it is made of a ferromagnetic material, to provide a
yoke.
(b) Second Fixed Member 61.sub.1 :
The second fixed member 61.sub.1 is shown in FIG. 6A and it has a channel-like shape, having a wall opposed to the first fixed member 62.sub.1 and two side walls (see FIG. 7A) an end of each of which is fixed to an end of the top surface of the
fixed member 62.sub.1. Also, it is made of a ferromagnetic material, to provide a yoke.
(c) Two Permanent Magnets 63.sub.1 and 64.sub.1 :
These two permanent magnets 63.sub.1 and 64.sub.1 are mounted along a longitudinal center line of a surface of the second fixed member 61.sub.1 as opposed to the first fixed member 62.sub.1. Here, as shown in FIG. 6A, the permanent magnet
63.sub.1 mounted to a portion at the left-hand side of the opposed surface of the second fixed member 61.sub.1, has an N-pole 63.sub.1N at a front side thereof and an S-pole 63.sub.1S at a rear side thereof, as viewed in the drawing. Also, the permanent
magnet 64.sub.1 mounted to a portion at the right-hand side of the opposed surface of the second fixed member 61.sub.1, has an N-pole 64.sub.1N at a left-hand side and an S-pole 64.sub.1S at a right-hand side, as viewed in the drawing.
(d) Movable Member 66.sub.1 :
As shown in FIG. 6B, the movable member 66.sub.1 has a channel-like shape and is made of a material having a large electric resistance, for preventing production of an induced current. Also, two coils 67.sub.11 and 67.sub.12 are embedded within
the bottom of the movable member 66.sub.1, wherein straight portions of them are placed with mutual deviation of 90 deg. at those positions opposed to the N-pole 63.sub.1N and the S-pole 63.sub.1S of the permanent magnet 63.sub.1 and to the N-pole
64.sub.1N and the S-pole 64.sub.1S of the permanent magnet 64.sub.1 (see FIG. 7B).
As shown in FIG. 8, the coils 67.sub.11 and 67.sub.12 of the linear motor 60.sub.1 are connected to a CPU 70 through current amplifiers 80.sub.11 and 80.sub.12, respectively, and they are driven by this CPU 70.
Further, as shown in FIG. 7A, the movable member 66.sub.1 has its bottom surface 66.sub.11 sandwiched in a non-contact state between the second fixed member 61.sub.1 and the first fixed member 62.sub.1.
Referring now to FIG. 5, the manner of fixing the linear motors 60.sub.1 -60.sub.4 to the stage frame 26 will be explained.
For the fixation of the linear motor 60.sub.1 to the right-hand side of the stage frame 26, as viewed in the drawing, four linear motor mounting members are used (only two 27.sub.1 and 27.sub.2 of them are illustrated).
Here, each of the two mounting members 27.sub.1 and 27.sub.2 has an end fixed to the front side of the movable member 66.sub.1, as viewed in the drawing, and another end fixed to the right-hand side of the stage frame 26 as viewed in the drawing. Also, these mounting members are loosely fitted into two bores, respectively, formed in the right-hand side of the vacuum chamber 10 as viewed in the drawing. The unshown two linear motor mounting members each has an end fixed to the rear side of the
movable member, as viewed in the drawing, and another end fixed to the right-hand side of the stage frame 26 as viewed in the drawing. These unshown mounting members are loosely fitted into two bores, respectively, formed in the right-hand side of the
vacuum chamber at positions rearwardly of the aforementioned two bores, as viewed in the drawing.
Mounted to the outside portions of these four bores are bellows (only two 28.sub.1 and 28.sub.2 of them are shown) which serve to tightly close the vacuum chamber 10 and also to prevent transmission of any deformation thereof to the stage frame
26.
The fixation of the linear motor 60.sub.2 to the left-hand side of the stage frame 26 as viewed in the drawing and the fixation of the linear motor 60.sub.3 to the top of the stage frame 26, are made in a similar manner as described.
The fixation of the linear motor 60.sub.4 to the bottom of the stage frame 26 is made through four linear motor mounting members (only two 27.sub.7 and 27.sub.8 of them are shown) inserted into four bores formed in the supporting reference plate
30. However, no bellows is mounted to the outside of each bore, such that displacement of the supporting reference plate 30 causes displacement of the stage frame 26, through the motor mounting members.
The control mechanism of this attitude control device is similar to that shown in FIG. 1 in that it comprises: three distortion gauges (supporting force predicting means), not shown, attached to the coiled springs 50.sub.1 -50.sub.3 of the three
sets of driving mechanisms, respectively, for predicting the supporting forces of the coiled springs 50.sub.1 -50.sub.3, respectively, corresponding to the gravity center positions of the stage 20 and the Y-axis stage 22; measuring means for detecting
the position of the gravity center .alpha. of the stage 20 as well as the position of the gravity center .beta. of the Y-axis stage 22; and a CPU 70 (see FIG. 8) for determining the supporting forces. However, it differs from the control mechanism of
the attitude control device of FIG. 1 in that the CPU 70 includes canceling force predicting means for predicting, when the movable member (i.e. the stage 20 or the Y-axis stage 22) is accelerated, such force that the reaction force or reaction moment
received by the supported member (i.e. the stage frame 26) is canceled by the thrust producing mechanisms (i.e. the linear motors 60.sub.1 -60.sub.4).
The operation of this attitude control device will now be explained.
The static force balancing when the stage 20 and the Y-axis stage 22 move is attainable in a similar manner as in the attitude control device of FIG. 1 and, therefore, it is not explained here. Only the dynamic force balancing as the stage 20
and the Y-axis stage 22 move, will now be explained.
The following distances can be measured with the above-described measuring means (see FIG. 9).
(a) Distance X.sub.M1 : The distance from the gravity center .alpha. of the stage 20 to the center of the movable member 66.sub.1 along the X axis illustrated. It changes with the movement of the stage 20.
(b) Distance X.sub.M2 : The distance from the gravity center .alpha. of the stage 320 to the center of the movable member 66.sub.2 along the X axis illustrated. It changes with the movement of the stage 20.
(c) Distance X.sub.N1 : The distance from the gravity center .beta. of the Y-axis stage 22 to the center of the movable member 66.sub.1 along the X axis illustrated. It does not change with the movement of the stage 20.
(d) Distance X.sub.N2 : The distance from the gravity center .beta. of the Y-axis stage 22 to the center of the movable member 66.sub.2 along the X axis illustrated. It does not change with the movement of the stage 20.
(e) Distance Y.sub.M1 : The distance from the gravity center .alpha. of the stage 20 to the center of the movable member 66.sub.3 along the Y axis illustrated. It changes with the movement of the stage 20.
(f) Distance Y.sub.M2 : The distance from the gravity center .alpha. of the stage 20 to the center of the movable member 66.sub.4 along the Y axis illustrated. It changes with the movement of the stage 20.
(g) Distance X.sub.MN : The distance from the gravity center .alpha. of the stage 20 to the gravity center .beta. of the Y-axis stage 22 along the X axis illustrated. It changes only when the stage 20 moves in the X-axis direction illustrated.
First, the balance of force F.sub.X applied to the stage 20 as it is moved in the X-axis direction illustrated by means of the X-axis driving device 24.sub.1, is considered.
The reaction force and reaction moment resulting from the force F.sub.X can be canceled by producing thrusts F.sub.U and F.sub.D, to be expressed below, and this can be attained by applying drive currents to a coil 67.sub.32 of the linear motor
60.sub.3 fixedly provided on the top of the stage frame 26 (FIG. 8) and to a coil 67.sub.42 of the linear motor 60.sub.4 fixedly provided on the bottom of the stage frame 26.
Next, the balance of force F.sub.Y applied to the stage 20 and the Y-axis stage 22 as the latter is moved in the Y-axis direction illustrated by means of the Y-axis driving device 24.sub.2, is considered.
Here, the acceleration a.sub.Y of the stage 20 and the Y-axis stage 22 is:
and clockwise reaction moment Mm.multidot.a.sub.Y, in the drawing, is applied to the Y-axis stage 22 from the stage 20.
The reaction force and the reaction moment resulting from the force F.sub.Y can be canceled by producing thrusts F.sub.L and F.sub.R, to be expressed below, and this can be attained by applying drive currents to a coil 67.sub.11 of the linear
motor 60.sub.1 fixedly provided on the right-hand side of the stage frame (FIG. 8) and to a coil 67.sub.21 of the linear motor 60.sub.2 fixedly provided on the left-hand side of the stage frame 26.
Since in an exposure apparatus the amount of movement of each of the stage 20 and the Y-axis stage 22 is predetermined, these amounts may be stored into a memory (not shown) beforehand and the CPU 70 in FIG. 8 may read the amount of movement at
that moment out of the memory and execute the computations according to equations (22)-(26) to determine the thrusts F.sub.U, F.sub.D, F.sub.L and F.sub.R. Then, by applying corresponding drive currents to the coils 67.sub.32, 67.sub.42, 67.sub.11 and
67.sub.21 through the current amplifiers 80.sub.32, 80.sub.42, 80.sub.11 and 80.sub.21, respectively, it is possible to hold the attitude of the stage frame 26 against the dynamic force.
Here, as the amount of movement for each of the stage 29 and the Y-axis stage 22, the distances to the target positions of them may be stored into the memory. Alternatively, however, the amount of movement at each time moment may be memorized
and those thrusts F.sub.U (t), F.sub.D (t), F.sub.L (t) and F.sub.R (t) at each time moment may be determined by the CPU 70 in a similar manner, to thereby hold the attitude of the stage frame 26 against the dynamic force.
FIG. 10 is a schematic view of an attitude control device according to a third embodiment of the present invention, and shows the connection to a CPU of coils of linear motors of an attitude control device in an X-ray exposure apparatus.
This attitude control device differs from that shown in FIG. 4 in that it is equipped with four sets of damping force producing mechanisms each comprising a fixed member and a movable member disposed out of contact with the fixed member and
fixedly provided on a member to be supported, the mechanisms providing damping forces in directions of six axes, to the member to be supported.
More specifically, in this attitude control device, the coils 67.sub.11, 67.sub.12, 67.sub.21, 67.sub.22, 67.sub.31, 67.sub.32, 67.sub.41 and | | |
