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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stage device, and more particularly to a
stage device adapted for use in an exposure apparatus for manufacturing a
semiconductor device, a substrate for a liquid crystal display device, a
thin film magnetic head or the like.
2. Related Background Art
In a lithographic process for producing a semiconductor device, substrate
for a liquid crystal display device or the like, there is employed a
projection exposure apparatus for exposing a photosensitive substrate to
the image of a pattern of a photomask or a reticle (hereinafter
collectively called reticle) through a projection optical system. Such
apparatus is usually provided with a stage device capable of supporting
the photosensitive substrate (wafer) and of two-dimensional movement, and
the exposure is executed by aligning the reticle and the wafer, through
positioning of the stage device to a predetermined position.
Such projection exposure apparatus is placed on an antivibration table, in
order to prevent undesirable effect for example on the precision of
alignment between the reticle and the wafer, resulting from the vibration
of the ground (exterior of the apparatus). Such antivibration table
attenuates the vibration from the exterior of the apparatus, by means of
an elastic member or a damping member.
FIG. 4 is a schematic view of a conventional projection exposure apparatus.
In the stage device employed in the conventional projection exposure
apparatus for semiconductor device production, as shown in FIG. 4, a stage
control unit (not shown) drives a motor 4Y provided on an antivibration
table 12 constituting a base plate, thereby driving a table 1 to a
predetermined position through a feed screw (driving shaft) 3Y. The table
1 supports thereon a wafer W constituting the photosensitive substrate.
Onto a desired exposure area on the wafer, light emitted from a light
source 20 and directed onto a reticle 18 through an illumination optical
system 19, consisting of lens systems such as a fly's eye lens, a
condenser lens etc., is projected onto a wafer N by a projection lens 17,
whereby a mask pattern is imaged on the wafer. After a projection exposure
to the exposure area, the table 1 is suitably moved in such a manner that
a next exposure area is positioned in a predetermined position within the
projection field of the projection lens 17. An interferometer 7Y measures
the position of the table 1, based on the reflected light from a mirror 8Y
provided on the table 1.
In such stage device of the conventional configuration, the entire device
excluding the table 1 is fixed, as a rigid member, on the antivibration
table 12, and the table 1 is fixed, by means of the feed screw 3Y and a
guide mechanism (not shown) of the table 1, as a substantially rigid
member, to the main body of the device. Stated differently, the table 1
and the device are macroscopically integral, but, in consideration of the
comparison of the rigidity of the entire device and the supporting
rigidity of the table 1, they are microscopically equivalent to a
structural model in which the table is elastically supported on the base
plate. This is because, in the requested precision, the feed screw 3Y
cannot be regarded as a completely rigid body due to the play and friction
in the junction. Because of this fact, the driving (including deceleration
and stopping) of the table 1 generates vibration in the entire device
excluding the table 1. More specifically, the reaction force of the
driving force acting on the table 1 acts on the antivibration table,
thereby generating vibration in the entire device excluding the table 1.
However, the table 1 alone tends to remain in the original position by
inertia, so that so-called vibration-induced positional aberration is
generated between the entire device and the table 1, or between the
antivibration table 12 constituting the base plate and the table 1.
In such conventional stage device employed in the projection exposure
apparatus for producing semiconductor devices, in driving the table for
movement to a predetermined position, there is generated vibration in the
entire device, and a positional aberration is generated, resulting from
said vibration, between the antivibration table and the table. Since the
optical system for projection exposure and the reticle 18 are fixed as
rigid members to the base plate as explained before, the positional
aberration between the reticle 18 (or the projection optical system 17)
and the wafer placed on the table 1 detrimentally affects the performance
of the exposure apparatus. For this reason the projection exposure has to
be executed after the vibration becomes sufficiently small by spontaneous
attenuation, so that the throughput is significantly lowered.
SUMMARY OF THE INVENTION
The present invention, attained in consideration of the foregoing, is
intended to provide a stage device not inducing the positional aberration
between the table and the base plate even if vibration is generated by the
driving of the table, and thus capable of improving the throughput.
The above-mentioned object can be attained, according to the present
invention, by a stage device comprising a base plate supported by an
antivibration device, a table supported slidably by said base plate, a
driving shaft connected to said table and adapted to cause a sliding
motion of said table, first drive means for driving said table through
said driving shaft for placing said table on a predetermined position on
said base plate, and second drive means.
Said second drive means is adapted to provide said table with a force in
such a manner as to correct the relative positional aberration between
said base plate and said table, resulting from the vibration of said base
plate induced by the reaction force of the driving for said table.
In a preferred embodiment of the present invention, the second drive means
is composed of a linear motor mechanism provided between the base plate
and the table. More preferably there is further comprised acceleration
measuring means for measuring the acceleration of the base plate, or
acceleration calculating means for numerically calculating the
acceleration of the base plate, based on the given acceleration of the
table, or acceleration measuring means for measuring the acceleration of
the table and acceleration calculating means for numerically calculating
the acceleration of the base plate based on the measured acceleration of
the table.
The present inventor has observed the positional aberration between the
antivibration table and the driven table resulting from the vibration,
induced by the reaction force of the driving of the table, and has
achieved the present invention for correcting and resolving said
positional aberration, by causing the driven table to follow the vibrating
motion of the base plate, namely providing the driven table with an
acceleration the same as that of the base plate on real-time basis.
More specifically, according to the present invention, by providing the
driven table with a force F(t) given by the following equation on
real-time basis:
F(t)=m.times.a(t)
wherein a(t) is the acceleration of the base plate at a time t during the
table movement, and m is the mass of the table, the relative speed between
the base plate and the table becomes zero at the end of the table
movement, and said positional aberration resulting from the vibration can
be resolved.
The acceleration a(t) of the base plate can be easily measured, for example
by an acceleration sensor mounted thereon. Consequently, the force F(t),
obtained by multiplying the acceleration a(t) of the base plate measured
on real-time basis with the already known mass of the table, is applied to
the table by suitable means such as a linear motor mounted between the
table and the base plate, thereby forcedly providing the table with an
acceleration the same as that a(t) of the base plate and causing the table
to completely follow the vibration of the base plate.
In a DC linear motor, the generated propulsion force F.sub.L is represented
by the product of a constant k specific to the linear motor and the
current i, namely F.sub.L =k.times.i. Therefore, a desired propulsive
force can be easily applied to the table, by suitable control of the
current i.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a projection exposure apparatus in which the
stage device embodying the present invention is applicable;
FIG. 2 is a perspective view of a stage device embodying the present
invention;
FIG. 3 is a schematic lateral view of said stage device embodying the
present invention; and
FIG. 4 is a schematic view of a conventional stage device employed in the
projection exposure apparatus for semiconductor device manufacture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now the present invention will be clarified in detail by preferred
embodiments, shown in the attached drawings.
FIG. 1 is a schematic view showing the structure of a projection exposure
apparatus in which the stage device embodying the present invention can be
applied.
The structure of the illustrated apparatus is similar to that of the
conventional apparatus shown in FIG. 4. For this reason, components
corresponding to those shown in FIG. 4 are represented by same reference
numbers. The illustrated apparatus is different from the conventional
apparatus principally in that a linear motor mechanism is provided between
the table 1 and the antivibration table 12 as second drive means for the
table 1, and that an acceleration meter is provided on the antivibration
table 12 for measuring the acceleration thereof, and, because of these
differences, the control system is made different.
An antivibration device 13 is provided to attenuate the vibration from the
exterior of the apparatus. A support member 14A is fixed to the
antivibration table 12 and supports the projection optical system 17,
while a support member 14B is fixed to the support member 14A and supports
the reticle 18.
FIG. 2 is a perspective view of a stage device embodying the present
invention. The illustrated device is composed of a combination of a stage
device movable in the X-direction and a stage device movable in the
Y-direction, whereby the table 1 is arbitrarily movable in the horizontal
plane.
The table 1 shown in FIG. 2 is composed of an X-table 1X movable in the
X-direction and a Y-table 1Y movable in the Y-direction, wherein said
X-table 1X is provided on the Y-table 1Y. The X-table 1X is supported by
the Y-table 1Y by means of a non-contact guide mechanism (such as an air
bearing) 2X extending in the X-direction, and the Y-table 1Y supporting
the X-table 1X, supporting the X-table 1X, is provided on the
antivibration table 12, and is supported thereby by means of a non-contact
guide mechanism 2Y (such as an air bearing) extending in the Y-direction.
The Y-table 1Y is driven in the Y-direction by a feed screw 3Y, provided
parallel to the guide mechanism 2Y and driven by a motor 4Y mounted on the
antivibration table 12. Between the Y-table 1Y and the antivibration table
12 there is provided a linear motor mechanism 5Y, 6Y of which details will
be given later. The X-table 1X is driven in the X-direction by a feed
screw 3X, provided parallel to the guide mechanism 2X and driven by a
motor 4X mounted on the Y-table 1Y. Between the X-table 1X and the Y-table
1Y there is provided a linear motor mechanism 5X, 6X of which details will
be given later.
A laser interferometer 7Y measures the position of the Y-table 1Y in
non-contact manner, based on the returning light from a mirror 8Y provided
on the X-table 1X, and is capable of highly precise detection of the
position of the Y-table 1Y. A laser interferometer 7X measures the
position of the X-table 1X in non-contact manner, based on the returning
light from a mirror 8X provided on the X-table 1X, and is capable of
highly precise detection of the position of the X-table 1X. Although not
illustrated in FIG. 2, the laser interferometer 7Y is fixed on the
antivibration table 12, while the laser interferometer 7X is fixed on the
Y-table 1Y. On the antivibration table 12, an acceleration meter 9Y is
provided for measuring the acceleration of the antivibration table 12 in
the Y-direction, while on the Y-table 1Y an acceleration meter 9X is
provided for measuring the acceleration of the Y-table 1Y in the
X-direction. The latter in fact measures the acceleration of the stage
device excluding the X-table 1X, thereby measuring the acceleration of the
antivibration table 12 in the X-direction. In the following text, the
acceleration measured by the acceleration meter 9X will be represented as
"acceleration of the Y-table 1Y in the X-direction".
Since the linear motor mechanism (5X, 6X) for driving the X-table 1X in the
X-direction and the linear motor mechanism (5Y, 6Y ) for driving the
Y-table 1Y in the Y-direction are the same in the basic structure, in the
following there will be only explained the former mechanism for driving
the X-table 1X in the X-direction, with reference to FIG. 3.
FIG. 3 is a schematic lateral view of the configuration of the stage device
embodying the present invention.
Between the X-table 1X and the Y-table 1Y there is provided the linear
motor mechanism (5X, 6X), composed of a stator 5X mounted on the Y-table
1Y and a movable member 6X mounted on a side, facing the Y-table 1Y, of
the X-table 1X.
Also in the Y-direction, a linear motor mechanism (5Y, 6Y) is similarly
provided between the Y-table 1Y and the antivibration table 12 (cf. FIG.
1).
The illustrated device is further provided with a controller 10, which
receives the table position information measured by the laser
interferometers 7X, 7Y in cooperation with the mirrors 8X, 8Y, and the
acceleration information measured by the acceleration meters 9X, 9Y, and
suitably drives the tables 1X, 1Y through the motors 4X, 4Y and the feed
screws 3X, 3Y or through the linear motor mechanisms (5X, 6X), (5Y, 6Y).
In addition, the controller 10 controls the entire device.
When the above-explained stage device of the present invention is employed
in the projection exposure apparatus for semiconductor device production,
the table 1 supporting the wafer constituting the photosensitive substrate
is driven, after a projection exposure, in such a manner that a next
exposure area is placed in a predetermined position within the projection
field of the projection optical system. More specifically, the controller
10 receives the current position information and the target position
information, and moves the tables 1X, 1Y rapidly to the target position by
means of the motors 4X, 4Y and the feed screws 3X, 3Y. In this operation,
each of the tables 1X, 1Y effects a motion under a positive acceleration,
a constant-speed motion and a motion under a negative acceleration. In the
following there will be explained the vibration and antivibration in the
X-direction.
The table 1X is subjected to an acceleration by the motor 4X and the feed
screw 3X, and a reaction force is applied to the Y-table 1Y on which said
motor 4X and feed screw 3X are mounted. As a result, the entire device
excluding the table 1X generates vibration. Since the table 1X is
supported on the Y-table 1Y by the non-contact guide mechanism 2X and the
feed screw 3X, the table 1X is subjected to inertia, thus tending to
remain in the original position, independently from the vibration of the
entire device.
This is because, though the table 1X generally moves integrally with the
entire device through the guide mechanism 2X and the feed screw 3X, it
does not completely follow the movement of the entire device as the feed
screw 3X etc. are not completely rigid.
Consequently, according to the present invention, the controller 10
receives the acceleration information of the Y-table 1Y in the
X-direction, measured by the acceleration meter 9X, and provides the table
1X a the real-time basis, with an acceleration same as said measured
acceleration of the Y-table 1Y in the X-direction, through the linear
motor mechanism 5X, 6X. As a result, during the movement of the X-table
1X, there is not generated the relative positional aberration between the
X-table 1X and the Y-table 1Y resulting from the vibration. Thus, since
the relative positional relationship is maintained between the reticle 18
and the wafer W, there can be executed the exposure operation without
awaiting the attenuation of the vibration of the device. The acceleration
meter 9X in this embodiment is provided on the Y-table 1Y, but it may
naturally be provided also on the antivibration table 12.
As already explained in the foregoing, since the acceleration a.sub.1 (t)
of the X-table 1X is measured on real-time basis by the acceleration meter
9X on the base plate and since the mass m.sub.1 of the X-table 1X is
already known, the X-table 1X is subjected to an acceleration the same as
that of the Y-table 1Y on real-time basis by the application of a force
F(t) =m.sub.1 .times.a.sub.1 (t). As a result, it is rendered possible to
cause the X-table 1X to completely follow the vibration of the Y-table 1Y
and thus to completely eliminate the aforementioned relative positional
aberration. The current i supplied to the linear motor mechanism (5X, 6X)
is suitably controlled by the controller 10 in such a manner that the
propulsive force F.sub.t generated by the linear motor mechanism (5X, 6X)
becomes always equal to the above-mentioned force F(t).
Also in the Y-direction, the acceleration information of the antivibration
table 12 is measured by the acceleration meter 9Y, and the controller 10
controls the linear motor mechanism (5Y, 6Y) in a similar manner as in the
X-direction. However, since the Y-table 1Y moves integrally with the
X-table 1X, the mass of the Y-table in this case is the sum of the mass
m.sub.1 of the X-table 1X and the mass m.sub.2 of the Y-table 1Y.
Consequently the force F(t) to be applied to the Y-table 1Y is given by:
F(t)=(m.sub.1 +m.sub.2).times.a.sub.2 (t),
wherein a.sub.2 (t) is the acceleration of the antivibration table 12.
In the foregoing embodiment, the acceleration of the antivibration table 12
is directly measured by the acceleration meter, and the table 1 is
forcedly subjected to the force determined from thus actually measured
acceleration. However, in consideration of the fact that the vibration of
the antivibration table 12 is induced by the driving of the table 1, the
acceleration of the antivibration table 12 can also be obtained by
numerical calculation, even without relying on the acceleration meter,
namely without direct measurement of the acceleration of the antivibration
table 12. Consequently the force to be applied to the table 1 can also be
determined by calculation.
With respect to the motion in the X-direction, the equation of motion of
the vibrating antivibration table 12, or the entire device excluding the
X-table 1X, can be represented as follows:
Fs(t)=M.multidot.x"(t)+B.multidot.x'(t)+K.multidot.x(t)
wherein
Fs: vibration inducing force applied to the antivibration table 12. Since
this force is the reaction force of the driving force applied to the
X-table 1X, Fs(t)=-m.sub.1 .times.a.sub.1 (t);
M: mass of the entire device excluding the X-table 1X;
x":acceleration of the antivibration table;
B: viscous resistance coefficient;
K: spring constant.
The mass M of the entire device excluding the table 1X, the viscous
resistance coefficient B, the spring constant K and the mass m.sub.1 of
the table are already known. Also the acceleration a.sub.1 (t) of the
table 1X is either already known as a design parameter, or can be
determined in the controller 10 from the position information of the table
measured by the aforementioned laser interferometer 7X. Thus it is
possible to determine the force Fs(t)=-m.sub.1 .times.a.sub.1 (t). Also
the spring constant K and the viscous resistance coefficient B are
parameters inherent to the antivibration pads supporting the antivibration
table 12 on the floor.
Thus the equation of motion of the antivibration table 12 can be solved by
a numerical calculation in a computer (controller 10), and the
acceleration x"(t) of the antivibration table can be calculated. The
operations of applying a predetermined force to the X-table 1X utilizing
the calculated acceleration x"(t) of the antivibration table thereby
completely eliminating the aforementioned relative positional aberration
are as already explained before. Also for the motion in the Y-direction,
the force to be applied to the Y-table 1Y can be determined by
calculation.
Also, if the acceleration a.sub.1 (t) of the table 1X is not known, the
present invention may utilize a speedometer instead of the laser
interferometer. Thus the controller 10 can determined the acceleration
a.sub.1 (t) from the output of such speedometer.
In the present embodiment, a linear motor mechanism is employed for
correcting the positional aberration between the table 1 and the
antivibration table, induced by vibration, but it may also be utilized as
vernier means for moving the table 1 by a small amount when the stopped
position of the table 1 does not match the target position, or as
deceleration means (damper) for accelerating the attenuation of the
vibration.
The present embodiment is a stage device adapted for use in a projection
exposure apparatus for semiconductor device production, but the present
invention is naturally applicable also to other general stage devices,
within the scope thereof.
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