Anti-vibration apparatus and anti-vibration method thereof

Details Anti-vibration apparatus and anti-vibration method thereof Anti-vibration apparatus and anti-vibration method thereof

1998-03-06

2001-01-09

Butler, Douglas C. (Department: 3613)

Brakes

Inertia of damping mass dissipates motion

C267S136000, C248S550000

Reexamination Certificate

active

06170622

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an active anti-vibration apparatus, such as for example, an air spring type active anti-vibration apparatus which employs air spring actuators and which is ideally used as a component unit of a semiconductor exposure apparatus with an exposure XY stage mounted thereon.
A group of equipment such as an optical microscope and an exposure XY stage which are susceptible to vibration is mounted on an anti-vibration table. The exposure XY stage, in particular, must be mounted on an anti-vibration table which is able to eliminate vibration transmitted from outside as much as possible in order to permit proper and quick exposure because exposure has to be carried out with the exposure XY stage completely stopped and still. The exposure XY stage has an operation mode in which the exposure XY stage performs intermittent movement known as “step-and-repeat”. In this step-and-repeat mode, the stage itself repeatedly generates stepping vibration; therefore, considerations should be given to the vibration of the anti-vibration table caused by the foregoing stepping vibration.
If the vibration cannot be completely settled and if it remains, then exposure operation cannot be initiated. For this reason, the anti-vibration table is required to provide vibration controlling performance for eliminating external vibration and the vibration attributable to the motion of mounted equipment in a well balanced manner.
In recent years, a scan-type semiconductor exposure apparatus which irradiates exposure light to a silicon wafer while scanning an XY stage or the like is beginning to replace the step-and-repeat type semiconductor exposure apparatus which brings the XY stage to a complete halt, then irradiates exposure light to the silicon wafer mounted on the stage. The anti-vibration table used for such a scan-type apparatus is also required to provide controlling performance for eliminating external vibration and to control the vibration resulting from the motion of mounted equipment in a well-balanced manner.
As it is widely known, the anti-vibration tables are classified into passive type and active type. Recently, there has been a trend toward using active anti-vibration apparatuses to respond to the demand for highly accurate positioning, highly accurate scanning, quicker movement, etc., required of the equipment mounted on an anti-vibration table. Air springs, voice coil motors, piezo elements, etc., are known as the actuators employed for such anti-vibration apparatuses. A specific description will be given herein of an active anti-vibration apparatus as a conventional example using air springs as the actuators.
First, referring to
FIG. 11
, the configuration and operation of the active anti-vibration apparatus of the prior art, which employs air springs as the actuators, will be described. In
FIG. 11
, an anti-vibration table
1
on which precision equipment is mounted has active support legs
2
a
through
2
d.
The active support legs
2
a
through
2
d
are primarily composed of air spring actuators which include vibration measurers
3
a
through
3
d
for measuring the vibration in the horizontal direction, air spring actuators
4
a
through
4
d
which include servo valves (not shown) for generating drive power in the horizontal direction, and displacement sensors
6
a
through
6
d
for measuring horizontal displacement. Acceleration sensors, geophone sensors, etc., may be used as the vibration measurers
3
a
through
3
d
. As the displacement sensors
6
a
through
6
d
, eddy current type displacement sensors, capacitive sensors, position sensors employing photoelectric converters, etc., may be used.
As shown in the drawing, the active support legs
2
a
through
2
d
which include, as primary composing elements thereof, the foregoing air spring actuators
4
a
through
4
d
, the displacement sensors
6
a
through
6
d
, and vibration measurers
3
a
through
3
d
, are disposed at the four corners of the anti-vibration table
1
to support the anti-vibration table
1
and the precision equipment mounted thereon. Although the main composing elements which perpendicularly support the anti-vibration table
1
are not shown, they share the same configuration as the aforesaid composing elements which horizontally support the anti-vibration table.
The configuration and operation of a decoupling feedback apparatus in each motional mode for the active support legs
2
a
through
2
d
of the control scheme of the active anti-vibration apparatus will now be described.
First, electrical output signals Aa through Ad of the vibration measurers
3
a
through
3
d
of an acceleration sensor or the like are supplied to a motional-mode selector
7
A related to the acceleration for selecting the translation in the x-direction, the translation in the y-direction, and the rotation about the z-axis of the anti-vibration table
1
. Based on the received electrical output signals, the motional-mode selector
7
A issues motional mode acceleration signals (a
x
, a
y
, and a&thgr;z) which are turned into negative feedback signals related to the acceleration for each motional mode via gain compensators
17
x
,
17
y
, and
17
z
which have appropriate amplification degrees and time constants; the negative feedback signals are sent back to the section preceding a motional-mode distributor
9
. This acceleration feedback loop provides a damping operation for each motional mode to stabilize the operation of the anti-vibration table
1
.
The electrical output signals Za through Zd of the displacement sensors
6
a
through
6
d
are supplied to error amplifiers
10
a
through
10
d
. Another type of inputs is supplied to the respective error amplifiers
10
a
through
10
d
from a position target voltage input terminal
11
. The voltage applied to the input terminal represents the equilibrium position of the anti-vibration table
1
with respect to the foundation such as a floor on which the active support legs
2
a
through
2
d
are installed. Position error signals e
a
through e
d
which are the outputs of the error amplifiers
10
a
through
10
d
are applied to a motional-mode selector
7
P so that the motional-mode selector
7
P related to displacement issues motional mode error signals (s
x
, s
y
, and s&thgr;z) which are then applied to PI compensators
12
x
,
12
y
, and
12
&thgr;
z
for setting the steady-state error to zero for each motional mode, thus making up a positional feedback loop. In this case, P denotes proportion and I denotes integrating operation.
Next, the output signals of the PI compensators
12
x
,
12
y
, and
12
&thgr;
z
and the negative feedback signals related to the acceleration by motional mode which are issued from the gain compensators
17
x
,
17
y
, and
17
z
are added to provide drive signals (d
x
, d
y
, and d&thgr;z). The drive signals (d
x
, d
y
, and d&thgr;z) by motional mode are applied to the motional-mode distributor
9
which generates drive signals to be sent to the respective axes. When the output signals (d
a
, d
b
, d
c
, and d
d
) of the motional-mode distributor
9
are supplied to voltage-current converters
8
a
through
8
d
of the respective axes, the servo valves (not shown) are opened or closed to regulate the internal pressures of the air spring actuators
4
a
through
4
d
; the changes in the internal pressures cause the applied voltage supplied from the position target voltage input terminal
11
to maintain the anti-vibration table
1
at a predetermined position without a steady-state error.
FIG. 12
is a top plan view showing the layout of the active support legs
2
a
through
2
d
related to the anti-vibration apparatus shown in FIG.
11
. The twin-headed arrows entered in the respective support legs in the drawing indicate the directions in which the air spring actuators
4
a
through
4
d
can be driven and they also indicate the measurement directions of the vibration measurers
3
a
through
3
d
and the displacement sensors
6
a
through
6
d
. It can be easily understood that pro

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