Measuring and testing – Vibration – Vibrator
Reexamination Certificate
1999-10-26
2001-03-20
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Vibrator
C248S550000, C248S638000
Reexamination Certificate
active
06202492
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an anti-vibration apparatus and an exposure apparatus. More particularly, the present invention is suitably applied to an active type anti-vibration apparatus wherein an anti-vibration bed is driven by an actuator so that vibrations of the anti-vibration bed are suppressed. The present invention is also suitably applied to an exposure apparatus having the anti-vibration apparatus.
With the achievement of high accuracies of precision apparatus, such as step-and-repeat reduction projection type exposure apparatuses, i.e. steppers, there has occurred a need of controlling, on the micro-G level, microvibrations acting on a base plate (anti-vibration bed) from a floor where a stepper, or the like, is installed.
Various vibration-isolating pads are used to support an anti-vibration bed: For example, mechanical dampers having a compression coil spring placed in a damping fluid, and pneumatic dampers. The vibration-isolating pads per se, have a certain degree of centering function.
In particular, pneumatic spring type anti-vibration apparatuses having pneumatic dampers enable the spring constant to be set at a small value and are capable of suppressing vibrations of about 10 Hz or more. Therefore, this type of anti-vibration apparatus has widely been employed to support precision apparatus.
Recently, active type anti-vibration apparatuses have been proposed to move beyond the limitations of conventional passive type anti-vibration apparatuses. In the active type, vibrations of an anti-vibration bed are detected with a sensor, and an actuator is driven on the basis of the output of the sensor, thereby effecting vibration control. Thus, it is possible to provide an ideal vibration-isolating effect having no resonance peak in a low-frequency control band.
In an exposure apparatus, e.g. a stepper, an XY-stage (wafer stage), which is accelerated and decelerated to a considerable extent, is mounted on a base plate held by vibration-isolating pads. Therefore, the center of gravity of the exposure apparatus main body shifts at the same time as the XY-stage moves. When the center of gravity of the exposure apparatus main body has shifted in accordance with the stage movement, an active type anti-vibration apparatus provided in the exposure apparatus effects positioning of the XY-stage with respect to the initial position by a position control loop. As the amount of movement of the stage increases, the amount of change of the gravity center of the exposure apparatus main body also increases. Consequently, the base plate, on which the exposure apparatus main body is mounted, also inclines to a considerable extent. As the amount of change of the gravity center of the exposure apparatus main body increases, the amount of inclination of the base plate also increases, and the thrust required for the actuator to correct the inclination also increases.
In such an anti-vibration apparatus, a large amount of heat is generated from the actuator, and there is a large change in the temperature of an environment where the exposure apparatus is placed. The environmental temperature change affects the measuring accuracy of a laser interferometer that measures the position of the XY-stage, giving rise to a problem, such as degradation of the stage positioning accuracy.
To solve such a problem, it is conceivable to increase the gain of the position control loop of the anti-vibration apparatus. By doing so, the position control responsivity is improved, but the vibration-isolating performance is degraded because vibrations of the floor are transmitted to the exposure apparatus main body. Therefore, it is not an effective method. Accordingly, it is urgent to develop an apparatus capable of suppressing an environmental temperature change while ensuring the position control responsivity to a certain extent without degrading the vibration-isolating performance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an anti-vibration apparatus capable of efficiently suppressing vibrations.
Another object of the present invention is to provide an anti-vibration apparatus capable of efficiently suppressing disturbance vibrations even when the center of gravity of an apparatus mounted on an anti-vibration bed shifts.
Still another object of the present invention is to provide an anti-vibration apparatus capable of suppressing the generation of heat from an actuator.
A further object of the present invention is to provide an exposure apparatus capable of efficient vibration control independently of the movement of a stage mounted on a base plate.
A still further object of the present invention is to provide an exposure apparatus capable of efficient vibration control without affecting the environmental temperature.
A still further object of the present invention is to provide an exposure apparatus capable of improving the exposure accuracy.
To attain the above-described objects, the present invention provides an anti-vibration apparatus which has an anti-vibration bed (
6
) held horizontally through at least three pneumatic vibration-isolating pads (
4
A to
4
D); a plurality of actuators (
7
A to
7
D;
32
A to
32
C) that drive the anti-vibration bed vertically at different positions; displacement sensors (
10
A to
10
C) that detect a displacement of the anti-vibration bed; vibration sensors (
5
x
to
5
z
) that detect vibrations of the anti-vibration bed; a first control system (
11
) that controls each of the actuators to suppress the vibrations of the anti-vibration bed on the basis of the outputs of the displacement and vibration sensors; and a second control system (
37
) that controls the flow rate of air supplied to the vibration-isolating pads according to the amount of inclination of the anti-vibration bed.
By virtue of the above arrangement, the flow rate of air is controlled according to the amount of inclination of the anti-vibration bed. Accordingly, the whole or a part of the inclination of the anti-vibration bed can be corrected by the vibration-isolating pads; therefore, it is possible to correspondingly reduce the thrust to be generated from the actuators. Thus, the generation of heat from the actuators is favorably suppressed.
To attain the above-described objects, the present invention also provides an anti-vibration apparatus which has an anti-vibration bed (
6
) held horizontally through at least three pneumatic vibration-isolating pads (
4
A to
4
D); a plurality of actuators (
7
A to
7
D;
32
A to
32
C) that drive the anti-vibration bed vertically at different positions; displacement sensors (
10
A to
10
C) that detect a displacement of the anti-vibration bed; vibration sensors (
5
x
to
5
z
) that detect vibrations of the anti-vibration bed; a first control system (
11
) that controls each of the actuators to suppress the vibrations of the anti-vibration bed on the basis of the outputs of the displacement and vibration sensors; a second control system (
37
) having air controllers (
37
A to
37
C) for controlling the flow rate of air supplied to the vibration-isolating pads, thereby correcting an inclination of the anti-vibration bed; and buffer tanks (
109
A to
109
D) provided between the vibration-isolating pads and the air controllers.
By virtue of the above arrangement, the flow rate of air supplied to the vibration-isolating pads is controlled through the air controllers so that an inclination of the anti-vibration bed is corrected. During this control, air flows into the buffer tanks from the air controllers, and thereafter the air is supplied to the vibration-isolating pads. Therefore, a rapid change of the pressure in the vibration-isolating pads is suppressed by the action of the buffer tanks. Accordingly, it is possible to prevent the occurrence of a hop, or other similar undesired phenomenon, on a stage mounted on the anti-vibration bed, for example.
To attain the above-described objects, the present invention also provides an exposure apparatus which has an anti-vibration bed held horizontally thr
Armstrong, Westerman Hattori, McLeland & Naughton
Miller Rose M.
Nikon Corporation
Williams Hezron
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