Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
2002-03-22
2004-11-30
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C318S489000, C248S638000
Reexamination Certificate
active
06825635
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a vibration isolator used in a semiconductor manufacturing apparatus and/or an electron microscope, etc. More particularly, the invention relates to a vibration isolator, referred to as an active vibration isolator, for driving an actuator in accordance with a detection signal from a vibration sensor. The invention further relates to a device manufacturing apparatus such as an exposure apparatus having the above-mentioned vibration isolator, a device manufacturing method, a semiconductor manufacturing plant and a method of maintaining the device manufacturing apparatus.
BACKGROUND OF THE INVENTION
In precision instruments such as electron microscopes and semiconductor device manufacturing apparatus, the transfer of vibration from the external environment to the apparatus proper must be minimized.
It is essential, therefore, that the precision equipment be mounted on a precision vibration isolator. In particular, since an XY stage for exposure in an exposure apparatus moves continuously and at high speed, it is required that the vibration isolator achieve, in good balance, a vibration isolating capability with regard to external vibration and a vibration damping capability with regard to internal vibration produced by operation of the mounted equipment itself.
An active-type vibration isolator has been put into practical use in recent years to meet these requirements. Such a vibration isolator makes it possible to control vibration effectively by driving an actuator in accordance with a detection signal from a vibration sensor. The active vibration isolator makes it possible to achieve balanced vibration isolating and vibration damping capabilities. This is difficult to realize with a passive vibration isolator that relies solely upon a support mechanism having spring and damper characteristics.
A typical embodiment of a vibration isolator seen in the prior art is disclosed in the specification of Japanese Patent Application Laid-Open No. 10-156144, entitled “Vibration Isolator”. In accordance with this disclosure, acceleration sensors are adopted as vibration sensors for sensing the vibration of a vibration isolation platform, and air springs are adopted as actuators for driving the vibration isolation platform. The acceleration sensors are arranged with their axes of detection pointing in the horizontal and vertical directions and detect acceleration of the vibration isolation platform in the horizontal and vertical directions.
The air springs, which support the vibration isolation platform in such a manner that their thrust producing axes agree with the horizontal and vertical directions, apply horizontal and vertical thrust to the vibration isolation platform. Vibration of the vibration isolation platform is suppressed in excellent fashion by applying so-called vibration feedback in accordance with which the air springs drive the vibration isolation platform along the horizontal and vertical directions in accordance with compensation values obtained by applying appropriate compensation to the detection signals from the acceleration sensors.
In a precision vibration isolator of this kind, it is common knowledge to use servo-type acceleration sensors, which exhibit excellent resolution with respect to minute vibration, for the purpose of sensing vibration of the vibration isolation platform. The principle of acceleration detection by a servo-type acceleration sensor will be described with reference FIG.
6
A.
FIG. 6A
illustrates an arrangement where a servo-type acceleration sensor is disposed in the horizontal direction. A case is fixed to a mounting surface and a pendulum is suspended from the case. Acceleration produced at the mounting surface is equal to an inertial force that acts upon the pendulum. In this servo-type acceleration sensor, a servo mechanism is provided in such a manner that the displacement of the pendulum is maintained at zero. The velocity of the mounting surface is sensed using a servo electromagnetic force.
The servo-type acceleration sensor also senses inclination of the mounting surface using the earth's gravitational force, as shown in FIG.
6
B. Thus, while the servo-type acceleration sensor is advantageous in that it can sense even DC components of acceleration, it is disadvantageous in terms of controlling vibration precisely.
More specifically, in a case where the servo-type acceleration sensor is disposed on a horizontal plane in order to sense acceleration in the horizontal direction and the horizontal direction is the direction of interest, a problem which arises is that inclination of the mounting surface, which is regarded as another component, also is sensed. The fact that another component is included in the detection signal is equivalent to application of measurement noise to the vibration-control feedback loop. This is a factor that impedes an improvement in the performance of the vibration isolator. If horizontal vibration feedback in the horizontal direction is applied in an active vibration isolator, vibration feedback cannot be applied properly because the detection signal includes another component that represents inclination. As a consequence, the vibration isolation platform is caused to vibrate instead of having its vibration suppressed.
A servo-type velocity sensor of the kind disclosed in the specification of Japanese Utility Model Publication No. 6-28698 (entitled “Servo-type Vibration Receiver”) also has been put into practical use in recent years. Since velocity is obtained by an integration of acceleration, a velocity sensor is advantageous in that it has a low-frequency sensitivity that is higher than that of an acceleration sensor. Velocity sensors are utilized in architectural structures and in the measurement of ground vibration where observation of low-frequency components is important.
However, the principle of velocity detection by a servo-type velocity sensor is similar to the principle of acceleration detection by a servo-type acceleration sensor that uses a pendulum of the kind shown in
FIGS. 6A and 6B
. When velocity in the horizontal direction is sensed by a servo-type vibration sensor, the aforementioned problem still arises, namely, the fact that other components ascribable to inclination also are sensed.
Exactly the same problem arises also when a servo-type acceleration sensor or servo-type velocity sensor is disposed in the vertical direction. The sensor will sense not only vertical translational vibration but also inclination of the sensor mounting surface with respect to the vertical axis. As a consequence, when vibration feedback in the vertical direction is applied in an active-type vibration isolator, vibration feedback cannot be applied properly because the sensor signal includes inclination-related components. As a consequence, the vibration isolation platform is caused to vibrate instead of having its isolation suppressed.
In other words, because a sensor-type vibration isolator whose use in a precision vibration isolator is common knowledge is influenced by inclination of the vibration isolation platform, the performance of the vibration isolator is degraded when vibration feedback is applied.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a vibration isolator for sensing vibration only in a horizontal translational direction or vertical translational direction without being affected by inclination of a vibration isolation platform, thereby making it possible to control vibration in an ideal fashion, as well as a device manufacturing apparatus and method, a semiconductor manufacturing plant and a method of maintaining the device manufacturing apparatus that employ the vibration isolator.
According to the present invention, the foregoing object is attained by providing a vibration isolator comprising: a vibration isolation platform, a vibration sensor installed on the vibration isolation platform, and an angle sensor for sensing an inclination angle of the vibration isolation platform, wherein a detect
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ro Bentsu
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