Measuring and testing – Vibration – Vibrator
Reexamination Certificate
2003-02-19
2004-06-01
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Vibrator
C188S378000, C267S136000, C248S550000
Reexamination Certificate
active
06742393
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vibration control apparatus and method used when the vibration of a movable element influences the control accuracy in a field where high-speed, high-accuracy position/speed control is required for a semiconductor exposure apparatus, machine tool, OA device, and the like.
BACKGROUND OF THE INVENTION
A prior art will be described by exemplifying stage control of a semiconductor exposure apparatus.
As the exposure line width has decreased in a semiconductor exposure apparatus, the position control accuracy required for the wafer stage of the exposure apparatus has reached several nm order. For higher productivity, the stage moving acceleration and speed are increasing year by year. To realize high-speed, high-accuracy position control, the wafer stage position control system must have a high servo band. A high servo band exhibits a high response characteristic to a target value, realizing a system resistant to the influence of disturbance or the like. In manufacturing an apparatus, the wafer stage and main body structure are so designed as to realize a servo band as high as possible.
FIG. 10
is a view showing the schematic arrangement of the wafer stage of a conventional semiconductor exposure apparatus. In the following description, three translation axes (X, Y, and Z) of standard coordinates and three rotation axes (&thgr;x, &thgr;y, and &thgr;z) around the three translation axes will be called a position with six degrees of freedom. The arrangement and operation of a high-speed, high-accuracy position control system will be explained using this example.
Reference numeral
41
denotes a surface plate which is supported via a damper from a floor F; and
43
, a Y stage which can be moved in the Y direction on the reference plane of the surface plate
41
by Y linear motors
46
for generating a thrust in the Y direction along a guide
42
fixed to the surface plate
41
. The surface plate
41
, fixed guide
42
, and Y stage
43
are coupled in a noncontact manner by air via air pads
44
a
and
44
b
serving as hydrostatic bearings. The Y stage
43
has an X guide, which guides an X stage
45
mounted on the Y stage in the X direction. The Y stage
43
has an X linear motor stator which generates a force in the X direction. The X linear motor stator drives the X stage
45
in the X direction together with an X linear motor movable element mounted on the X stage. The surface plate
41
, X guide, and X stage
45
are coupled in a noncontact manner by air via an air pad
44
c
serving as a hydrostatic bearing.
The X stage
45
supports a tilt stage
48
. The tilt stage
48
moves in the Z direction and rotates along the three axes (&thgr;x, &thgr;y, and &thgr;z) by a thrust from a linear motor (not shown). The tilt stage
48
supports a stage plate
51
having a wafer chuck, which holds a wafer
53
to be exposed. Measurement mirrors
49
a
and
49
b
used to measure X and Y positions are arranged on the stage plate
51
.
The stage device of the semiconductor exposure apparatus is aligned with six degrees of freedom in in-plane directions (X, Y, and &thgr;z) and vertical directions (Z, &thgr;x, and &thgr;y) with respect to the reference plane of the surface plate, and performs exposure of one chip. Positions in the in-plane directions (X, Y, and &thgr;z) are measured using a laser interferometer
50
integrated with a lens barrel (not shown). As for measurement in the tilt directions (Z, &thgr;x, and &thgr;y), a Z position and the angle of a rotational component are measured by an alignment measurement system (not shown) integrated with the lens barrel.
In
FIG. 10
, the lens barrel is assumed to be integrated with the surface plate, and the laser interferometer
50
is connected to the surface plate. Although no Z measurement device is illustrated, the tilt directions (Z, &thgr;x, and &thgr;y) can be measured by measuring three points on the stage plate or wafer from the lens barrel.
Alignment along the six axes is achieved by arranging a servo system for each axis. A compensation device calculates driving command values to the X and Y linear motors serving as X and Y stage actuators on the basis of position information of the laser interferometer, driving the X and Y stages. The compensation device calculates a driving command value to the tilt stage in accordance with the Z position, the angles in the rotational directions (&thgr;x and &thgr;y), and the &thgr;z measurement value, driving the tilt stage.
The position control system having this arrangement can move the wafer stage to a target position at a high speed and high accuracy.
The resolution of the exposure line width is high in the stage device of the semiconductor exposure apparatus, and the position control accuracy must be high. Also, the semiconductor exposure apparatus, which is a production equipment, must have high throughput in terms of productivity. To meet these demands, the stage servo system must have a high response characteristic and move at a high speed. To increase the stage position control accuracy, the designer realizes a high servo band by setting the gain of the position control system as high as possible. However, if the designer tries to set the gain higher, its upper limit is restricted by the oscillation of the servo system. The servo band is restricted by various factors, one of which is the elastic vibration of a mechanical system in the control loop.
FIG. 8
shows the analysis result of the elastic vibration mode of the wafer stage plate
51
. The primary to quaternary elastic vibration modes are illustrated. Such a thin plate is low in Z rigidity and vibrates by elastic deformation such as bending or twist. The transfer characteristic from the Z actuator to a measurement point at this time is shown in
FIG. 9
, and the resonance point of elastic vibration has a high peak. If, for example, the loop gain of the Z position control system is increased in this system, the resonance point of elastic vibration is excited, decreasing the stage control accuracy. With a loop gain low to a given degree, merely a large vibration appears. With a higher gain, the servo system becomes unstable and oscillates.
In this fashion, the stage plate (top plate) and the like generate elastic vibrations, and the servo system becomes unstable. Even if the servo system does not become unstable, the control error increases, failing to satisfy control specifications. In general, the servo band is restricted to about ⅓ to ¼ the lowest resonance frequency of the elastic vibration.
In the conventional position control system, the servo band of the position control system is restricted by the resonance frequency of the elastic vibration of an object to be controlled. To realize a higher servo band, the resonance frequency of the elastic vibration must be increased, or the damping characteristic must be enhanced. For this purpose, the rigidity of an object to be controlled is increased, its mass is decreased, or the damping characteristic of the elastic vibration is enhanced. However, mechanical measures such as a decrease in stage mass, an increase in rigidity, and enhancement of the damping characteristic are limited, and it is difficult to increase the servo band.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the conventional drawbacks, and has as its object to constitute a high-accuracy position control system even for a low-rigidity object to be controlled.
To solve the above-described problem and achieve the above object, according to the first aspect of the present invention, a vibration control apparatus is characterized by comprising a measurement device which measures an elastic vibration of an object to be controlled, a driving device which applies a force to the object, and a compensation device which determines a force to be generated by the driving device, wherein the measurement device measures at least a position component out of the position component, a speed component, and an acceleration component of the el
Canon Kabushiki Kaisha
Saint-Surin Jacques
Williams Hezron
LandOfFree
Vibration control apparatus, vibration control method,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vibration control apparatus, vibration control method,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vibration control apparatus, vibration control method,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3359964