Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-12-29
2003-11-25
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C318S623000, C318S625000
Reexamination Certificate
active
06654098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stage apparatus used in a semiconductor exposure apparatus or a testing apparatus, for positioning an object to be exposed, a mask having an original pattern to be transferred, or an object to be tested, to a desired position. The present invention also relates to an exposure apparatus using such a stage apparatus and to a method of producing a device using such an exposure apparatus.
2. Description of the Related Art
Steppers and scanners are widely used as exposure apparatuses in the production of semiconductor devices. A stepper is an apparatus for projecting an image of a pattern formed on a reticle onto a wafer via a projection lens so as to form an image of the pattern with a reduced size on the wafer while moving, in a step-by-step fashion, the semiconductor wafer placed on a stage apparatus and below the projection lens, thereby exposing the wafer shot by shot. In a scanner, on the other hand, a semiconductor wafer placed on a wafer stage and a reticle placed on a reticle stage are moved relative to a projection lens, and exposure light in the form of a slit is emitted when the wafer and the reticle are being moved and scanned so as to project a reticle pattern onto the wafer. The steppers and scanners are widely used as exposure apparatuses because of their high performance in terms of the resolution and registration accuracy.
FIG. 5
illustrates an example of a conventional exposure apparatus. As shown in
FIG. 5
, the exposure apparatus is constructed on a base frame
1
installed on a floor of a factory. A lens barrel base
2
is supported on the base frame
1
. A reduction optical system
3
, a reticle stage
4
on which a reticle including an original pattern to be transferred is placed, and an alignment optical system (not shown) are disposed on the lens barrel base
2
. In order to avoid the influence of vibrations of the floor on which the apparatus is installed, the lens barrel base
2
is placed on a vibration isolating mechanism
5
using an air spring or the like. In the case of an exposure apparatus of the stepper type, the reticle stage
4
is driven within a small range. In contrast, in the case of an exposure apparatus of the scanner type, the reticle stage
4
is scanned in synchronization with the scanning of a wafer stage
6
which will be described later.
A wafer stage base
7
serving as a guide for horizontally guiding the wafer stage
6
is disposed on the base frame
1
. The wafer stage
6
is made up of two stages which can be moved in two directions (X and Y directions) perpendicular to each other so as to carry a wafer in a horizontal plane. More specifically, the wafer stage
6
is made up of a Y stage movable in the Y direction and an X stage which is disposed on the Y stage and which is movable in the X direction. Hydrostatic bearings are disposed between the wafer stage base
7
and the X and Y stages and between the X stage and the Y stage such that the X and Y stages can move with very low friction in the intended moving directions but such that they are supported very rigidly in the direction perpendicular to the moving plane. Therefore, when the Y stage is driven, the X stage moves together with the Y stage. A magnet serving as a mover of a linear motor is disposed on the Y stage, and a stator (in the form of a coil) of the linear motor is disposed on the stage base
7
so that the Y stage is driven by a force generated between the mover and the stator of the linear motor. Similarly, a mover of a linear motor is disposed on the X stage, and a stator of the linear motor is disposed on the Y stage such that a driving force is generated between the mover and the stator. The reaction force of the driving force applied to the X stage acts upon the Y stage and is received by the guide formed on the stage base
7
, and thus the X stage is driven in the X direction with respect to the stage base
7
.
A fine adjustment stage
8
, capable of finely adjusting the position in a rotational direction in the XY plane, in a direction normal to the XY plane, in a rotational direction about the X axis, and in a rotational direction about the Y axis, is disposed on the X stage (the fine adjustment stage
8
will not be described in further detail herein). A wafer to be exposed is placed on a wafer chuck (not shown) on the fine adjustment stage
8
. The position of the wafer stage
6
is measured using a high-resolution laser interferometer. In order to achieve high precision positioning of the wafer stage
6
, a stage control system is used although it is not shown in FIG.
5
. On the basis of the target value of the wafer stage position generated by a main controller (not shown) and the wafer stage position measured by the laser interferometer, the stage control system sends a drive command signal to an actuator of the wafer stage
6
. In accordance with the drive command signal, the respective linear motors of the wafer stage
6
are driven by linear motor driving amplifiers (not shown) and generate driving forces in particular directions.
One measure of the performance of the exposure apparatus is the number of wafers which can be handled per unit time (throughput). The wafer stage
6
is moved when a wafer is exchanged, alignment (positioning of the wafer with respect to the exposure optical system) is performed, and the wafer is moved such that each shot area (area to be exposed) of the wafer comes to an exposure position. The moving time of the wafer stage
6
has a large ratio to the total time required to process one wafer. Therefore, to increase the throughput, it is necessary to reduce the time required to move the wafer stage
6
in the X and Y directions. In order to quickly move the wafer stage, it is necessary not only to increase the moving speed but also to quickly perform the acceleration and deceleration. The driving force of the wafer stage
6
is given by the product of the mass of the wafer stage
6
and the acceleration exerted thereon. The reaction force of the driving force applied to the Y stage is transmitted to the base frame
1
via the stage base
7
and further to the floor. The reaction force of the driving force applied to the X stage is transmitted to the base frame
1
via the stage base
7
and further to the floor. If the reaction forces of the driving forces applied to the X and Y stages are great, the base frame
1
and the floor are vibrated. The vibration of the base frame
1
or the floor causes degradation in the positioning accuracy of the wafer stage
6
. Besides, because the performance of the vibration isolating mechanism is limited, the vibration is also transmitted to the lens barrel base
2
, and the exposure accuracy is degraded. Furthermore, the vibration of the floor exerts an influence upon other apparatus installed at nearby locations.
One known technique to avoid the transmission of the reaction force of the stage driving force to the base frame
1
and the floor is shown in FIG.
6
. In this technique, a base
9
is disposed upon a floor such that the base
9
is allowed to freely move in a horizontal direction, and a stage
10
is supported on the base
9
such that the stage
10
is allowed to freely move in the horizontal direction. If a driving force f is applied between the base
9
and the stage
10
, an acceleration of &agr;=f/m is exerted upon the stage
10
, and an acceleration of &bgr;=f/M is exerted upon the base
9
in a direction opposite to the direction in which the stage
10
is accelerated, where m is the mass of the stage
10
and M is the mass of the base
9
. That is, in response to accelerations inversely proportional to the masses applied to the stage
10
and the base
9
, the stage
10
and the base
9
are moved. However, the reaction forces of the driving force result in the accelerations, and they are cancelled and are not transmitted to the floor.
In the system shown in
FIG. 6
, because the motion of the stage
10
always occurs with respect to the base
9
, the posi
Asano Toshiya
Ukaji Takao
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