Photocopying – Projection printing and copying cameras – Detailed holder for original
Reexamination Certificate
1999-07-26
2003-05-27
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for original
C355S053000, C355S072000, C355S077000, C399S078000, C250S492200, C250S492220
Reexamination Certificate
active
06570645
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to a stage system in which high precision positioning performance is required. The invention relates also to an exposure apparatus having such stage system for carrying a reticle or a wafer thereon for exposure of the same, and to a device manufacturing method using such exposure apparatus. In another aspect, the invention relates to a stage driving method effective to perform high precision positioning.
FIGS. 15A and 15B
are schematic views of an example of known type stage system. A guide
802
is fixed to a base (not shown), and a stage
801
for carrying a workpiece
800
thereon is supported by the guide
802
slidably along one axial direction relative to it. There are linear motor moving elements
804
fixed at the opposite sides of the stage
801
. Each moving element
804
faces to a linear motor stator
805
without contact thereto. The linear motor stators
805
are fixed to the base, not shown. Each linear motor moving element
804
comprises upper and lower integral structures of four-pole magnets
804
a
and yokes
804
b
for circulation of magnetic fluxes of the magnets. Each linear motor stator
805
comprises a plurality of coils
805
a
(six in this example) disposed in an array and being fixed together by a stator frame
805
b.
The linear motor
803
described above is an extended type of ordinary brushless DC motor, wherein the driving coil and the direction of electric current thereto are changed in accordance with the relative positional relationship between the magnet
804
a
and the coil
805
a
, whereby a desired force is produced in a desired direction.
In the structure described above, first, while the stage
801
is held stationary, an electric current is applied to predetermined linear motor coils in a predetermined direction and for a predetermined time period in accordance with the position of the stage
801
or of the magnets
804
a
, to produce acceleration of the stage
801
. When a desired speed is reached, acceleration is finished and, while constant speed control is kept, a predetermined operation such as exposure or inspection, for example, is performed. After the constant speed period, an electric current is applied to predetermined linear motor coils in a predetermined direction and for a predetermined time period, to cause deceleration of the stage and to stop the stage motion.
The position of the stage is measured by using high precision position sensor means (not shown) such as a laser interferometer, for example, and an electric current is applied to linear motor coils separately from acceleration or deceleration, so as to avoid an error with respect to a target position. Thus, even during acceleration period, deceleration period and constant speed period, high precision position control is performed.
FIG. 16
is a schematic view of another example of known type stage system. This stage system is similar to one disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 183192/1995. A guide
909
is mounted on a base
903
, and a stage
907
is supported slidably relative to the guide
909
. The base
903
is provided with an actuator unit
901
which serves to perform the positioning through expansion and contraction of its rod
905
. Disposed between an end of the rod
905
and the stage
907
are a voice coil motor
906
and a clutch
904
. The motor
906
comprises a coil-and-magnet structure (not shown), and a Lorentz force is produced in response to application of electric current to the coil, whereby a driving force is produced between the rod
905
and the stage
907
.
In the structure described above, for driving the stage, first the clutch
904
is engaged through mechanical contact so that the rod
905
and the stage are held in connection. The driving force of the actuator unit
901
is thus transmitted to the stage, whereby rough motion of the stage is produced. The clutch
904
is disengaged after the stage rough motion, and the stage
907
is driven thereafter relative to the rod
905
with the driving force of the voice coil motor
906
, to accomplish the positioning of the stage
907
.
Since there is clutch
904
in parallel to voice coil motor
906
, it does not need operation of the motor
906
for long-stroke stage driving with the actuator unit
901
. Heat generation of the motor
906
is thus reduced.
When a stage is moved by using a linear motor only as in the first example described above, high precision positioning control is accomplished constantly. However, there is large heat generation in stage acceleration and deceleration. Also, the heat source is close to the workpiece. Further, since in a multi-phase linear motor such as described above the electric current is applied while changing the coils, it is difficult to cool the linear motor stator as a whole. For these reasons, some components adjacent to the workpiece may be deformed by thermal expansion or the measurement reference may be deformed by thermal expansion. Also, the air density along the light path of the laser interferometer may be disturbed. They may cause degradation of workpiece positioning precision. Additionally, thrust ripple to be produced when coils are changed may interfere precise positioning of the stage.
In a case of stage system wherein a voice coil motor and a clutch are provided in parallel between an actuator unit and a stage, as in the second example described above, since the clutch is held in engagement during the stage motion through the actuator unit, the voice coil motor is inoperative. In the rough motion period of the actuator unit, therefore, deviations to the stage target position may be accumulated, which means prolongation of positioning time required for the voice coil motor. Further, since the clutch is based on mechanical contact such as friction, there is a limit to stage precise positioning.
If the voice coil motor is operated while disengaging the clutch, in actuation of the actuator unit, the voice coil motor has to produce a large thrust force which causes large heat generation and lowered stage positioning precision.
Additionally, if the driving stroke of the voice coil motor is short, the stator of the motor must be positioned very precisely with respect to the moving element provided on the stage. In that case, the positioning of the rod by the actuator unit has to be performed vary precisely. However, the rod positioning control through the actuator unit is based on the current position of the stage as measured by the laser interferometer, it is very difficult to accomplish high precision positioning for the rod.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high precision and high speed stage system by which at least one of the problems described above can be solved.
In accordance with an aspect of the present invention, there is provided a stage system, comprising: a stage being movable in a predetermined direction; a first unit for applying a force to the stage in the predetermined direction; moving means for moving one of the first unit and a structure including the first unit; first measuring means for measuring at least one of the position and movement amount of the stage; and second measuring means for measuring at least one of the position and movement amount of one of the first unit and the structure; wherein the stage is controlled on the basis of a measured value of said first measuring means, and wherein said moving means is controlled on the basis of a measured value of said second measuring means.
In preferred forms of this aspect of the present invention, the first unit may be controlled on the basis of a measured value of said first measuring means. The first unit may be controlled on the basis of information related to a target position of the stage. The first unit may include a linear motor. The first unit may have a function applying a force to a gravity center of the stage. The moving means may be controlled on the basis of information related to a target position of the
Ebinuma Ryuichi
Korenaga Nobushige
Adams Russell
Brown Khaled
LandOfFree
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