Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-06-13
2003-01-07
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S053000, C355S055000, C355S062000, C355S068000, C355S072000, C355S077000, C430S311000, C430S312000, C250S492200, C250S492220, C248S188200, C248S638000
Reexamination Certificate
active
06504599
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a stage apparatus used for, e.g., a fine moving stage for finely aligning a substrate such as a wafer or a master such as a reticle in an exposure apparatus or the like, an exposure apparatus, and a device manufacturing method.
BACKGROUND OF THE INVENTION
Control techniques for industrial and information devices are increasing in precision and speed as such devices become complicated, advanced, and miniaturized. Exposure apparatuses for manufacturing “semiconductor devices” which support various types of such devices are also rapidly increasing in speed and precision, and demands are arising for nm-order alignment precision and the like.
A generally known alignment mechanism for a wafer and reticle in an exposure apparatus is a stage apparatus constituted by a fine moving stage having a microtranslation mechanism and fine rotation mechanism, and a coarse moving stage having a large-stroke moving mechanism in the translational direction.
Such an exposure apparatus finely aligns, controls, and exposes a wafer or reticle on the fine moving stage so as to make it coincide with the image or object plane by the fine moving stage mounted on the coarse moving stage while the coarse moving stage makes large-stroke movement.
In general, both the coarse and fine moving stages often use linear motors, which utilize a Lorentz force, as the actuator of the alignment mechanism.
However, the fine moving stage of the exposure apparatus has recently been found to suffer from the following problems.
(1) As chips, wafers, and reticles increase in size, the fine moving stage also increases in size. Pushing up the fine moving stage by a linear motor using a Lorentz force consumes a large amount power.
Especially the actuator of the fine moving stage is often attached near a wafer or reticle. Compared to the coarse moving stage, the fine moving stage greatly influences the wafer or reticle to thermally deform it, resulting in very low final exposure precision.
(2) Demands are arising for a high-speed exposure apparatus, and the acceleration of the coarse moving stage is being increased. This means that the acceleration applied from the coarse moving stage to the fine moving stage also increases. When the coarse moving stage accelerates the fine moving stage, a moment force proportional to the acceleration of the coarse moving stage acts on the fine moving stage due to the difference between the barycenter of the fine moving stage and a “point of application” where the actuator of the coarse moving stage pushes the fine moving stage.
Hence, as the speed increases, the actuator of the fine moving stage becomes bulky in order to withstand the moment force, and the amount of heat generated by the actuator increases to adversely influence the exposure precision. In other words, a bulky actuator increases heat, which is a vicious cycle.
As a means for solving these problems, there is provided a method of compensating for the weight of the fine moving stage by using the repulsion and attraction forces of a magnet or electromagnet. In this case, it is difficult to hold the posture of the fine moving stage by compensation with only the magnet, so a spring is also used to hold the posture.
FIGS. 5A and 5B
schematically show a conventional wafer stage for compensating for the weight by magnetic repulsion. This wafer stage comprises a fine moving stage
101
having a support surface
101
a
for supporting a wafer WO, a coarse moving stage
102
having a large-stroke moving mechanism (not shown), first to third spring members
103
a
to
103
c
for holding the posture of the fine moving stage
101
on the coarse moving stage
102
, and first to third magnetic units
104
a
to
104
c
for compensating for the weight by a so-called magnetic repulsion force for supporting the weight of the fine moving stage
101
. The magnetic units
104
a
to
104
c
are respectively made up of magnets
141
a
to
141
c
fixed to the upper surface of the coarse moving stage
102
and magnets
142
a
to
142
c
fixed to the lower surface of the fine moving stage
101
so as to face the corresponding magnets
141
a
to
141
c.
The weight of the fine moving stage
101
is compensated for by the magnetic repulsion forces of the magnets
141
a
to
141
c
and
142
a
to
142
c
of the magnetic units
104
a
to
104
c
. When the wafer W
0
is aligned near the image plane of a projection optical system (not shown), the weight of the fine moving stage
101
is canceled by the magnetic repulsion force.
The three spring members
103
a
to
103
c
for compensating for the posture of the fine moving stage
101
have the same spring constant, which is set to minimize the restoring forces of the springs while the wafer W
0
is near the image plane.
The fine moving stage
101
has a pair of bar mirrors
110
for detecting the position of the fine moving stage
101
by a laser interferometer or the like. This wafer stage is equipped with a control system for feeding back the detected position information of the fine moving stage
101
to the actuator of the coarse moving stage
102
.
The three posture compensation spring members
103
a
to
103
c
are generally arranged at positions Z
1
to Z
3
at equal intervals of 120° on a circle of a radius r having a geometrical center O of the fine moving stage
101
as its center.
In this prior art, however, the barycenter of a structure formed from the members and fine moving stage is at a position different from the geometrical center of the fine moving stage, i.e., the geometrical centroid of a triangle formed by the support points Z
1
to Z
3
of the spring members
103
a
to
103
c
under the influence of the members such as the bar mirrors fixed to the fine moving stage for holding a wafer. The restoring forces of the three spring members necessary for pushing up the fine moving stage only in the +Z direction without rotating it and for keeping it at a predetermined pushed-up position and posture are different.
Accordingly, holding the posture by the three springs having the same spring constant causes the following problems even if the magnets compensate for the weight of the fine moving stage. Assume that the fine moving stage is vertically displaced in the −Z direction without rotating it, and the springs uniformly deflect. In this case, the sum of the restoring forces of the three springs not only translates the fine moving stage in the +Z direction but also rotates it.
More specifically, if an external force acts on the fine moving stage owing to some factor while position control by the actuator of the fine moving stage stops, or if position control stops due to an emergency stop caused by an accident while the fine moving stage is displaced in the −Z direction by the actuator, restoring motion of the fine moving stage in the +Z direction and tilt motion exceeding a moving stroke in the rotational direction occur, scoring or damaging the stage.
There is proposed a method of compensating for the weight of the fine moving stage by magnets, compensating for the posture by springs, and generating a uniform weight compensation force by the magnets in almost the entire range of the Z-direction stroke on the fine moving stage. Even this method requires a posture holding means using coil springs or leaf springs because compensation by only magnets is unstable. This method cannot solve the static unbalance.
There is also proposed a method of directly compensating for the weight of the fine moving stage by springs. Even this method cannot solve the above problems.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a stage apparatus which uses at least three spring members in order to compensate for the weight of a stage for setting a wafer or reticle, can improve the stability of a compensation function by the spring members, and can effectively avoid scoring of or damage to the stage, to provide an exposure apparatus including the stage
Adams Russell
Brown Khaled
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