Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1997-07-28
2001-01-23
Moses, Richard (Department: 2852)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C355S072000, C355S075000
Reexamination Certificate
active
06177978
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to an exposure apparatus such as a semiconductor exposure apparatus and, more particularly, to a scanning stage device suitably usable in a scanning type exposure apparatus wherein an arcuate or rectangular slit-like region of a pattern of a reticle is imaged on a substrate such as a wafer and wherein both the reticle and the substrate are scanningly moved so that the reticle pattern as a whole is exposed and transferred to the substrate.
In a scanning type exposure apparatus wherein both a reticle (original) and a substrate are scanningly moved so that a reticle pattern as a whole is transferred onto the substrate, it is necessary to control the scanning speed of the reticle or the substrate very precisely and stably. Generally, for this purpose, a scanning exposure apparatus is provided with linear motor means which is, as shown in
FIG. 14
, incorporated into driving means of a scanning stage device for holding and scanningly moving a reticle or a substrate. The illustrated device comprises a base
101
, a guide
102
fixed to the base
101
and having a U-shaped sectional shape, and a wafer stage
103
movable reciprocally in a predetermined direction (scan direction) along the guide
102
. The device further comprises a pair of linear motor stators
104
and
105
disposed at opposite sides of the movement path of the wafer stage
103
, which is movable along the guide
102
, and being provided integrally with the base
101
. The device further comprises a pair of linear motor movable elements
106
and
107
which are provided integrally with the sides
103
a
and
103
b
of the wafer stage
103
, respectively. The linear motor stators
104
and
105
and the linear motor movable elements
106
and
107
constitute a pair of linear motors E
1
and E
2
for providing acceleration and deceleration of the wafer stage
103
in the scan direction. The wafer stage
103
is guided by the guide
102
without contact thereto, through association of static pressure bearing means (not shown), for example.
The linear motor stators
104
and
105
have elongated loop-like yokes
104
a
and
105
a
, extending along and substantially throughout the length of the guide
102
, and elongated magnets
104
b
and
105
b
fixed to the insides of the yokes
104
a
and
105
a
, respectively. The magnets
104
b
and
105
b
extend through coil openings
106
a
and
107
a
, respectively, of the linear motor movable elements
106
and
107
, respectively. When the linear motor movable elements
106
and
107
are energized in response to supply of drive currents from a voltage source (not shown), thrust forces are produced along the magnets
104
b
and
105
b
by which the wafer stage
103
is accelerated or decelerated.
Wafer W
0
is attracted to the wafer stage
103
and, above the wafer, a reticle is held by a reticle stage
203
(see FIG.
17
). By means of slit-like exposure light L
0
(its section being depicted by a broken line) impinging on a portion of the reticle, a slit-like region of the wafer W
0
is exposed such that a portion of the reticle pattern is transferred to that region. Each exposure cycle of the scanning type exposure apparatus comprises moving both the wafer stage
103
and the reticle stage
203
so that the reticle pattern as a whole is transferred to the wafer W
0
. During movement of the wafer stage
103
which holds the wafer W
0
, the position thereof is detected by means of a laser interferometer
108
(FIG.
17
). The reticle stage
203
has similar driving means such as described above, and it is controlled in a similar way. Speed control during acceleration and deceleration of the wafer stage
103
through the linear motors E
1
and E
2
, is performed in the following manner.
FIG. 15
is a top plan view of the scanning stage device of FIG.
14
. When, for example, the wafer stage
103
is at the leftward end position in the scan direction as viewed in the drawing and the center O
0
of the width of the wafer W
0
in the scan direction is at the acceleration start position P
1
, acceleration by rightward thrust of the linear motors E
1
and E
2
as viewed in the drawing starts. Acceleration stops when the center O
0
of the wafer W
0
comes to the acceleration end position P
2
. After this, the liner motors E
1
and E
2
serve only to control and maintain a constant scanning speed of the wafer stage
103
. When the center O
0
of the wafer W
0
comes to the deceleration start position P
3
, deceleration by leftward thrust of the linear motors E
1
and E
2
as viewed in the drawing starts. When the center O
0
of the wafer W
0
comes to the deceleration end position P
4
, running of the wafer stage
103
stops. Simultaneously therewith, leftward acceleration as viewed in the drawing starts. Moving the wafer stage
103
leftwardly, as viewed in the drawing, is performed by controlling the linear motors E
1
and E
2
in a similar way but in the opposite direction.
In such an acceleration and deceleration cycle, if for example the wafer stage
103
runs rightwardly as viewed in the drawing, the exposure process starts just when the center O
0
of the wafer W
0
comes to the acceleration end position P
2
, such that the exposure light L
0
impinges on a rightward end slit-like region of the wafer W
0
as viewed in the drawing. When the center O
0
of the wafer W
0
comes to the deceleration start position P
3
, the exposure of the whole surface of the wafer W
0
is completed. Thus, during exposure of the wafer W
0
, the wafer stage
103
moves at a constant scanning speed, and the reticle (not shown) moves similarly. The relative position of the wafer W
0
and the reticle at the time of starting of the exposure process is controlled precisely, and the speed ratio of the wafer W
0
and the reticle is controlled so that it exactly corresponds to the reduction magnification of a projection optical system disposed between the wafer and the reticle. After completion of the exposure process, both the wafer and the reticle are decelerated appropriately.
For a higher productivity of a scanning type exposure apparatus, it is desirable to reduce, as much as possible, the time to be consumed by the acceleration and deceleration of the linear motors E
1
and E
2
. Also, from the viewpoint of saving space, the moving distance of the wafer stage
103
during acceleration and deceleration of the linear motors E
1
and E
2
should desirably be short. This requires that the linear motors E
1
and E
2
provide a large thrust and also that the strength of the magnetic field of the linear motor stators
104
and
105
is very large, such as about 5,000 G., for example. In order to meet this requirement, the yokes
104
a
and
105
a
may be made of a material such as iron, for example, having a high saturation magnetic flux density, but even on such an occasion it is still necessary that the opposite end portions
104
c
and
105
c
(
FIG. 16
) of the yokes
104
a
and
105
a
, where the magnetic flux of the magnetic field is strong such as discussed above is concentrated, have a very large sectional area so as not saturate the concentrated magnetic flux.
In the arrangement described above, the opposite end portions of the yokes of the linear motor stators should have a very large sectional area so as to avoid saturation of the magnetic flux. Additionally, the central portion of the yoke (where acceleration or deceleration of a wafer stage, for example, is not necessary) has the same sectional size of the end portion thereof. As a result, the yoke as a whole has a very large weight. Thus, the device as a whole is very large and very heavy. Also, for producing a large magnetic field as described above, the magnet of the linear motor stator should have a large thickness, and it should be made of a rare earth magnet which is very expensive. If a thick and expensive magnet is provided along the entire running path of the scanning stage, the cost of the linear motor becomes very high.
Further, as shown in
FIG. 17
, as r
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Moses Richard
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