Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-11-30
2001-07-10
Rutledge, D. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S077000
Reexamination Certificate
active
06259511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus used in a photolithography process in the manufacture of, e.g., a semiconductor element, a liquid crystal display element, a thin-film magnetic head, or the like and, more particularly, to a scanning type exposure apparatus for transferring a pattern on a mask (or a reticle) onto a substrate by synchronously moving the mask and the substrate.
2. Related Background Art
In the photolithography process in the manufacture of semiconductor elements, a projection exposure apparatus for transferring a pattern formed on a mask or reticle (to be generally referred to as a “reticle” hereinafter) onto a substrate (wafer) coated with a photosensitive material (photoresist) via a projection optical system, in particular, a step-and-repeat type reduction production exposure apparatus (stepper), is popularly used. Recently, in association with an increase in size and a decrease in line width of semiconductor elements, it has been required to widen the image field of the projection optical system and to improve the resolution of the projection optical system. However, it is very difficult in terms of design and manufacture to realize both the high resolution and the wide field of the projection optical system. Thus, as disclosed in, e.g., U.S. Pat. Nos. 4,747,678, 4,924,257, 5,194,893, and 5,281,996, a scanning type exposure apparatus, which illuminates only a partial area having a predetermined shape (e.g., a rectangular shape, arcuate shape, hexagonal shape, rhombic shape, or the like) on a reticle with light, and exposes a pattern on the reticle onto a wafer by synchronously moving the reticle and wafer along a direction perpendicular to the optical axis of the -projection optical system, is receiving a lot of attention. In the scanning type exposure apparatus, even when the image field of the projection optical system is small, a large-area pattern image can be exposed onto the wafer, and the resolution of the projection optical system can be relatively easily improved.
FIG. 5A
illustrates a conventional scanning type projection exposure apparatus. Referring to
FIG. 5A
, exposure light EL emerging from an illumination system IL illuminates an illumination area
32
on a reticle
12
at an even illuminance. A projection optical system
8
projects a pattern in the illumination area
32
on the reticle
12
onto a wafer
5
. In scanning exposure, the reticle
12
is moved by a reticle stage RST at a speed V
R
in a −Y direction (left direction in the plane of the drawing) with respect to the illumination area
32
. In synchronism with this movement, the wafer
5
is moved by a wafer stage WST at a speed V
W
(=&bgr;×V
R
, &bgr;: the projection magnification of the projection optical system
8
) in a +Y direction (right direction in the plane of the drawing) with respect to a projection area (exposure area similar to the illumination area
32
)
32
W defined by the projection optical system
8
. With these movements, a shot area SA on the wafer
5
is scanned in the Y direction with respect to the exposure area
32
W, as shown in
FIG. 5B
, and the pattern image on the reticle
12
is scanning-exposed on the shot area SA.
FIG. 6
is a functional block diagram showing a control system of the scanning type exposure apparatus shown in FIG.
5
A. Referring to
FIG. 6
, when a speed command signal indicating a scanning speed is input to a speed control system
61
for the wafer stage, the speed control system
61
drives the wafer stage WST in the Y direction, and performs speed control, so that the moving speed V
W
of the wafer stage WST coincides with the speed command. Normally, the position of the wafer stage WST is measured by a laser interferometer. However, in
FIG. 6
, a multiplier
66
multiplies a speed signal (a signal indicating the speed V
W
) output from the speed control system
61
by 1/&bgr;. Then, this speed signal from the multiplier
66
is supplied to an integrator
62
, and the output signal from the integrator
62
is used as a position signal indicating a position Y
W
, in the Y direction, of the wafer stage WST.
On the other hand, a speed signal (a signal indicating the speed V
R
) output from a speed control system
64
for the reticle stage is supplied to an integrator
65
, and the output signal from the integrator
65
is used as a position signal indicating a position Y
R
, in the Y direction, of the reticle stage RST. The position signals from the integrators
62
and
65
are input to a subtracter
63
, and a signal indicating a positional difference (Y
W
−Y
R
) output from the subtracter
63
is supplied to the speed control system
64
. For the sake of simplicity, the projection magnification &bgr; of the projection optical system
8
is set to be 1.
When the wafer stage WST begins to move by the speed control system
61
to follow the speed command signal, the signal which indicates the difference between the position Y
R
of the reticle stage RST and the position Y
W
of the wafer stage WST (the signal output from the subtracter
63
) changes, and is supplied to the speed control system
64
to accelerate the reticle
12
in a direction indicated by the difference. The speed control system
64
comprises a PID controller (proportional, integral, derivative controller) having an integral function, and the like, and performs acceleration control of the reticle stage RST until the above-mentioned difference (Y
W
−Y
R
) becomes zero. Thus, the reticle
12
and the wafer
5
are synchronously scanned.
In the above-mentioned prior art (FIG.
6
), the speed command signal is supplied to the speed control system
61
for the wafer stage, and the signal indicating the difference between the positions Y
W
and Y
R
of the wafer and reticle stages is supplied to the speed control system
64
for the reticle stage. Thus, after the movement of the wafer stage WST is detected, the scanning speed of the reticle stage RST is increased/decreased. For this reason, a time from acceleration of the reticle and wafer to the beginning of synchronous scanning is long.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a scanning type exposure apparatus which can shorten the time from acceleration of a mask and a substrate to the beginning of synchronous scanning for scanning exposure.
A first scanning type exposure apparatus according to the present invention, comprises an illumination system for illuminating a partial area on a mask (reticle) with light, a mask stage which is movable along a predetermined direction while holding the mask, and a substrate stage which is movable along the predetermined direction while holding a substrate. The apparatus transfers a pattern on the mask onto the substrate by synchronously driving the mask stage and the substrate stage. One of the mask stage and the substrate stage is provided with a fine movement stage which is movable relative to the one stage. The apparatus further comprises a first measuring device for measuring the position, along the predetermined direction, of the fine movement stage, a second measuring device for measuring the position, along the predetermined direction, of the other one of the mask stage and the substrate stage, a speed controller for controlling scanning speeds of the mask stage and the substrate stage, and a device for controlling the position of the fine movement stage (by a feedback method) in accordance with a difference between the position measured by the first measuring device and the position measured by the second measuring device.
As described above, according to the first apparatus of the present invention, the fine movement stage for finely adjusting the position of the mask or the substrate is arranged in addition to the mask stage and the substrate stage, which are used for moving the mask and the substrate at predetermined speeds. Since the speed controller simultaneously supplies a scanning speed command to the mask stage and
Makinouchi Susumu
Ueda Toshio
Miles & Stockbridge P.C.
Nikon Corporation
Rutledge D.
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