Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1998-12-11
2001-11-13
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C356S400000, C356S401000
Reexamination Certificate
active
06317196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus, and more particularly, to a projection exposure apparatus in which a pattern on a mask is projected onto a photosensitive substrate and exposed by moving the mask and the photosensitive substrate in a predetermined direction with respect to a projection optical system.
2. Discussion of the Related Art
FIG. 7
illustrates the construction of a conventional projection exposure apparatus. A pattern on a mask
110
is projected onto a glass plate
114
(photosensitive substrate) at equal magnification via a projection optical system
112
. In
FIG. 7
, the direction of movement (scan) of the mask
110
and glass plate
114
is taken as the X axis, a direction perpendicular to the X-axis in the plane of the mask
110
is taken as the Y-axis, and a direction normal to the mask
110
(i. e., the direction of the optical axis of the projection optical system
112
) is taken as the Z-axis. The projection optical system
112
is installed at the center of a C-shaped bridge
116
(fixed support). An illumination optical system
118
includes a light source, such as an ultra-high-pressure mercury lamp, and a fly-eye lens, etc., and is installed on one end of the bridge
116
to illuminate a predetermined portion of the mask
110
with uniform brightness.
The mask
110
and the glass plate
114
are held on a mask stage
120
and a plate stage
122
, respectively, such that the mask
110
and the glass plate
114
are substantially parallel to the XY plane. Furthermore, mask stage
120
and plate stage
122
are installed on a carriage
124
as an integral unit. Two Y-direction micromotion actuators
126
and
128
are installed on the carriage
124
beneath the mask stage
120
to adjust the position of the mask stage
120
in the Y direction. An X-direction micromotion actuator
130
is installed on the carriage
124
at the end portion of the mask stage
120
on the side of the projection optical system
112
to adjust the position of the mask stage
120
in the X direction.
The plate stage
122
is constructed in such a way as to be movable in the Z direction and tiltable about the X-axis and the Y-axis in order to substantially match the exposed region on the plate
114
with the pattern imaging plane of the mask
110
formed through the projection optical system
112
during scanning exposure. In other words, the imaging condition is adjusted by moving the plate stage
122
in the Z direction and by adjusting inclination of the glass plate
114
(i.e., tilting the glass plate
114
about the X-axis and the Y-axis). By performing such adjustments, it is possible to make corrections for thickness irregularities, inclination, and deformation, etc., which exist in the glass plate
114
.
The carriage
124
can slide in the X direction along guide members
132
a
and
132
b
. When the carriage
124
is moved in the X direction with respect to illuminating light emitted by the illumination system
118
, the mask
110
and the glass plate
114
are synchronously scanned by the illumination light from the projection optical system
112
. This way, the pattern on the mask
110
is successively transferred onto the glass plate
114
. Thus, the entire pattern on the mask
110
is projected and exposed onto the glass plate
114
by one scanning operation.
Next, an alignment mechanism for aligning the mask
110
with the glass plate
114
in the abovementioned projection exposure apparatus will be described. Moving mirrors
136
a
,
136
b
,
138
a
, and
138
b
are fixed to bottom portions of the mask stage
120
and plate stage
122
in respective positions corresponding to the Y-direction micromotion actuators
126
and
128
. The moving mirrors
136
a
and
136
b
are arranged to reflect laser beams originating from a differential type laser interferometer
140
fixed to the carriage
124
. More specifically, a laser beam emitted by the laser interferometer
140
is split into two laser beams by a split optical system
144
, and the resultant two laser beams are guided to the moving mirrors
136
a
and
136
b
. The laser beams reflected by the moving mirrors
136
a
and
136
b
return to the laser interferometer
140
through the split optical system
144
. At the interferometer
140
, the two light beams reflected by the moving mirrors
136
a
and
136
b
are coupled to produce interference. Based on the interference information, the relative positional deviation between the mask
110
and the glass plate
114
in the non-scanning direction (i.e., the Y direction) is detected at a position corresponding to Y-direction micromotion actuator
126
.
The moving mirrors
138
a
and
138
b
are arranged to reflect laser beams originating from a differential type laser interferometer
142
fixed to the carriage
124
. More specifically, a laser beam emitted by the laser interferometer
142
is split into two laser beams by a split optical system
146
, and the resultant laser beams are guided to the moving mirrors
138
a
and
138
b
. The laser beams reflected by the moving mirrors
138
a
and
138
b
return to the laser interferometer
142
through the split optical system
146
. At the interferometer
142
, the two light beams reflected by the moving mirrors
138
a
and
138
b
are coupled to produce interference. Based on the interference information, the relative positional deviation between the mask
110
and the glass plate
114
in the non-scanning direction (i.e., the Y direction) is detected at a position corresponding to Y-direction micromotion actuator
128
.
Thus, the relative positional deviation between the mask
110
and the glass plate
114
in the Y direction can be detected by the laser interferometer
140
and the laser interferometer
142
at two points
126
,
128
, which are separated by a predetermined distance in the X direction. Furthermore, the relative rotational deviation about the Z direction between the mask
110
and the glass plate
114
can be detected from the difference in the results detected at the laser interferometer
140
and laser interferometer
142
. When such deviations are detected, the Y-direction micromotion actuators
126
,
128
are driven to offset the deviations. Furthermore, since the laser interferometers
140
and
142
utilize laser beams from light sources fixed to the carriage
124
, the relative positional deviation detected in the Y direction is unaffected by changes in the attitude of the carriage
124
. For example, even when the carriage
124
is displaced in the Y direction due to fluctuations in the X direction movement of the carriage
124
, the light sources for the laser interferometers
140
and
142
and the split optical systems
144
and
146
are also displaced together with the carriage
124
. Accordingly, no positional deviations between the mask
110
and glass plate
114
are detected in the Y direction.
A reflex mirror
148
and a reflex mirror
150
are disposed on the end portions of the mask stage
120
and plate stage
122
, respectively, on the negative X direction side in the positions corresponding to the X-direction micromotion actuator
130
. The reflex mirrors
148
and
150
are arranged to reflect laser beams from laser interferometers
152
and
154
, respectively. The laser interferometer
152
is a length measuring type interferometer, and emits a laser beam from a light source toward the reflex mirror
148
fixed to the mask stage
120
and toward a fixed mirror (not shown in the figures) fixed to the bridge
116
. Furthermore, this interferometer
152
detects interference (synthesis) between the laser beam reflected by the reflex mirror
148
and the laser beam reflected by the fixed mirror, and determines the position of the mask
110
in the X direction on the basis of the interference.
The laser interferometer
154
is also a length measuring type interferometer, and emits a laser beam from a light source fixed to a fixed system, such as the bridge
116
or the projection optical system
112
, to
Hamada Tomohide
Kakizaki Yukio
Kats Kinya
Shirasu Hiroshi
Adams Russell
Fuller Rodney
Morgan & Lewis & Bockius, LLP
Nikon Corporation
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