Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1998-12-28
2001-09-04
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C355S071000, C356S400000
Reexamination Certificate
active
06285437
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for controlling stages and an apparatus therefor, in particular, it relates to a method for controlling stages and an apparatus therefor preferable to be used for so-called scanning type exposure apparatuses, in which a pattern on a mask is transferred onto a photosensitive substrate while moving a mask stage and a substrate stage in synchronization in predetermined scanning directions respectively, and it also relates to a scanning type exposure apparatus provided therewith.
DESCRIPTION OF THE RELATED ART
Recently, an exposure method of the slit scan system has been developed, in which a photosensitive substrate is successively exposed with a pattern on a reticle by illuminating a part of a pattern area on a mask (reticle) in a shape of slit or a shape of circular arc, scanning the reticle with respect to the illuminated area, and scanning the photosensitive substrate in synchronization with the scanning for the reticle with respect to an area (exposure area) conjugate with the illuminated area relative to a projection optical system. A scanning type exposure apparatus which adopts this system has an advantage that a projected image is prevented from distortion, and illuminance can be easily made uniform because the illumination area on the reticle is smaller than that of an exposure apparatus of the full-wafer exposure system, for example, of the step-and-repeat system, and only a part of an image field of the projection optical system is used for exposure. Such a scanning type exposure apparatus is provided with a substrate stage on which the substrate is placed, and a reticle stage (mask stage) on which the reticle is placed. During scanning exposure, it is necessary to make control so that the both stages are simultaneously accelerated in opposite directions or in an identical direction, and each of velocities of the stages after completion of the acceleration is synchronized.
FIG. 4
schematically shows an example of arrangement of a system for controlling stages of a conventional scanning type projection exposure apparatus used in semiconductor production steps.
In this scanning type exposure apparatus, a laser interferometer
70
for wafer and a laser interferometer
72
for reticle are used to detect positions of a wafer stage (substrate stage)
74
and a reticle stage (mask stage)
76
respectively, and these stages
74
,
76
are simultaneously subjected to velocity control. As shown in
FIG. 4
, a positional error between the both stages
74
,
76
, which is obtained from outputs of the both interferometers
70
,
72
, is sent in a feedback manner to one of velocity-instructing units for any of the stages, for example, to a velocity-instructing unit
78
for the reticle stage
76
. The velocity-instructing unit
78
gives a velocity command to cancel an amount corresponding to the error to a velocity control unit
80
for the reticle stage
76
. Thus the velocity control unit
80
performs velocity control for the reticle stage
76
on the basis of the velocity command and a velocity (detected value) of the reticle stage
76
obtained from the output of the laser interferometer
72
.
In the conventional method for controlling stages described above, adjustment was performed by allowing the position of the reticle stage
76
to follow the position of the wafer stage
74
. However, there has been an inconvenience that the response of the reticle stage
76
is delayed because the reticle stage
76
has a large weight. In addition, a vibration occurs on a vibration-preventive pedestal
82
on which the stages
74
,
76
are placed resulting from a difference (M
1
a
1
-M
2
a
2
) between reaction forces of thrusts applied to the stages
74
,
76
because the stages
74
,
76
having large masses are subjected to scanning (M
1
and M
2
represent masses of the mask stage and the reticle stage respectively, and a
1
and a
2
represent accelerations during driving of the mask stage and the reticle stage respectively). Resulting from the vibration, fixed mirrors
84
,
86
for each of the laser interferometers vibrate. In this situation, no problem arises if the fixed mirrors
84
vibrates identically to the fixed mirror
86
. However, actually, the transfer function from the vibration-preventive pedestal
82
to each of the fixed mirrors
84
,
86
is different, and hence, for example, the amplitude is different. For this reason, the positional error, which is a difference between measured values obtained by the interferometers
70
,
72
, includes an amount of an error resulting from the vibrations of the fixed mirrors
84
,
86
. Such a positional error is subjected to the feedback control as described above, on the basis of which the velocity control (positional control) is performed for the reticle stage
76
. Accordingly, when the vibration is settled, the reticle stage
76
is discrepant with an original target position. Therefore, there has been an inconvenience that it takes time for the both stage to move to their original target positions and provide a desired synchronized state.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a method for controlling stages in which the inconvenience possessed by the conventional art as described above is dissolved, and the time required to regulate and establish synchronization between a substrate stage and a mask stage can be shortened.
A second object of the present invention is to provide an apparatus for controlling stages and a scanning type exposure apparatus provided therewith in which the time required to regulate and establish synchronization between a substrate stage and a mask stage can be shortened.
A third object of the present invention is to improve accuracy of synchronization between a substrate (a substrate state) and a mask (a mask stage).
According to a first aspect of the present invention, there is provided a method for controlling stages for an exposure apparatus comprising a mask stage for holding a mask, which is movable in a predetermined scanning direction, a substrate stage for holding a photosensitive substrate, which is movable in the scanning direction in synchronization with the mask stage, and a vibration-preventive pedestal for supporting the substrate stage, said method comprising:
making synchronized movement of the mask stage and the substrate stage in the predetermined scanning direction for scanning exposure;
detecting, during the synchronized movement, a positional discrepancy amount between the both stages, and calculating a vibration amount of the vibration-preventive pedestal; and
controlling the movement of the both stages such that the positional discrepancy between the both stages is corrected on the basis of the detected positional discrepancy amount and the calculated vibration amount.
According to a second aspect of the present invention, there is provided a scanning type exposure method for an exposure apparatus comprising a mask stage for holding a mask, which is movable in a predetermined scanning direction, a substrate stage for holding a photosensitive substrate, which is movable in the scanning direction in synchronization with the mask stage, and a vibration-preventive pedestal for supporting the substrate stage, said method comprising:
irradiating the mask with illumination light;
performing exposure for the photosensitive substrate with a pattern on the mask by making synchronized movement of the mask stage and the substrate stage in the predetermined scanning direction;
detecting, during the synchronized movement of the mask stage and the substrate stage, a positional discrepancy amount between the both stages, and calculating a vibration amount of the vibration-preventive pedestal; and
controlling the movement of the both stages such that positional discrepancy between the both stages is corrected on the basis of the detected positional discrepancy amount and the calculated vibration amount.
In the scanning type exposure apparatus, positions of the substrate stage and the mas
Brown Khaled
Mathews Alan A.
Nikon Corporation
Oliff & Berridg,e PLC
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