Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-11-29
2004-09-07
Kim, Peter B. (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S053000, C356S401000
Reexamination Certificate
active
06788393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stage unit and an exposure apparatus. More particularly, it relates to an exposure apparatus that performs exposure on a substrate with an energy beam so as to form a predetermined pattern on the substrate and a stage unit that can be suitably applied to the exposure apparatus.
2. Description of the Related Art
Conventionally, in a lithographic process to manufacture devices such as a semiconductor device or a liquid crystal display device and the like, an exposure apparatus is used that transfers a pattern formed on a mask or a reticle (hereinafter generally referred to as a “reticle”) onto a wafer or a glass plate (hereinafter generally referred to as a “wafer”) via a projection optical system. In recent years, due to higher integration of the semiconductor device, the type of projection exposure apparatus that moves step by step such as the reduction projection exposure apparatus based on the step-and-repeat method (the so-called stepper) and the scanning type projection exposure apparatus, which is an improvement of the stepper, based on the step-and-scan method (the so-called scanning stepper) or the like has become mainstream.
The semiconductor device or the like is made by overlaying patterns in multiple layers, therefore, with the exposure apparatus such as the stepper the overlay of the pattern formed on the reticle onto the pattern already formed on the wafer needs to be highly accurate. This requires a precise measurement of the position on the wafer of the shot area where the pattern is formed, and for the precise measurement a method that uses a variety of position measurement sensors to measure the position of alignment marks arranged along each shot area is employed.
Furthermore, for this measurement, as a reference for measuring the positional relationship between the reticle, the projection lens, and the wafer a fiducial mark plate on which various types of fiducial marks are formed is arranged in the vicinity of the wafer on the wafer stage that holds the wafer.
Normally, one fiducial mark plate is arranged on the wafer stage, and by measuring the fiducial marks formed on the fiducial mark plate the relative distance between position measurement sensors is controlled as well as the orthogonal degree of the stage interferometer that measures the position of the stage and the conversion rate used to figure out the distance from the interference fringe count measured with the stage interferometer.
In the case, however, when measurements for these controls are performed using a single fiducial mark plate, the measurement accuracy may decrease since the span of the measurement distance is limited by the size of the fiducial mark plate.
Therefore, as a means of improving the measurement accuracy, the possibility of increasing the size of the fiducial mark plate can be considered, however, this may lead to a larger stage size. Especially, with the exposure apparatus recently gathering attention that comprises a plurality of substrate stages, since the stages require an extremely large driving range the footprint of the apparatus naturally has to increase, thus causing an inconvenience.
Furthermore, with the exposure apparatus comprising a plurality of substrate stages as is referred to above, in most cases the exposure apparatus comprises only one optical system for exposure, and in such a case there is a tendency of the exposure position and the alignment position being far apart so as to prevent interference between stages from occurring. This makes the optical axis of the interferometer measuring the position of the stage between the exposure position and the alignment position stray from the stage, nevertheless, even in such a case, the positional relationship of the substrate on the stage with respect to the optical system for exposure and the mask must be controlled with good accuracy.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the circumstances described above, and has as its first object to provide a stage unit that can be downsized while maintaining its measurement performance.
It is the second object of the present invention to provide an exposure apparatus which substrate stage can be downsized as well as the footprint of the apparatus reduced.
And, it is the third object of the present invention to provide an exposure apparatus which substrate stage can be downsized and the footprint of the apparatus reduced, and is also capable of controlling the position of the substrate with good accuracy at all times.
According to the first aspect of the present invention, there is provided a stage unit comprising: a substrate holding member which holds a substrate; and a substrate stage which moves two dimensionally with the substrate holding member mounted, and on which a plurality of fiducial marks are arranged dispersed by each measurement sequence which uses the fiducial marks with a positional relationship between each of said fiducial marks and the substrate holding member constant.
With this stage unit, a plurality of fiducial marks are arranged dispersed by each measurement sequence which uses the fiducial marks and the positional relationship between each of the fiducial marks and the substrate holding member is constant. Therefore, for example, the fiducial marks can be respectively arranged apart at a certain interval on the periphery of the substrate holding member. This makes it possible to sufficiently secure the interval (distance) between the fiducial marks, relax the limitations on the measurement span, and consequently, improve the measurement accuracy. In addition, the respective fiducial marks can be arranged on the substrate stage even when the space is small. Since the plurality of fiducial marks are arranged dispersed by each measurement sequence which uses the fiducial marks, the performance regarding measurement can be maintained. Accordingly, the stage can be downsized, maintaining its measurement performance.
In this case, the plurality of fiducial marks can be at least three fiducial marks respectively arranged in the vicinity of each vertex position of a polygon, which contains a center of the substrate holding member. In such a case, the center of the substrate holding member lies within the area of the polygon surrounded by the fiducial marks, therefore, in the case of obtaining the center of the substrate holding member based on the measurement results of the position of the fiducial marks, the central point corresponds, so to speak, to the interpolation point of the fiducial mark positions. Accordingly, by performing a predetermined calculation based on the positional information on the fiducial marks, the holding member coordinate system which origin is the center of the substrate holding member can be obtained with a sufficient level of reliability.
With the stage unit according to the present invention, the plurality of fiducial marks can include a first fiducial mark and a second fiducial mark, which are arranged on a straight line passing through a center of the substrate holding member on opposite sides with respect to the center. In such a case, since the first fiducial mark and the second fiducial mark are arranged on a straight line passing through the center of the substrate holding member on opposite sides with respect to the center, the interval between both fiducial marks can be around the diameter length of the substrate holding member, which relaxes the limitations on the measurement span, and consequently, the measurement accuracy can be improved. In addition, since the two fiducial marks are symmetric with respect to the center of the substrate holding member, it is possible, for example, to easily calculate the center coordinate and the rotational angle of the substrate holding member.
With the stage unit according to the present invention, each fiducial marks may be formed directly on the substrate stage, however, the stage unit may further comprise: a plurality of fiducial mark plates arr
Kim Peter B.
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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