Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2003-08-27
2004-07-13
Kim, Peter B. (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S053000, C355S077000, C356S399000
Reexamination Certificate
active
06762826
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a substrate attracting and holding system for grasping a substrate or workpiece and, more particularly, to a substrate attracting and holding system for use in a semiconductor manufacturing apparatus, a liquid crystal substrate manufacturing apparatus, a magnetic head manufacturing apparatus, a semiconductor inspection apparatus, a liquid crystal inspection apparatus, or a magnetic head inspection apparatus or for use in manufacture of a micro-machine, for example. In another aspect, the invention concerns an exposure apparatus or a device manufacturing method using such a substrate attracting and holding system.
In reduction projection exposure apparatuses used in the manufacture of semiconductor devices, for example, enlargement of the numerical aperture (NA) has been promoted to meet miniaturization of a device (chip). Although the resolution is improved by a larger numerical aperture, the effective depth of focus is shortened on the other hand. Thus, in order to maintain the resolution while keeping a sufficient practical depth, attempts have been made reduce the curvature of image field of a projection optical system or to improve the wafer flatness in regard to wafer thickness non-uniformness or flatness precision of a chuck.
One factor for causing degradation of the flatness of a wafer surface is the presence of a foreign particle caught between a chuck and a wafer. If a foreign particle of a few microns is once caught therebetween, the wafer at that portion is deformed and raised thereby. Where the effective depth of focus is 1 micron or less, local defocus occurs there and, in a worst case, a pattern defect is produced. In order to avoid degradation of the product yield rate due to such foreign particles, based on the probability, pin contact chucks (pin chucks) wherein the contact rate between a chuck and a wafer is reduced to a minimum are used prevalently.
As regards a machine for processing a substrate such as a semiconductor wafer, for semiconductor device manufacture, or a liquid crystal substrate, for liquid crystal display device manufacture, for example, a projection exposure apparatus, generally it uses a substrate attracting and holding system based on a vacuum attraction force to hold and secure a substrate (workpiece) and to correct any warp thereof to keep its flatness.
FIG. 31
shows an example of such substrate attracting and holding system. In the substrate attracting and holding system (chuck)
201
illustrated, a substrate carrying plane is defined by a carrying table which comprises a plurality of pin contact type protrusions
202
disposed in a grid and a peripheral rim type protrusion
203
provided at the peripheral portion of the carrying plane for supporting the peripheral portion of a substrate. Also, there are suction holes
205
formed at the carrying plane where the contact type protrusions are provided, which holes are communicated with a vacuum piping system for reducing the pressure between the carrying plane and a substrate to be carried thereon.
The substrate attracting and holding system of a structure such as described above is used in a semiconductor exposure apparatus, for example. A wafer which is a substrate is conveyed onto the chuck
201
by means of a conveying system. After the wafer is placed on the chuck
201
, it is held fixed on the chuck
201
by vacuum attraction applied through the attraction holes
205
. Here, in order to reduce the probability of occurrence of deformation of the wafer surface due to catching a foreign particle between the chuck carrying table and the wafer, the total area of the substrate supporting protrusions distributed along the carrying plane is made small.
In the substrate attracting and holding system such as described above, the layout of the substrate supporting protrusions which provide the chuck carrying table is determined without any specific concern to the processing region on the substrate. It is set without any positional relationship with the substrate processing region. Namely, if the substrate processing region changes, the same chuck is used continuously. Therefore, if the surface of a substrate is deformed as a result of the attraction and holding of the substrate, the deformation may cause not only a deformation of that portion of the substrate in a vertical direction but also a distortion along the plane of the substrate. Further, the layout of the substrate supporting protrusions of the chuck is determined without any specific concern to the layout of alignment marks of a substrate. If the alignment mark layout of the substrate changes, the same chuck is used continuously. While a deformation of the substrate surface resulting from the attraction and holding of the substrate may cause an error in the coordinate of an alignment mark, since the relationship between each substrate alignment marks and each substrate supporting protrusions of the chuck is unknown, it is not possible to correct the coordinate error and, therefore, the registration precision is degraded.
On the other hand, in a lithographic process among semiconductor manufacturing processes in which a very fine pattern is transferred by exposure, in consideration of the depth of focus being decreased with miniaturization of the device or a coordinate error of a pattern to be transferred, the flatness of a substrate as held by a chuck has to be decreased as much as possible. If the substrate has a distortion along a horizontal direction caused by the deformation of the substrate surface, the error in the coordinate of an alignment mark of the substrate becomes large as a result of it. Additionally, if such coordinate error is different in each region (hereinafter, “shot”) to be processed by a single operation or in each semiconductor device (hereinafter, “die”), since a semiconductor device is produced by superposing various patterns, the pattern registration is much degraded. If there is a large difference between shots, it can not be corrected easily and, in a worst case, a defect of a semiconductor device is produced.
It is known that, in a pin chuck, a wafer is deformed and warped between pins of the chuck due to vacuum attraction and that this causes degradation of the flatness of the wafer surface. Many proposals have been made to solve this problem. For example, Japanese Patent No. 2574818 proposes a structure wherein a ring-like groove is formed in an outer peripheral portion of a chuck and wherein pins are provided in a central portion, inside the groove, at a pin pitch of 2 mm or less, so as to keep good wafer flatness at the chuck peripheral portion and good wafer flatness within the pin pitch at the chuck central portion. In this patent, it is stated that, with a pin chuck having pins disposed in a grid, the flatness within the pin pitch can be approximated by a model of a beam having both ends free-supported and that, from a desired flatness, a required pin pitch can be made 2 mm or less. However, the approximation with the beam having both ends free-supported means that the pin pitch as a whole is determined by using the condition for the support with the free end at the outer peripheral portion which condition is worse than that at the central portion. There is no disclosure about determining optimum pin pitches for the flatness at the outer peripheral portion and at the central portion, respectively. Therefore, this causes an inconvenience that the pin pitch at the central portion becomes smaller than as required and, as a result, the contact rate becomes larger than as required.
In an attempt to solving this problem, Japanese Patent No. 2821678 proposes a structure wherein the pin pitch at a central portion of a chuck is made larger than that at an outer peripheral portion of the chuck, thereby to improve the wafer flatness at the chuck outer peripheral portion and the chuck central portion while keeping the contact rate small. According to this proposal, it is suggested that the flatness within the pin pitch at the peripheral portio
Fujita Itaru
Nogawa Hideki
Takabayashi Yukio
Tsukamoto Izumi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Kim Peter B.
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