Photocopying – Projection printing and copying cameras – Distortion introducing or rectifying
Reexamination Certificate
1997-10-28
2001-09-25
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Distortion introducing or rectifying
C355S053000, C355S055000, C355S030000, C359S565000, C359S573000, C250S201100
Reexamination Certificate
active
06295118
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an optical arrangement and an exposure apparatus and, in another aspect, the invention is concerned with a device manufacturing method which uses such an exposure apparatus.
Semiconductor device manufacturing technology has recently advanced considerably, and fine processing techniques have also developed largely. In recent years, a major stream is to use a reduction projection exposure apparatus (stepper) having a resolution of sub-micron order to perform the fine processing. For further enhancement of resolution, many attempts such as enlargement of numerical aperture (NA) of an optical system, shortening of exposure wavelength and introduction of new optical elements, such as a diffractive optical element, for example, have been made.
FIG. 1
is a schematic view of a main portion of an exposure apparatus of a known type. Denoted in the drawing at
1
is a light source, and denoted at
2
is a reticle (mask) having a pattern formed thereon. Denoted at
3
is a reticle stage, and denoted at
4
is a barrel. Denoted at
91
is a diffractive optical element, and denoted at
5
is a lens. The barrel
4
, diffractive optical element
91
and lens
5
are components of a projection lens (optical system)
8
. Denoted at
6
is a wafer, and denoted at
7
is a wafer stage.
In operation for printing a circuit pattern on a wafer by using such an exposure apparatus, the wafer is first positioned at a desired position by means of the wafer stage
7
. Then, through focus detecting means (not shown), the position of the wafer
6
is adjusted with respect to a focus position. Subsequently, a shutter (not shown) is opened, and the reticle is illuminated with illumination light from the light source
1
. By this, the circuit pattern of the reticle is projected onto the wafer
6
through the projection lens B. The lens
5
is movable upwardly and downwardly, for correction of magnification or aberration of the projection optical system, to meet expansion of the wafer due to thermal distortion, for example.
A diffractive optical element which can be used in the exposure apparatus of
FIG. 1
may have a diameter of about 200 mm. If the diffractive optical element
91
is held on the barrel
4
in a conventional way, the diffractive optical element will distort due to gravity. It causes aberration and, thus, a change in optical characteristic of the projection lens.
Further, moving the lens upwardly and downwardly for correction of an optical characteristic of the projection lens, such as magnification or aberration, requires a complicated mechanism. The machining or assembling is not easy and, additionally, the control is not easy.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical arrangement in which distortion of a diffractive optical element due to gravity or optical characteristic of a projection lens of an exposure apparatus can be corrected easily with a simple structure.
It is another object of the present invention to provide an exposure apparatus with an optical arrangement in which distortion of a diffractive optical element due to gravity or optical characteristic of a projection lens of an exposure apparatus can be corrected easily with a simple structure.
It is a further object of the present invention to provide a device manufacturing method which uses such an exposure apparatus.
In accordance with an aspect of the present invention, there is provided an optical arrangement, comprising: a diffractive optical element; and curvature control means for changing curvature of said diffractive optical element.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: illuminating means for illuminating a mask having a pattern formed thereon; and projecting means for projecting the pattern of the mask onto a wafer, said projecting means including a diffractive optical element, and curvature control means for changing curvature of said diffractive optical element.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: printing an image of a pattern of a mask onto a wafer by use of an exposure apparatus as recited above, and developing the wafer.
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G.J. Swanson, “Binary Optics Technology: The Theory and Design of Multi-Level Diffractive Optical Elements”, Massachusetts Institute of Technology Lincoln Laboratory, Technical Report 854, Aug. 14, 1989.
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Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mathews Alan A.
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