Optical: systems and elements – Lens – With reflecting element
Reissue Patent
2001-01-19
2004-02-24
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With reflecting element
C359S720000
Reissue Patent
active
RE038438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catadioptric reduction optical system suitably applied to a projection optical system for reduction projection in a projection exposure apparatus of a one-shot exposure method or a scanning exposure method, used to manufacture a semiconductor element or a liquid crystal display element in a photolithographic process and, more particularly, to a catadioptric reduction projection optical system having a magnification of about 1/4 to 1/5 with a resolution on the submicron order in the ultraviolet wavelength range.
2. Related Background Art
In fabricating semiconductor devices or liquid crystal display devices, etc. by photolithography process, the projection exposure apparatus is used for demagnifying through a projection optical system a pattern image on a reticle (or photomask, etc.) for example at a ratio of about 1/4 to 1/5 to effect exposure of the image on a wafer (or glass plate, etc.) coated with a photoresist and the like.
With the recent increase in the integration degree of semiconductor elements and the like, a higher resolution is required for a projection optical system used in a projection exposure apparatus. In order to meet this requirement, the wavelength of illumination light (exposure wavelength) for exposure must be shortened, or the numerical aperture (NA) of the projection optical system must be increased. If, however, the exposure wavelength is shortened, the types of optical glass which can be used in practice are limited because of the absorption of illumination light. In particular, as the exposure wavelength becomes 300 nm or less, only synthetic quartz and fluorite can be used in practice as glass materials.
The difference between the Abbe constants of the synthetic quartz and the fluorite is not large enough to correct chromatic aberration. For this reason, if the exposure wavelength becomes 300 nm or less, and a projection optical system is constituted by only a refracting optical system, chromatic aberration correction is very difficult to perform. In addition, since fluorite undergoes a considerable change in refractive index with a change in temperature, i.e., has poor temperature characteristics, and involves many problems in a lens polishing process, fluorite cannot be used for many portions. It is, therefore, very difficult to form a projection optical system having a required solution by using only a refracting system.
In contrast to this, attempts have been made to form a projection optical system by using only a reflecting system. In this case, however, the projection optical system increases in size and requires aspherical reflecting surfaces. It is very difficult to manufacture large, high-precision, aspherical surfaces
Under the circumstances, various techniques have been proposed to form a reduction projection optical system by using a so-called catadioptric optical system constituted by a combination of a reflecting system and a refracting system consisting of optical glass usable in relating to the exposure wavelength to be used. As an example, a reduction projection exposure apparatus including a catadioptric projection optical system having a beam splitter constituted by a cubic prism and serving to project a reticle image entirely by using a light beam near the optical axis is disclosed in, e.g., U.S. Pat. Nos. 4,953,960, 5,220,454, 5,089,913, or 5,402,267.
SUMMARY OF THE INVENTION
The present invention has as its object to provide a catadioptric reduction projection optical system which can use a beam splitting optical system smaller in size than a conventional polarizing beam splitter, can set a long optical path from a concave reflecting mirror to the image plane, can easily adjust the optical system, and has excellent imaging performance.
It is another object of the present invention to provide a catadioptric reduction projection optical system which can reduce the size of a beam splitting optical system such as a polarizing beam splitter and still has a space in which an aperture stop can be arranged.
It is still another object of the present invention to provide a catadioptric reduction projection optical system which uses a compact beam splitting optical system and can be applied to a projection optical apparatus of the scanning exposure scheme.
The catadioptric reduction projection optical system can be applied to a projection exposure apparatus of a scanning exposure method, based on use of a compact beam splitting means such as a polarizing beam splitter and the like. Besides a projection exposure apparatus of a one-shot exposure method, the catadioptric reduction projection optical system can be also applied to a recent apparatus employing a scanning exposure method such as the slit scan method or the step-and-scan method, etc. for effecting exposure while relatively scanning a reticle and a wafer to a projection optical system.
To achieve the above objects, as shown in
FIGS. 1 and 2
. an projection exposure apparatus of the present invention comprises at least a wafer stage
3
being movable and allowing photosensitive substrate W to be held on a main surface thereof, an illumination optical system
1
for emitting exposure light of a predetermined wavelength and transferring a predetermined pattern of a mask (reticle R) onto the substrate W, and a catadioptric reduction projection optical system
5
provided between a first surface P
1
on which the mask R is disposed and a second surface P
2
on which a surface of the substrate W is corresponded, for projecting an image of the pattern of the mask R onto the substrate W. The illumination optical system
1
includes an alignment optical system
110
for adjusting a relative positions between the mask R and the substrate W, and the mask R is disposed on a reticle stage
2
which is movable in parallel with respect to the main surface of the wafer stage
3
. The catacioptric reduction projection optical system has a space permitting an aperture stop
6
to be set therein. The sensitive substrate W comprises a wafer
8
such as a silicon wafer or a glass plate, etc., and a photosensitive material
7
such as a photoresist and the like coating a surface of the wafer
8
.
In particular, the catadioptric reduction projection optical system, as shown in
FIGS. 3 and 4
, includes at least a first imaging optical system having a focal length f
1
(refracting lens group
or first dioptric imaging optical sub-
system
G
1
(f
1
)) having a positive refractive power and for forming a first intermediate
(
i.e., primary
)
image
9
as a reduced image of the pattern on the object plane P
1
, beam splitting means
10
for splitting at least part of a light beam from the first imaging optical system, a second imaging optical system having a focal length f
2
(catadioptric lens group
or catadioptric imaging optical sub-
system
G
2
(f
2
)) including a concave reflecting mirror M
1
for reflecting a light beam split by the beam splitting means, and for forming a second intermediate
(
i.e., secondary
)
image
12
as an image of the first intermediate image
9
, and a third imaging optical system having a focal length f
3
(refracting lens group
or second dioptric imaging optical sub-
system
G
3
(f
3
)) for forming a third intermediate image (a final image) as an image of the second intermediate image
12
on the image plane P
2
on the basis of a light beam, of a light beam from the second imaging optical system, which is split by the beam splitting means
10
.
Since the first imaging optical system G
1
(f
1
) forms a first reduced intermediate image in an optical path from the image plane P
1
to the concave reflecting mirror M
1
(or M
2
), the beam splitting means can exactly carry out the splitting of a light beam from the first imaging optical system G
1
(f
1
). Since the second imaging optical system G
2
(f
2
) forms a second intermediate image in an optical path from the concave reflecting mirror M
1
(or M
2
) to the third imaging optical system G
3
(f
3
), a smaller beam splitting mean
Nikon Corporation
Sugarman Scott J.
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