Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
1999-09-17
2001-01-09
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S858000, C359S857000, C359S364000, C359S365000
Reexamination Certificate
active
06172825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a catoptric reduction projection optical system and projection exposure apparatus and methods using same, for photolithographically manufacturing devices like semiconductor devices, liquid crystal display devices, thin film magnetic heads and the like.
BACKGROUND OF THE INVENTION
With the advance in recent years of microminiaturization in the manufacture of semiconductor devices and semiconductor chip mounting boards, there have beer increasing demands for higher resolving power in the exposure apparatus used to manufacture these items. To satisfy this demand, the wavelength of the light source of the apparatus must be shortened and/or the NA (numerical aperture) of the projection optical system of the apparatus must be increased. If the wavelength is shortened, the optical glasses that can withstand practical use is limited due to the absorption of light. Furthermore, when it comes to the short wavelengths of ultraviolet rays and X-rays, usable optical glasses are nonexistent. In this case, it is impossible to construct reduction projection optical systems that are dioptric or catadioptric.
A reduction catoptric projection optical system is disclosed in, for example, U.S. Pat. No. 5,815,310. The projection optical system disclosed therein includes two sets of reduction optical systems comprising reflective surfaces with a concave-convex-concave configuration, and forms an intermediate image between the two reduction optical systems. This projection optical system has the advantage that its six reflective surfaces increase the number of degrees of freedom for aberration correction. Further, a plane reflective mirror is not needed just for the return path, since the number of reflective surfaces is naturally even. In addition, since the reduction magnification of the entire optical system can be distributed among the reduction optical systems, it has the advantage that the burden of each reduction optical system can be lightened. Unfortunately, however, because the two reduction optical systems are joined by a pair of mirror pairs, the diameter of the mirror pairs unavoidably increases. This results in increased cost of the projection optical system.
SUMMARY OF THE INVENTION
The present invention relates to a catoptric reduction projection optical system and projection exposure apparatus and methods using same, for photolithographically manufacturing devices like semiconductor devices, liquid crystal display devices, thin film magnetic heads and the like.
The present invention has the goal to obtain excellent imaging performance while keeping the diameter of the reflective mirrors small, even with on the order of six reflective surfaces. In the present invention, the word “light” refers generally to electromagnetic radiation including the wavelength range from the visible down to x-ray.
Accordingly, a first aspect of the invention is a catoptric reduction projection optical system capable of forming a reduced magnification image of an object present on a first surface onto a third surface. The system comprises first and second catoptric optical systems. The first catoptric optical system is capable of forming an intermediate image of the object onto a second surface, and comprises a first mirror pair having a first reflective mirror and a second reflective mirror. The second catoptric optical system is capable of imaging the intermediate image formed on the second surface onto the third surface, and comprises a second mirror pair having a third reflective mirror with a concave reflective surface and a fourth reflective mirror with a reflective surface of a predetermined shape, and a third mirror pair having a fifth reflective mirror with a convex reflective surface and a sixth reflective mirror with a concave reflective surface. The light from the first surface forms the intermediate image on the second surface after reflecting from the first mirror pair. Then, the light from the intermediate image is reflected by the second mirror pair in the order of the third reflective mirror and the fourth reflective mirror. Then, the light reflected by the second mirror pair is further reflected by the third mirror pair in the order of the fifth reflective mirror and the sixth reflective mirror, and is then guided to the third surface.
A second aspect of the invention is the catoptric reduction projection optical system as described above, further satisfying the following condition:
−0.005<(
p
1
+
p
2
+
p
3
+
p
4
+p
5
+
p
6
)<0.005
wherein p
1
is a paraxial curvature of the first reflective mirror, p
2
is a paraxial curvature of the second reflective mirror, p
3
is a paraxial curvature of the third reflective mirror, p
4
is a paraxial curvature of the fourth reflective mirror, p
5
is a paraxial curvature of the fifth reflective mirror, and p
6
is a paraxial curvature of the sixth reflective mirror.
A third aspect of the invention is a projection exposure apparatus for exposing a photosensitive substrate with an image of a reticle. The apparatus comprises an illumination optical system that guides exposure light having an exposure wavelength to the reticle, and the projection optical system as described above. The latter is arranged to receive the exposure light from the reticle to form a reduced image of the reticle and exposing the image onto the photosensitive substrate. The exposure is performed while moving the reticle and the photosensitive substrate relative to the catoptric reduction projection optical system.
A fourth aspect of the invention is a method of exposing a photosensitive substrate with a reduced image of a reticle. The method comprising the steps of first, providing the projection exposure apparatus as described above, then guiding light from the illumination optical system to the reticle, and then forming a reduced image of the reticle onto the photosensitive substrate with the projection exposure apparatus while scanning the reticle and the photosensitive substrate relative to the projection exposure apparatus.
REFERENCES:
patent: 4693569 (1987-09-01), Offner
patent: 5686728 (1997-11-01), Shafer
patent: 5805365 (1998-09-01), Sweatt
patent: 5815310 (1998-09-01), Williamson
Nikon Corporation
Oliff & Berridg,e PLC
Sikd-er Mohammad Y.
Spyrou Cassandra
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