Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2002-07-31
2003-12-16
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000
Reexamination Certificate
active
06665051
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an illumination system capable of providing uniform illumination, and more particularly relates to an exposure apparatus incorporating the illumination system, and a semiconductor device manufacturing method using same.
BACKGROUND OF THE INVENTION
Conventional exposure apparatus for manufacturing semiconductor devices include an illumination system for illuminating a circuit pattern formed on a mask and projecting this pattern through a projection optical system onto a photosensitive substrate (e.g., a wafer) coated with photosensitive material (e.g., photoresist). One type of projection optical system employs an off-axis field (e.g., an arcuate field) and projects and transfers only a portion of the mask circuit pattern onto the wafer if the exposure were static. An exemplary projection optical system having such a field comprises two reflecting mirrors, a concave mirror and a convex mirror. In such projection optical systems, transfer of the entire mask circuit pattern onto the wafer is performed dynamically by simultaneously scanning the mask and wafer in a fixed direction.
Scanning exposure has the advantage in that a high resolving power is obtained with a comparatively high throughput. In scanning-type exposure apparatus, an illumination system capable of uniformly illuminating with a fixed numerical aperture (NA) the entire arcuate field on the mask is highly desirable. Such an illumination system is disclosed in Japanese Patent Application Kokai No. Sho 60-232552. With reference to
FIG. 1
, an illumination system
10
, disclosed therein, comprises, along an optical axis A, an ultrahigh-pressure mercury lamp
12
, an elliptical mirror
14
, and an optical integrator
16
. With reference now also to
FIG. 2
, optical integrator
16
has an incident surface
16
i
, an exit surface
16
e
, and comprises a combination of four segmented cylindrical lenses
16
a
-
16
d
. Lenses
16
a
and
16
d
are located at the respective ends of optical integrator
16
, are oriented in the same direction, and have a focal length f1.
Lenses
16
b
and
16
c
are located between lenses
16
a
and
16
d
and are each oriented in the same direction, which is substantially perpendicular to the orientation of lenses
16
a
and
16
d.
Adjacent optical integrator
16
is a first condenser optical system
18
and a slit plate
20
. With reference now also to
FIG. 3
, the latter includes an arcuate aperture
20
A having a width
20
W and a cord
20
C. Adjacent slit plate
20
is a condenser optical system
22
and a mask
24
.
Mercury lamp
12
generates a light beam
26
which is condensed by elliptical mirror
14
onto incident surface
16
i
of optical integrator
16
. By virtue of having two different focal lengths, optical integrator
16
causes light beam
26
, passing therethrough, to have different numerical apertures in orthogonal directions to the beam (e.g., in the plane and out of the plane of the paper, as viewed in FIG.
1
). Light beam
26
is then condensed by condenser optical system
18
and illuminates slit plate
20
and arcuate aperture
20
A. Light beam
26
then passes therethrough and is incident condenser optical system
22
, which condenses the light beam to uniformly illuminate a portion of mask
24
.
With continuing reference to
FIG. 3
, a rectangular-shaped region
28
on slit plate
20
is illuminated so that at least arcuate aperture
20
A is irradiated. Thus, light beam
26
is transformed from a rectangular cross-section beam to an arcuate illumination beam, corresponding to aperture
20
A. Note that aperture
20
A passes only a small part of the beam incident slit plate
20
.
Generally, arcuate cord
20
C is made long to increase the size of the exposure field on the wafer. In addition, arcuate slit width
20
W is set comparatively narrow to correspond to the corrected region of the projection optical system used in combination with illumination system
10
. The illumination efficiency is determined by the ratio of surface area of arcuate aperture
20
A to rectangular-shaped region
28
. This ratio is small for illumination system
10
, an indication that the system is very inefficient, which is disadvantageous. As a result, the amount of light reaching mask
24
is fixed at a relatively low level. Since the time of exposure of mask
24
is inversely proportional to the amount of light (i.e., intensity) at the mask (i.e., the more intense the light, the shorter the exposure time), the scanning speed of the mask is limited. This limits the exposure apparatus' ability to process an increasingly large number of wafers (e.g., to increase throughput).
SUMMARY OF THE INVENTION
The present invention relates to an illumination system capable of providing uniform illumination, and more particularly relates to an exposure apparatus incorporating the illumination system, and a semiconductor device manufacturing method using same.
Accordingly, the present invention has the goals of providing an illumination system capable of supporting higher throughput with an illumination efficiency markedly higher than heretofore obtained. Another goal is to maintain uniform illumination (e.g., uniform Köhler illumination).
There has been a strong desire in recent years for a next-generation exposure apparatus capable of projecting and exposing a pattern having a much finer line width onto a photosensitive substrate by using a light source, such as a synchrotron, that supplies soft X-rays. However, prior art illumination systems are not capable of efficiently and uniformly illuminating a mask with X-ray wavelength light (“X-rays”).
Consequently, the present invention has the further goal of supplying an illumination system and exposure apparatus capable of efficiently and uniformly illuminating a mask with X-rays, and further to provide a method for manufacturing semiconductor devices using X-rays.
Accordingly, a first aspect of the invention is an illumination system for illuminating a surface over an illumination field having an arcuate shape. The system comprises a light source for providing a light beam and an optical integrator. The optical integrator includes a first reflective element group having an array of first optical elements each having an arcuate profile corresponding to the arcuate shape of the illumination field. Each first optical element also includes an eccentric reflecting surface comprising an off-axis section of a spherical reflecting surface or an off-axis section of an aspherical reflecting surface. The array of first optical elements is designed so as to form a plurality of arcuate light beams capable of forming multiple light source images. The illumination system further includes a condenser optical system designed so as to condense the plurality of arcuate light beams to illuminate the surface over the arcuate illumination field in an overlapping manner.
A second aspect of the invention is the illumination system as described above, wherein the condenser optical system comprises a condenser mirror with a focal point, with the condenser mirror arranged such that the focal point substantially coincides with the surface to be illuminated.
A third aspect of the invention is an illumination optical system as described above, further comprising a second reflective element group having a plurality of second optical elements. Each of the second optical elements has a rectangular shape and a predetermined second reflecting curved surface which is preferably an on-axis section of a spherical or aspherical reflective surface. The first and second reflecting element groups are opposingly arranged such that the multiple light source images are formed at the plurality of second optical elements when the light beam is incident the first reflecting element group.
A fourth aspect of the invention is an exposure apparatus for exposing the image of a mask onto a photosensitive substrate. The apparatus comprises the illumination system as described above, a mask stage capable of supporting the mask, and a substrate s
Fuller Rodney
Nikon Corporation
Oliff & Berridg,e PLC
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