Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2002-01-15
2004-11-16
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C362S268000
Reexamination Certificate
active
06819493
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to projection exposure apparatuses and device fabrication methods using these apparatuses. Specifically, the present invention is suitably applicable to a projection exposure apparatus, e.g., of a step-and-repeat or a step-and-scan type, as a kind of fabrication apparatus used in a lithography process for devices such as semiconductor devices, which properly illuminates reticle and wafer surfaces to facilitate a high resolution.
The conventional process for fabricating semiconductor chips sequentially overlays and transfers minute patterns created on multiple masks onto a wafer surface.
This operation uses an illumination apparatus in an exposure apparatus to illuminate a mask (or reticle) arranged in a position optically conjugate with the wafer, so as to project and transfer a pattern on the mask onto the wafer surface via a projection lens.
The image quality of the pattern transferred onto the wafer is primarily dependent on the performance of the illumination apparatus, for example, the uniformity of its luminous intensity distribution on the mask and wafer. For example, Japanese Laid-Open Patent Application No. 10-270312 discloses the illumination apparatus that uses an inner-surface reflecting optical integrator (or a beam mixer) and a wave-front splitting optical integrator (or a multi-beam generating means) to improve the uniformity of the luminous intensity distribution.
FIG. 5
shows a partial schematic view of a projection exposure apparatus that uses an illumination apparatus which employs inner-surface reflecting and a wave-front splitting integrators.
FIG. 5
shows a step-and-repeat or step-and-scan projection exposure apparatus used for fabricating semiconductor chips such as LSIs and VLSIs, and devices such as CCDs, magnetic sensors, and liquid crystal devices.
In
FIG. 5
,
1
denotes a laser light source such as an ArF or KrF excimer laser.
2
denotes an incoherently turning optical system (a coherency decreasing means) that turns a coherent laser beam from the light source
1
into an incoherent one so that there may be no speckles on a plate
12
.
3
denotes a beam shaping optical system for shaping a beam from the incoherently turning optical system
2
into a desired beam shape.
4
denotes an optical element for retaining an angle of exit, and for serving to maintain the angle of exit constant regardless of a status of an incident beam.
5
is a condensing optical system, which condenses beams from the optical element
4
and leads them to a plane of incidence
6
a
of the optical pipe
6
(or beam mixing means). The beam mixing means
6
uses beams from the condensing optical system
5
to create multiple virtual light sources (virtual images of the light source), and mix beams from multiple virtual light sources so as to make the luminous intensity distribution uniform on the plane of exit
6
a.
7
denotes a zoom optical system (or image-forming system). This optical system
7
projects beams from the beam mixing means
6
onto a plane of incidence
8
a
of a fly-eye lens as the multiple beams generating means
8
under various magnifications, and enables (a coherence factor) o to change continuously during zooming. At that time, the optical pipe
6
's plane of exit
6
b
and the fly-eye lens
8
's plane of incidence
8
a
are approximately conjugate with each other. In other words, the optical system
8
can form an image on the plane of exit
6
b
onto the plane of incidence
8
a
, and change the image size.
The fly-eye lens
8
forms multiple secondary light source images in the neighborhood of its plane of exit
8
b.
9
denotes an irradiating means including a condenser lens and the like, which condenses a beam from each element lens in the multiple beams generating means
8
, and superimposes and uniformly illuminates a plane to be irradiated
10
as a plane forming a pattern on a mask or reticle (called a “reticle” hereinafter).
11
is a projection optical system. The optical system
11
has a telecentric system at the side of its plane of exit, and demagnifies and projects the pattern on the reticle
10
onto the wafer (plate)
12
.
FIG.
6
(A) is a schematic view from the optical pipe
6
to the wafer
12
in the above conventional example described above, addressing o (or the size of an illumination beam within a plane of pupil) in the projection optical system
11
, where the optical pipe
6
has a square cross section.
Optical pipe
6
's plane of exit
6
b
that includes the square cross section is transcribed to the fly-eye lens
8
's plane of incidence
8
a
in an approximately conjugate manner through a zoom optical system
7
. Since the fly-eye lens
8
is an aggregate of element lenses, the light quantity distribution on the plane of incidence
8
a
is transmitted on an as-is basis to the plane of exit
8
b.
Therefore, for the square
6
b
in this case,
8
b
also has a square light quantity distribution.
Beams exiting from the fly-eye lens
8
's plane of exit
8
b
pass through the condenser lens
9
and Kohler-illuminates the reticle
10
. The plane of exit
8
b
and projection optical system
11
's plane of pupil
11
pupil
are in an approximately conjugate relationship.
If a distribution of illumination light in projection optical system
11
's plane of pupil
11
pupil
is indicated as
11
illum
, the illumination light distribution
11
illum
also becomes a square distribution from the above relationship as shown in FIG.
6
(B). &sgr; represents the magnitude of the illumination light in projection optical system's plane of pupil. However, in this case, a ratio between &sgr;0 in a direction of 0° (or a vertical direction in the figure) and &sgr;45 in a direction of 45° to the direction 0° is a ratio between a side length and a diagonal length in a square, as can be understood from FIG.
6
(B). Consequently, &sgr;45 is 1.41 times as large as &sgr;0.
This means that open angles (NA) of a beam that illuminates one spot on the reticle
10
differs in the directions of 0° and 45°, which, in turn, means that a difference in resolving power occurs in relation to these two directions when a pattern on the reticle
10
is projected onto the wafer
12
.
A &sgr; adjustment stop having, e.g., a circular aperture, when provided before the fly-eye lens
8
′ plane of exit
8
b
would eliminate the foregoing anisotropy of &sgr;. However, this requires so many &sgr; adjustment stops corresponding to the number of kinds of &sgr; settings, making the continuous &sgr; changing practically impossible.
Accordingly, it is an object of the present invention to provide an improved projection exposure apparatus having no the above &sgr; anisotropy.
In addition, it is a supplementary object to provide a projection exposure apparatus that miniaturizes an illumination system and improves the durability, without lowering luminous intensity, and without necessarily requiring a switching mechanism for the &sgr; adjustment stop at the side of fly-eye lens's plane of exit.
BRIEF SUMMARY OF THE INVENTION
In order to achieve the foregoing object, an illumination apparatus of one aspect of the present invention includes an inner-surface reflecting type integrator, an optical system for directing a beam from a light source to a portion of incidence of the inner-surface reflecting type integrator, an wave-front splitting type integrator, an image-forming optical system for arranging the portion of incidence of the inner-surface reflecting type integrator approximately conjugate with a portion of incidence of the wave-front splitting type integrator, and for directing a beam from the beam mixer to the wave-front splitting type integrator, and an irradiating optical system for superimposing multiple beams from the wave-front splitting type integrator on a plane to be irradiated, wherein a stop is provided at or near the portion of exit of the inner-surface reflecting type integrator.
The inner-surface reflecting type integrator may reflect at least a part of incident
Canon Kabushiki Kaisha
Epps Georgia
Harrington Alicia M.
Morgan & Finnegan , LLP
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