Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1998-08-03
2001-07-10
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S071000
Reexamination Certificate
active
06259512
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an illumination system, a projection exposure apparatus having the same, and a device manufacturing method using the same. More particularly, the invention is suitably usable in the manufacture of devices such as semiconductor devices, and applicable to a step-and-repeat type or step-and-scan type projection exposure apparatus, for example, to assure suitable illumination of a pattern on a reticle surface and thus high resolving power
For illumination systems to be used in an exposure apparatus for the manufacture of devices such as semiconductor devices, generally removal of non-uniformness of illuminance upon the surface of a mask (reticle) is strongly required to attain a high resolving power. Japanese Laid-Open Patent Application, Laid-Open No. 913/1989 shows an illumination system which, to meet the above requirement, proposes an attempt to increase the light collection efficiency.
FIG. 34
is a schematic view of a main portion of an illumination system proposed in this document. Denoted in the drawing at
1
is a light source which comprises an ultra-high pressure Hg lamp, for example. Denoted at
2
is light collecting means which comprises an elliptical mirror, for example. The light source
1
is disposed adjacent to a first focal point of the elliptical mirror
2
. Denoted at
3
is light mixing means which comprises an optical pipe of a predetermined shape, having a light entrance surface
3
a
disposed adjacent to a second focal point of the elliptical mirror
2
. Denoted at
4
is a condensing lens, and denoted at
5
is multi-light beam producing means which comprises a fly's eye lens. The condensing lens
4
is so set that the light exit end
3
b
of the optical pipe
3
and the light entrance surface
5
a
of the fly's eye lens
5
are placed substantially in an optically conjugate relation with each other. Also, optical constants of the condensing lens
4
are determined so that the light exit end
3
b
is imaged on the light entrance surface
5
a
at a predetermined magnification.
Denoted at
6
is illuminating means which includes a condenser lens and which serves to illuminate a surface
7
to be illuminated (such as the surface of a mask or reticle) with light from the light exit surface
5
b
of the fly's eye lens
5
.
The light convergence point (rear focal point) of the element lenses, constituting the fly's eye lens
5
, is approximately registered with the front focal point of the light collecting means
6
. Also, the surface
7
to be illuminated and the rear focal point of the light collecting means
6
are approximately registered with each other. Thus, a Koehler illumination system is provided.
The optical pipe
3
which is light mixing means serves to define a number of virtual or real light convergent points from a single light flux, on the basis of multiple reflection by an inside surface thereof. The principle is illustrated in
FIGS. 35-37
.
For example, the optical pipe may be made of a hollow member having a square sectional shape, as shown in
FIG. 37
, for providing inside reflection.
FIG. 35
shows formation, upon a sectional plane along an optical axis, of virtual light convergence points by converged light having a light source image S
0
in front of the light entrance surface
301
a
of the optical pipe
3
. Among the light rays coming from the light source image S
0
, those which are never reflected by any of an upper side face
301
c
and lower side face
301
d
, go directly out of the light exit surface
301
b
. The light reflected once only by the upper side face
301
c
goes out as if it is supplied from a virtual light convergent point S
1
which is optically conjugate with the convergence point S
0
with respect to the upper side face
301
c
. Also, the light reflected once only by the lower side face
301
d
goes out as if it is supplied from a virtual light convergence point S-
1
which is optically conjugate with the convergence point S
0
with respect to the lower side face
301
d.
Similarly, the light reflected by the lower side face
301
d
and then by the upper side face
301
c
goes out as if it is supplied from the light convergence point S
2
. The light reflected by the upper side face
301
c
and then by the lower side face
301
d
goes out as if it is supplied from the convergence point S-
2
.
Thus, the light entering the optical pipe and having the light source image S
0
goes out from the pipe, through single or plural reflections at side faces, as if it is supplied from substantially a number of light sources. As a result of this, the points of light convergence as seen from the light exit surface are such as shown in
FIG. 36
wherein the light exit surface
301
b
is illuminated with lights from a number of light convergence points distributed in a matrix. Thus, a substantial surface light. source is defined on the surface S where these-virtual light convergence points are formed. Consequently, a substantially uniform illuminance distribution can be produced on the light exit end
301
b
of the optical pipe
3
. The degree of uniformness is determined by the number of reflections of light inside the optical pipe, although a detailed description thereof is omitted here.
The fly's eye lens
5
comprises a plurality of arrayed small lenses, and a secondary light source plane is defined at its light exit surface
5
b
. As described above, the light exit surface
301
b
of the optical pipe
3
and the light entrance surface
5
a
of the fly's eye lens
5
are disposed substantially in a conjugate relation with each other. While a substantially uniform illuminance distribution is produced at the light exit surface
3
b
of the optical pipe
3
, it is directed to the fly's eye lens
5
and, through the illuminating means
6
, it is projected to the surface
7
in Koehler illumination, whereby a more uniform illuminance distribution is produced on the surface
7
.
The required resolution of projection exposure apparatuses is increasing with a recent enlargement of the density of a semiconductor device. For improvement of resolution, many attempts have been made such as shortening of a wavelength of a light source, use of, a phase shift mask, or use of a modified illumination method. Particularly, the modified illumination method has an advantage that it does not need a large change to conventional systems and additionally it can be applied directly to conventional mask patterns.
As representative examples of the modified illumination method, generally there are two methods; a method called a quadruple-pole illumination method wherein, upon a predetermined plane in an illumination optical system which is substantially optically conjugate with a pupil of a projection optical system, the passage of light is limited to four locations spaced from the optical axis; and a method called a ring-like zone illumination method wherein, upon a predetermined plane of an illumination system, like the above-described plane, the passage of light is limited to ring-like zones concentric with the optical axis.
The quadruple-pole illumination method has a significant effect of improvement of resolution and enlargement of depth of focus, particularly for a pattern which comprises lateral and longitudinal lines. However, for a pattern having obliquely extending lines, the result will be inferior even to that of an ordinary illumination method without such a modified illumination.
As for a ring-like zone illumination method, on the other hand, while the effect of improvement of resolution and enlargement of depth of focus is not so significant as compared with the quadruple illumination method, it has an advantage of being free from the direction of a pattern.
Japanese Laid-Open Patent Application, Laid-Open No. 251308/1993 shows an illumination system based on a modified illumination method, wherein ring-like light converting means for transforming parallel light into ring-like light is provided between light source means and an integrator,
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mathews Alan A.
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