Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1998-10-14
2001-09-04
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S071000, C362S268000
Reexamination Certificate
active
06285440
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an illumination system and a projection exposure apparatus using the same. More particularly, the invention is concerned with an illumination system and a projection exposure apparatus suitable for use in the manufacture of micro-structure devices such as an IC, LSI, a magnetic head, a liquid crystal panel, or a CCD, for example. Specifically, the invention is directed to a projection exposure apparatus of a step-and-repeat type or step-and-scan type for device manufacture, wherein a pattern of a reticle can be efficiently illuminated and high resolution can be provided easily.
Many proposals have been made upon a reduction type projection exposure apparatus (stepper), in micro-fabrication of semiconductor devices such as an IC or LSI, with which apparatus an image of a circuit pattern of a mask (reticle) is formed on a photosensitive substrate (wafer) through a projection optical system and this is repeated so that the photosensitive substrate is exposed in a step-and-repeat method.
In such steppers, the pattern transfer is performed by projecting a circuit pattern of a reticle to a predetermined position on a wafer surface in a reduced scale, with a projection optical system having a predetermined reduction magnification. After completion of a single pattern projection and transfer, a stage on which the wafer is placed is moved stepwise by a predetermined amount, and the pattern transfer is repeated. This procedure is repeated until exposure of the whole wafer surface is completed.
On the other hand, step-and-scan (scan type) projection exposure apparatuses have recently been proposed, in which a scanning mechanism is used to assure higher resolution and enlargement of picture field size. In such a step-and-scan type projection exposure apparatus, a slit-like illumination region is defined and, for exposure, a reticle and a wafer are scanned by relatively scanning the reticle and the wafer relative to the slit-like illumination region, whereby exposure of one shot is performed. After completion of scan exposure of one shot, the wafer is moved stepwise to the exposure position for the subsequent shot. Then, exposure of this shot is performed. This is repeated until exposure of the whole wafer surface is completed.
In scan type projection exposure apparatuses, the exposure operation is performed while scanning a reticle and a wafer in synchronism with each other. The illumination region upon the reticle surface has a rectangular shape being short in the scan direction and being long in the non-scan direction. For a method of efficiently illuminating such an oblong shape, Japanese Laid-Open Patent Application, Laid-Open No. 203807/1996 proposes a system having a fly's eye lens as an optical integrator for collecting light from a light source and for defining secondary light sources, wherein the section thereof has a shape analogous to the shape of the illumination region. On the other hand, Japanese Laid-Open Patent Application, Laid-Open No. 78002/1992 proposes a structure wherein an optical integrator is provided by combinations of cylindrical lenses disposed on an optical axis.
FIGS. 13A and 13B
are schematic views for illustrating a main portion of an illumination system as proposed in Japanese Published Patent Application, Publication No. 78002/1992. In
FIG. 13A
, light from a light source
21
is reflectively collected by an elliptical mirror
22
toward an optical integrator
6
which comprises four lens assemblies
6
a
-
6
c
. With lights from secondary light sources as defined by this optical integrator, the surface R to be illuminated is illuminated through a condenser lens
8
. As shown in
FIG. 13B
, there are secondary light source images of elliptical shape defined upon the light exit surface of the optical integrator
6
.
However, when a fly's eye lens is used as an optical integrator and when the sectional shape of the lenses of the fly's eye lens is rectangular, there occurs a difference of pitch in disposition of secondary light sources with respect to X and Y directions. This results in a difference in resolution performance between a pattern in the X direction and a pattern in the Y direction.
Further, when a fly's eye lens having combinations of cylindrical lenses disposed along the optical axis direction is used, as illustrated in
FIG. 13B
, if the incidence angle of the light from the light source incident on the fly's eye lens is isometric, the shape of the secondary light source within a single lens element
60
as defined by intersection of the cylindrical lenses as viewed in the Z direction is deformed due to a difference in refractive power depending on the direction, even when the disposition of the cylindrical lens assemblies is even with respect to the X and Y directions. This results in a difference with direction, in the shape of the whole secondary light sources with respect to the X and Y directions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an illumination system and/or a projection exposure apparatus by which no difference is created in shape or disposition of secondary light sources with respect to the X and Y directions.
In accordance with an aspect of the present invention, there is provided an illumination system for illuminating an illumination region having a difference in size along a first direction and a second direction perpendicular to the first direction, said illumination system comprising: an optical integrator for receiving light from a light source, said optical integrator including elements having different refractive powers being different with respect to the first and second directions as said optical integrator is viewed in an optical axis direction, said elements also having the same pitch with respect to the first and second directions, wherein said illumination system satisfies a relation
0.8<[(tan &thgr;
1
/tan &thgr;
2
)/(ø
1
/ø
2
)]<2.1
where &thgr;
1
and &thgr;
2
are largest incidence angles of the light incident on said optical integrator with respect to the first and second directions, and ø
1
and ø
2
are refractive powers of said optical integrator with respect to the first and second directions.
In accordance with another aspect of the present invention, there is provided an illumination system for illuminating an illumination region having a difference in size along a first direction and a second direction perpendicular to the first direction, said illumination system comprising: an optical integrator for receiving light from a light source, said optical integrator including elements having different refractive powers being different with respect to the first and second directions as said optical integrator is viewed in an optical axis direction, said elements also having the same pitch with respect to the first and second directions, wherein said illumination system satisfies a relation
0.8<[(
NA
1
/NA
2
)/(ø
1
/ø
2
)]<2.1
where NA
1
and NA
2
are numerical apertures of the light incident on said optical integrator with respect to the first and second directions, and ø
1
and ø
2
are refractive powers of said optical integrator with respect to the first and second directions.
In accordance with a further aspect of the present invention, there is provided an illumination system for illuminating an illumination region having a difference in size along a first direction and a second direction perpendicular to the first direction, said illumination system comprising: an optical integrator for receiving light from a light source, said optical integrator having (i) a first lens assembly including cylindrical lenses arrayed at a predetermined pitch along the first direction, said cylindrical lenses of said first lens assembly having a refractive power only with respect the first direction, and (ii) a second lens assembly including cylindrical lenses arrayed at a predetermined pitch along the second direction, said cylindrical lenses of said second lens
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Rodney
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