Exposure apparatus

Details Exposure apparatus Exposure apparatus

2001-01-31

2004-03-16

Lester, Evelyn (Department: 2873)

Optical: systems and elements

Lens

With field curvature shaping

C359S656000, C359S658000, C359S679000, C359S757000, C359S773000

Reissue Patent

active

RE038465

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus having a projection optical system for projecting a pattern of a first object onto a photosensitive substrate or the like as a second object, and more particularly to a projection optical system suitably applicable to projection exposure of a pattern for semiconductor or liquid crystal formed on a reticle (mask) as the first object onto the substrate (semiconductor wafer, plate, etc.) as the second object.
2. Related Background Art
As the patterns of integrated circuits become finer and finer, the resolving power required for the exposure apparatus used in printing of wafer also becomes higher and higher. In addition to the improvement in resolving power, the projection optical systems of the exposure apparatus are required to decrease image stress.
Here, the image stress includes those due to bowing or the like of the printed wafer on the image side of projection optical system and those due to bowing or the like of the reticle with circuit pattern written therein, on the object side of projection optical system, as well as distortion caused by the projection optical system.
With a recent further progress of fineness tendency of transfer patterns, demands for decreasing the image stress are also becoming greater.
In order to decrease effects of the wafer bowing on the image stress, the conventional technology has employed the so-called image-side telecentric optical system that locates the exit pupil position at a farther point on the image side of projection optical system.
On the other hand, the image stress due to the bowing of reticle can also be reduced by employing a so-called object-side telecentric optical system that locates the entrance pupil position of projection optical system at a farther point from the object plane, and there are suggestions to locate the entrance pupil position of projection optical system at a relatively far position from the object plane as described. Examples of those suggestions are described for example in Japanese Laid-open Patent Applications No. 63-118115 and No. 5-173065 and U.S. Pat. No. 5,260,832.
SUMMARY OF THE INVENTION
An object of the invention is to provide an exposure apparatus having a high-performance projection optical system which can correct the aberrations, particularly the distortion, very well even in the bitelecentric arrangement while keeping a relatively wide exposure area and a large numerical aperture.
To achieve the above object, the present invention involves an exposure apparatus having a high-performance projection optical system comprising a stage allowing a photosensitive substrate (for example, a semiconductor wafer coated with a photosensitive material such as a photoresist) to be held on a main surface thereof, an illumination optical system having a light source for emitting exposure light of a predetermined wavelength and transferring a predetermined pattern on a mask onto the substrate, and a projecting optical system for projecting an image of the mask, on the substrate surface. The above projecting optical system projects an image of a first object (for example, a mask with a pattern such as an integrated circuit) onto a second object (for example, a photosensitive substrate).
As shown in
FIG. 1
, the projection optical system has a first lens group G
1
with positive refracting power, a second lens group G
2
with negative refracting power, a third lens group G
3
with positive refracting power, a fourth lens group G
4
with negative refracting power, a fifth lens group G
5
with positive refracting power, and a sixth lens group G
6
with positive refracting power in the named order from the side of the first object R. The and the second lens group G
2
further comprises a front lens L
2F
placed as closest to the first object R and having negative refracting power with a concave surface to the second object W, a rear lens L
2R
placed as closest to the second object and having negative refracting power with a concave surface to the first object R, and an intermediate lens group G
2M
placed between the front lens L
2F
in the second lens group G
2
and the rear lens L
2R
in the second lens group G
2
. The intermediate lens group G
2M
has a first lens L
M1
with positive refracting power, a second lens L
M2
with negative refracting power, a third lens L
M3
with negative refracting power, and a fourth lens L
M4
with negative refracting power in the named order from the side of the first object R.
First, the first lens group G
1
with positive refracting power contributes mainly to a correction of distortion while maintaining telecentricity, and specifically, the first lens group G
1
is arranged to generate a positive distortion to correct in a good balance negative distortions caused by the plurality of lens groups located on the second object side after the first lens group G
1
. The second lens group G
2
with negative refracting power and the fourth lens group G
4
with negative refracting power contribute mainly to a correction of Petzval sum to make the image plane flat. The two lens groups of the second lens group G
2
with negative refracting power and the third lens group G
3
with positive refracting power form an inverse telescopic system to contribute to guarantee of back focus (a distance from an optical surface such as a lens surface closest to the second object W in the projection optical system to the second object W) in the projection optical system. The fifth lens group G
5
with positive refracting power and the sixth lens group G
6
similarly with positive refracting power contribute mainly to suppressing generation of distortion and suppressing generation particularly of spherical aberration as much as possible in order to fully support high NA structure on the second object side.
Based on the above structure, the front lens L
2F
placed as closest to the first object R in the second lens group G
2
and having the negative refracting power with a concave surface to the second object W contributes to corrections of curvature of field and coma, and the rear lens L
2R
placed as closest to the second object W in the second lens group G
2
and having the negative refracting power with a concave surface to the first object R to corrections of curvature of field, coma, and astigmatism. In the intermediate lens group G
2M
placed between the front lens L
2F
and the rear lens L
2R
, the first lens L
M1
with positive refracting power contributes to a correction of negative distortions caused by the second to fourth lenses L
M2
-L
M4
with negative refracting power greatly contributing to the correction of curvature of field.
In particular, in the above projecting optical system, the following conditions (1) to (5) are satisfied when a focal length of the first lens group G
1
is f
1
, a focal length of the second lens group G
2
is f
2
,a focal length of the third lens group G
3
is f
3
, a focal length of the fourth lens group G
4
is f
4
, a focal length of the fifth lens group G
2
is f
5
,a focal length of the sixth lens group G
6
is f
6
,an overall focal length of the second to the fourth lenses L
M2
-L
M4
in the intermediate lens group G
2M
in the second lens group G
2
is f
n
, and a distance from the first object R to the second object W is L:
0.1<f
1
/f
3
<17  (1)
0.1<f
2
/f
4
<14  (2)
0.1<f
5
/L<0.9  (3)
0.1<f
6
/L<1.6  (4)
0.1<f
n
/f
2
<2.0  (5)
The condition (1) defines an optimum ratio between the focal length f
1
of the first lens group G
1
with positive refracting power and the focal length f
3
of the third lens group G
3
with positive refracting power, which is an optimum refracting power (power) balance between the first lens group G
1
and the third lens group G
3
. This condition (1) is mainly for correcting the distortion in a good balance. Below the lower limit of this condition (1) a large negative distortion is produced because the refracting power of the third len

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