Optical: systems and elements – Lens – Multiple component lenses
Reissue Patent
2000-11-13
2002-09-17
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S649000, C430S311000
Reissue Patent
active
RE037846
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 etc. 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. In order to get ready for the finer tendency of transfer patterns, light sources for exposure have recently been changing from those emitting the light of exposure wavelength of the g-line (436 nm) to those emitting the light of exposure wavelength of the i-line (365 nm) that are mainly used at present. Further, a trend is to use light sources emitting shorter wavelengths, for example the excimer laser (KrF:248 nm, ArF:193 nm).
Here, the image stress includes those due to bowing etc. of the printed wafer on the image side of projection optical system and those due to bowing etc. of the reticle with circuit pattern etc. 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 to decrease the image stress are also becoming harder.
Then, 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 located 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 present invention is to provide a high-performance projection optical system which can achieve the bitelecentricity in a compact design as securing a wide exposure area and a large numerical aperture and which can be well corrected for aberrations, particularly which can be very well corrected for distortion. The projection optical system can be applied to an exposure apparatus.
To achieve the above object, an exposure apparatus according to the present invention comprises at least a wafer stage allowing a photosensitive substrate to be held on a main surface thereof, an illumination optical system for emitting exposure light of a predetermined wavelength and transferring a predetermined pattern of a mask (reticle) onto the substrate, a projection optical system provided between a first surface on which the mask as a first object is disposed and a second surface on which a surface of the substrate as a second object is corresponded, for projecting an image of the pattern of the mask onto the substrate. The illumination optical system includes as alignment optical system for adjusting a relative positions between the mask and the wafer, and the mask is disposed on a reticle stage which is movable in parallel with respect to the main surface of the wafer stage. The projection optical system has a space permitting an aperture stop to be set therein. The photosensitive substrate comprises a wafer such as a silicon wafer or a glass plate, etc., and a photosensitive material such as a photoresist or the like coating a surface of the wafer. In particular, as shown in
FIG. 1
, the projection optical system includes a first lens group (G
1
) with a positive refracting power, a second lens group (G
2
) with a negative refracting power, a third lens group (G
3
) with a positive refracting power, a fourth lens group (G
4
) with a negative refracting power, a fifth lens group (G
5
) with a positive refracting power, and a sixth lens group (G
6
) with a positive refracting power in order from the side of the first object (for example, a mask).
The second lens group (G
2
) comprises a front lens (L
2F
) with a negative refracting power disposed as closest to the first object and shaded with a concave surface to the second object, a rear lens (L
2R
) of a negative meniscus shape disposed as closest to the substrate and shaped with a concave surface to the mask, and an intermediate lens group (G
2M
) disposed between the front lens (L
2F
) and the rear lens (L
2R
). In particular, the intermediate lens group (G
2M
) has a first lens (L
M1
) with a positive refracting power, a second lens (L
M2
) with a negative refracting power, and a third lens (L
M3
) with a negative refracting power in order from the side of the first object.
Further, the projection optical system according to the present invention is arranged to satisfy the following conditions (1) to (6) when f
1
is a focal length of the first lens group (G
1
), f
2
is a focal length of the second lens group (G
2
), f
3
is a focal length of the third lens group (G
3
), f
4
is a focal length of the fourth lens group (G
4
), f
5
is a focal length of the fifth lens group (G
5
), f
6
is a focal length of the sixth lens group (G
6
), and L is a distance from the first object to the second object:
(1) f
1
/L<0.8
(2) −0.033<f
2
/L
(3) 0.01<f
3
/L<1.0
(4) f
4
/L<−0.005
(5) 0.01<f
5
/L<0.9
(6) 0.02<f
6
/L<1.6.
The projection optical system is so arranged as to have at least the first lens group (G
1
) with positive refracting power, the second lens group (G
2
) with negative refracting power, the third lens group (G
3
) with positive refracting power, the fourth lens group (G
4
) with negative refracting power, the fifth lens group (G
5
) with positive refracting power, and the sixth lens group (G
6
) with positive refracting power in the named order from the first object side.
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 in the projection optical system to the second object) 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 arrangement, the front lens (L
2F
) with the negative refracting power disposed as closest to the first object in the second lens group (G
2
) and shaped with the concave surface to the second o
Endo Kazumasa
Kobayashi Misako
Matsuzawa Hitoshi
Suenaga Yutaka
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