Illumination optical system and method of making exposure...

Details Illumination optical system and method of making exposure... Illumination optical system and method of making exposure...

2002-09-10

2004-03-23

Spector, David N. (Department: 2873)

Optical: systems and elements

Lens

With field curvature shaping

C356S124000, C356S128000, C359S648000

Reexamination Certificate

active

06710930

ABSTRACT:

BACKGROUD OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical system using one or a plurality of optical members (lens and the like) having an uneven optical characteristics (e.g., uneven radial refractive index about an optical axis); and, in particular, to a projection optical system for projecting and transferring a pattern on a projection original onto a photosensitive substrate, or an illumination optical system for illuminating the projection original. Further, the present invention relates to a method of making a projection optical system, a method of making an illumination optical system, a method of making an exposure apparatus, an exposure method, and a method of making a micro device.
2. Related Background Art
In a step of making a semiconductor circuit device, a liquid crystal display device, or the like, an exposure apparatus is used. This exposure apparatus is an apparatus for projecting and transferring a pattern on a projection original such as reticle or mask onto a photosensitive substrate such as wafer or glass plate byway of a projection optical system. In order to project a fine mask pattern onto the photosensitive substrate, the projection optical system requires a very high optical performance in that it has a high resolution with nearly no aberration.
Hence, in order to correct the aberration resulting from a manufacturing error upon assembling the projection optical system, the thickness or the like of washers in the lens barrel for holding optical members such as lens has been changed, lens surfaces have been reground, and so forth.
For achieving a higher accuracy and larger NA in the projection optical system, the in-homogeneousness in refractive index within the lenses has been becoming a factor which is not negligible. The in-homogeneousness in refractive index within the lenses cannot be neglected in particular when there are a large number of constituent lenses.
This in-homogeneousness in refractive index within lenses cannot be corrected by changing the thickness or the like of washers or repolishing lens surfaces. Therefore, it has conventionally been impossible to make lenses from ingots of lenses which do not fall within a tolerance for use.
However, if ingots whose evenness of refractive index does not fall within the tolerance for use are discarded, then the efficiency of making lenses will decrease, thus lowering the efficiency of making projection optical systems. This problem relates to not only the making of projection optical systems, but also the making of illumination optical systems or the making of various kinds of apparatus such as inspection apparatus requiring high optical performances.
SUMMARY OF INVENTION
It is an object of the present invention to provide methods of making various kinds of optical systems such as projection optical systems which use one or a plurality of optical members (lens and the like) having an uneven refractive index and can secure required optical performances, and methods of making various kinds of apparatus.
In most of lenses having an uneven refractive index, the in-homogeneousness of refractive index is distributed in the radial direction, whereas the refractive index is uniform in the circumferential direction. Taking account of this point, the present invention overcomes the above-mentioned problem. Namely, it provides an optical system using one or a plurality of lenses whose radial refractive index about an optical axis is uneven, and having one or a plurality of aspheric surfaces for correcting an aberration caused by the in-homogeneousness of refractive index in the lenses. Preferably, the optical system is a projection optical system for projecting and transferring a pattern on a projection original onto a photosensitive substrate or an illumination optical system for illuminating the projection original, for example.
Thus, the present invention corrects the aberration deteriorated due to the use of lenses having an uneven refractive index distribution by employing aspheric surfaces.
Preferably, in the present invention, each of the lenses with the uneven refractive index has the following relationship:
[Expression 1]
n
max
−n
min
>1×10
−7
  (1)
where n
max
is the maximum value of refractive index, and n
min
is the minimum value of refractive index. Namely, it is preferred that, if (1) is satisfied, then the lens be considered to have an uneven refractive index, and its resulting aberration be corrected by an aspheric surface.
Conversely, if the degree of in-homogeneousness in refractive index is outside of the range according to expression (1), then the refractive index distribution of the lens can be considered substantially uniform. Hence, if the aberration resulting from such a lens is to be corrected by an aspheric surface, then the difference between the aspheric surface and spherical surface (sag amount) becomes so small that it will be meaningless to introduce the aspheric surface.
Preferably, the projection optical system of the present invention is constituted, successively from the projection original side, by a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a negative refracting power, a fifth lens group having a positive refracting power, and a sixth lens group having a positive refracting power.
The first lens group having a positive refracting power mainly contributes to correction of distortion, while maintaining a telecentric property on the object side. Namely, a positive distortion is generated by the first lens group, so as to keep a balance with the negative distortion generated by the second and fourth lens groups.
The second and fourth lens groups having a negative refracting power mainly contribute to correction of Petzval sum. The second and third lens groups form an inverted Galilean system and not only adjusts magnification but also contributes to securing a back focus in the projection optical system.
The fifth and sixth lens groups having a positive refracting power contributes to restraining distortion from occurring and, in particular, to restraining spherical aberration from occurring.
In the case where the projection optical system has the six-group configuration mentioned above, it preferably satisfies:
[Expression 2]
0.04
<|f
4
/L<
0.2  (2)
0.02
<f
5
/L<
0.9  (3)
0.02
<f
6
/L<
1.5  (4)
D
56
/L<
0.3  (5)
0.5
<D
6
/R
6
<1.5  (6)
Here,
f
i
is the focal length of the i-th lens group (i=4, 5, 6);
L is the distance from the object surface to the image plane on the optical axis;
D
56
is the interval between the fifth and sixth lens groups;
D
6
is the distance from the lens surface closest to the object in the sixth lens group to the image plane on the optical axis; and
R
6
is the radius of curvature of the lens surface closest to the object in the sixth lens group on the optical axis.
Conditional expression (2) relates to the balance between spherical aberration and coma. If the lower limit of conditional expression (2) is not satisfied, then aspherical aberration is harder to correct, and it becomes further difficult to use a lens having an uneven refractive index. If its upper limit is exceeded, by contrast, then coma occurs, and it also becomes difficult to use a lens with an uneven refractive index.
Conditional expression (3) relates to a balance among spherical aberration, distortion, and Petzval sum. If the lower limit of conditional expression (3) is not satisfied, then negative distortion and negative spherical aberration enhance, and it becomes further difficult to use a lens with an uneven refractive index. If its upper limit is exceeded, by contrast, then it becomes harder to correct Petzval sum favorably, and it also becomes difficult to use a lens with an uneven refractive index.
Conditional expression (4) relates to the ba

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