Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2002-09-24
2004-01-06
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C359S618000
Reexamination Certificate
active
06674513
ABSTRACT:
TECHNICAL FIELD
The present invention relates to projection exposure apparatus and methods used in fabrication of microdevices, for example, such as semiconductor integrated circuits, imaging devices including CCDs and the like, liquid crystal displays, or thin-film magnetic heads by the lithography technology, and to projection optical systems suitably applicable to such projection exposure apparatus. The present invention also relates to methods of fabricating the foregoing projection exposure apparatus and projection optical systems.
BACKGROUND ART
As the circuit patterns for such microdevices as the semiconductor integrated circuits and others are becoming finer and finer in recent years, the wavelengths of illumination light(radiation) for exposure (exposure light(radiation)) used in the exposure apparatus such as steppers and the like have been decreasing toward shorter wavelengths year after year. Namely, as the exposure light, KrF excimer laser light (wavelength: 248 nm) is going mainstream in place of the i-line (wavelength: 365 nm) of mercury lamps mainly used conventionally, and ArF excimer laser light of a much shorter wavelength (wavelength: 193 nm) is also nearing practical use. For the purpose of further decreasing the wavelength of the exposure light, there are also attempts to use halogen molecular lasers and others like the F
2
laser (wavelength: 157 nm).
Although the aforementioned excimer lasers, halogen molecular lasers, etc. are available as light sources in the vacuum ultraviolet region of wavelengths not more than 200 nm, there are limits to practical band narrowing thereof.
Since limited materials transmit the emitted light in this vacuum ultraviolet region, available materials are limited for lens elements constituting the projection optical systems and transmittances of the limited materials are not so high, either. As matters now stand, the performance of antireflection coats provided on surfaces of the lens elements is not so high, as against those for longer wavelengths.
A first object of the present invention is to suppress chromatic aberration of the projection optical system and reduce loads on the light source.
A second object of the present invention is to correct chromatic aberration for the exposure light having some spectral width, by adding a single kind of glass material or a few color-correcting glass materials.
A third object of the present invention is to obtain an extremely fine microdevice circuit pattern while simplifying the structure of the projection optical system.
A fourth object of the present invention is to obtain an extremely fine microdevice circuit pattern without decrease in throughput.
DISCLOSURE OF THE INVENTION
For accomplishing the foregoing first or second object, a first projection optical system according to the present invention is a dioptric projection optical system for forming an image of a pattern on a first surface, onto a second surface by action of light-transmitting (radiation-transmitting) refractors, comprising: a front lens unit having a positive refracting power, located in an optical path between the first surface and the second surface; a rear lens unit having a positive refracting power, located in an optical path between the front lens unit and the second surface; and an aperture stop located in the vicinity of a rear focus position of the front lens unit; the projection optical system being telecentric on the first surface side and on the second surface side, wherein the following condition is satisfied:
0.065
<f
2/
L<
0.125,
where f2 is a focal length of the rear lens unit and L is a distance from the first surface to the second surface.
A first fabrication method of a projection optical system according to the present invention is a method of fabricating a dioptric projection optical system for forming an image of a pattern on a first surface, onto a second surface by action of radiation-transmitting refractors, comprising: a step of locating a front lens unit having a positive refracting power; a step of locating a rear lens unit having a positive refracting power, between the front lens unit and the second surface; and a step of locating an aperture stop between the front lens unit and the rear lens unit; wherein the front lens unit, the rear lens unit, and the aperture stop are located so that the projection optical system is telecentric on the first surface side and on the second surface side, and said method using the projection optical system satisfying the following condition;
0.065
<f
2/
L<
0.125,
where f2 is a focal length of the rear lens unit and L a distance from the first surface to the second surface.
For accomplishing the foregoing first or second object, a second projection optical system according to the present invention is a dioptric projection optical system for forming an image of a pattern on a first surface, onto a second surface by action of radiation-transmitting refractors, comprising three or more lenses having their respective refracting powers, wherein when three lenses are selected in order from the first surface side of the lenses having their respective refracting powers, at least one surface of the three lenses is of an aspheric shape having a negative refracting power.
For accomplishing the foregoing first or second object, a third projection optical system according to the present invention is a dioptric projection optical system for forming an image of a pattern on a first surface, onto a second surface by action of radiation-transmitting refractors, comprising a plurality of lenses having their respective refracting powers, wherein when two lenses are selected in order from the first surface of the lenses having their respective refracting powers, at least one surface of the two lenses is an aspheric surface, and wherein, where Ca is a local, principal curvature near a center of an optical axis of the aspheric surface and Cb is a local, principal curvature in the meridional direction of an extreme marginal region of a lens clear aperture diameter of the aspheric surface, the following condition holds if the aspheric surface has a negative refracting power:
Cb/Ca<
0.7 (b-1);
on the other hand, in the present invention, the following condition holds if the aspheric surface has a positive refracting power:
Cb/Ca>
1.6 (b-2).
In this invention, the local, principal curvature Ca near the center of the optical axis of the aspheric surface and the local, principal curvature Cb is in the meridional direction of the extreme marginal region of the lens clear aperture diameter of the aspheric surface can be expressed as follows as an example. That is to say, the aspheric surface is expressed by the following equation (b-3):
Z
(
Y
)
=
Y
2
/
r
1
+
1
-
(
1
+
κ
)
Y
2
/
r
2
+
AY
4
+
BY
6
+
CY
8
+
DY
10
+
EY
12
+
FY
14
,
(b-3)
where Y is a height of the aspheric surface from the optical axis, z a distance along the direction of the optical axis from a tangent plane at the vertex of the aspheric surface to the aspheric surface, r a radius of curvature at the vertex, &kgr; a conical coefficient, and A, B, C, D, E, and F aspheric coefficients.
With this expression, the local, principal curvatures Ca and Cb are given as follows.
Ca=
1/
r
(b-4)
Cb
=
d
2
z
/
d
2
Y
{
1
+
(
dz
/
dY
)
2
}
3
/
2
(b-5)
With increase in the numerical apertures of the projection optical systems and with increase in the size of the image field, there are increasing demands for minimization of distortion. In order to correct only distortion while suppressing influence on the other aberrations, it is preferable to place an aspheric surface for correction of distortion at a position as close to the object plane (mask) as possible. On this occasion, when the aspheric surface satisfies the foregoing condition (b-1) or (b-2), the distortion can be corrected well even with increase in the numerical aperture and with increase in the size of the image field.
For accomplishing the foregoing first or secon
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
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