Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2001-06-04
2003-06-24
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S621000, C355S053000, C355S067000, C355S071000
Reexamination Certificate
active
06583937
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an illuminating system having a fly-eye-integrator for a microlithographic projection exposure arrangement. The invention also relates to a microlithographic projection exposure arrangement including an illuminating system having a fly-eye-integrator and a method for producing microstructured components with a microlithographic projection exposure arrangement including an illuminating system having a fly-eye-integrator.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,682,885 discloses an illuminating system of the kind referred to above. The light of a mercury vapor lamp is received by an elliptical collector mirror and is directed onto an optical integrator which is configured as a special embodiment of a fly-eye-integrator. The optical integrator mixes light and generates a plurality of light beams which are superposed in an image plane by a condenser optic and there illuminate a rectangularly-shaped field. The optical integrator comprises two pairs of plates having cylinder lenses. The cylinder axes of the cylinder lenses of a pair are parallel and the cylinder axes of the pairs are directed perpendicularly to each other. The two plates of a pair are mounted in the mutually opposite focal plane of the cylinder lenses. A rectangularly-shaped field having a lateral aspect ratio of greater than 1:1 is illuminated in the image plane via focal lengths of the two pairs with the focal lengths being of different sizes.
U.S. Pat. No. 5,926,257 discloses an illuminating system having a fly-eye-integrator which has a configuration similar to the fly-eye-integrator disclosed in U.S. Pat. No. 4,682,885. The cylindrical lenses are configured as diffractive elements having a cylindrical effect.
U.S. Pat. No. 5,963,305 likewise discloses a fly-eye-integrator comprising two pairs of plates with cylindrical lenses wherein the pairs of plates are arranged perpendicularly to each other. Refractive and diffractive embodiments of the cylinder lenses are shown.
The fly-eye-integrators disclosed in U.S. Pat. Nos. 4,682,885; 5,926,257 and 5,963,305 have the disadvantage that the diaphragm plane of the illuminating system downstream of the fly-eye-integrator is only incompletely illuminated when the beam, which impinges on the fly-eye-integrator, has only a slight divergence. A beam of this kind is generated, for example, by a laser light source and is broken up into a plurality of beams by the crossed cylinder lens plates. These beams are focused in the diaphragm plane of the illuminating system and there form a lattice of secondary light sources. The secondary light sources are only point shaped because of the slight divergence of the beam at the entrance of the fly-eye-integrator. The diaphragm plane is therefore only illuminated with discrete intensity peaks. For the fly-eye-integrators having refractive cylinder lenses, the number of the illuminated cylinder lenses is in the order of magnitude of 10
1
. For this reason, only secondary light sources in the order of magnitude of 10
2
are disposed in the diaphragm plane. With the use of diffractive elements having a cylindrical effect, the number of secondary light sources can be increased because of the lesser element width; however, very high requirements are imposed on the quality of the diffractive element and especially on the peripheral sharpness by the very large imaging scale between the diffractive elements and the field to be illuminated.
The two pairs of cylinder lens plates in U.S. Pat. Nos. 4,682,885; 5,926,257 and 5,963,305 have different focal lengths and the cylinder lens plates of a pair, which are arranged downstream in respective light paths, are mounted in the vicinity of the diaphragm plane. For this reason, the cylinder lens plates of the two pairs, which are mounted upstream each in respective light directions, are arranged axially separated. If the fly-eye-integrator is illuminated with a beam of finite divergence such as generated by a mercury vapor lamp, then the axial separation of the upstream-mounted cylinder lens plates leads to an elliptical illumination of the diaphragm plane. The illumination of the image plane should be as rotationally symmetrical as possible for use in microlithography. For this reason, the use of additional diaphragms or filters is required whereby a light loss occurs.
U.S. Pat. No. 5,847,746 discloses an illuminating system which utilizes two crossed cylinder lens plates of different focal length for mixing light. The cylinder lens plates are illuminated with a parallel light beam of slight divergence. To avoid the situation that the diaphragm plane of a downstream projection objective is illuminated pointwise by intensity peaks, the focal lengths of the two cylinder lens plates are so adjusted that the secondary light sources are split into meridional and sagittal secondary light sources which are arranged so as to be defocused. In this way, the intensity peaks in the diaphragm plane are pulled apart to lines of lesser maximum intensity. Disadvantageous in this arrangement is the only partial illumination of the diaphragm plane and the fact that the point symmetry of the diaphragm illumination, which is usually desired, is deteriorated by the line-shaped intensity peaks.
U.S. Pat. No. 5,815,248 shows the use of a one-dimensional lattice in front of a fly-eye-integrator. The fly-eye-integrator does not comprise individual plates having cylinder lenses but a plate having rod-shaped lens elements which are arranged in a two-dimensional array. The lens elements must have an equally sized lateral aspect ratio for a field having a high lateral aspect ratio which is to be illuminated. Correspondingly, the secondary light sources, which are generated by the lens elements in the diaphragm plane, are non-uniformly distributed without the one-dimensional grid. With the aid of the one-dimensional grid, the array having lens elements is illuminated from three directions lying in a plane so that the number of secondary light sources, which are generated by the array, is increased. In this way, a more uniform distribution of the secondary light sources is obtained in the diaphragm plane which follows the fly-eye-integrator. The disadvantage of the use of a one-dimensional grid is the fact that the illumination of the diaphragm plane comprises discrete intensity peaks and no homogeneous illumination is achieved. In addition, the optical channels, which are generated by the lens elements, have a high lateral aspect ratio so that a large portion of the light channels is only partially illuminated in the conventional circular-shaped illumination of the fly-eye-integrator.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an illuminating system for vacuum ultraviolet microlithography which operates in the vacuum ultraviolet range.
A first embodiment of the invention is an illuminating system for vacuum-ultraviolet (VUV) microlithography with a fly-eye-integrator as an optical integrator. A microlens array having rectangular-shaped individual lenses is mounted ahead of the fly-eye-integrator for increasing divergence. The fly-eye-integrator comprises two fly-eye-plates mounted in mutually opposite focal planes and these fly-eye-plates are formed from an array of individual lenses or from two crossed cylinder lens plates. The optical channels have a similar lateral aspect ratio as the field to be illuminated. The optical channels are formed by the individual lenses or the crossed cylindrical lenses. In order to be able to uniformly illuminate the diaphragm plane, the rectangular-shaped microlenses must have a similar lateral aspect ratio as the optical channels in order to increase divergence.
With this embodiment, it is disadvantageous that, for a field having a high lateral aspect ratio, the individual lenses likewise have to exhibit a high lateral aspect ratio. Such individual lenses are complex to produce. If one utilizes crossed cylindrical lens plates for the fly-eye plates, then the width of the cylinder lenses differs greatly for the two align
Köhler Jess
Wangler Johannes
Carl-Zeiss Stiftung
Dinh Jack
Epps Georgia
Ottesen Walter
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