Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-05-20
2001-09-04
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S071000
Reexamination Certificate
active
06285443
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an illuminating arrangement for a projection microlithographic apparatus having a laser and an objective.
BACKGROUND OF THE INVENTION
Such an arrangement is shown, for example, in U.S. Pat. No. 5,675,401.
Lasers are primarily used as light sources for microlithography because they emit a very narrow band of light and, in the case of excimer lasers, light of very low wavelength in the deep ultraviolet range is emitted. The time-dependent and spatial coherence of these lasers as well as the small cross section and low divergence of the light beam are, however, not adapted to the situation for illuminating devices for microlithography.
Cross section and divergence cannot be changed independently by singular imaging optical elements in the cross section of the light beam as the light-conductance value cannot be increased. The light-conductance value is defined as the luminous flux divided by the luminance. In this context, reference can be made to the text of M. Young entitled “Optics and Lasers”, Springer Verlag (1984), page 51 and the text of K. Mütze et al entitled “ABC der Optik” Verlag Dausien (1961), starting at page 477. The Lagrange invariant is closely related to the maintenance of the light-conductance value. In this connection, reference may be made to the text of M. Young cited above at pages 50 and 51.
Scattering elements are known to increase the light-conductance value. Frosted glass plates or quartz glass plates having statistically orientated microfaces, which act to refract, reflect or diffract, are used for this purpose. The scatter profile of such scattering plates is very intense in the center but also still distributes considerable energy at large angles in a tail portion of a distribution curve of the energy.
A targeted distribution of rays having divergence magnification and cross section magnification is obtainable with lens rasters which are available for the ultraviolet range and the DUV range (deep ultraviolet range).
Diffractive optical raster elements in quartz can be produced by photolithography in the most different embodiments and can be substituted for the raster lens plates.
U.S. Pat. No. 4,936,665 discloses a wafer illuminating system having a wafer stepper, projection objective, excimer laser, radiation forming optics and expansion optics and an illuminating system having several lens groups which, in turn, has an entry pupil. Two divergence generating elements are provided in the entry pupil and in a further plane. In contrast to the present invention, the second plane is likewise a pupillary plane and the two elements are stochastic scattering plates having scattering silicon crystallites. An oscillating mirror is additionally provided.
The foregoing functions to reduce the spatial coherence. The significance of the adaptation of the spatial coherence by magnification of the effective light source for wafer illuminating systems is described.
The two scattering plates cannot possess an anamorphotic effect. Zoom lens, axicon lens and glass rod are not described. A nonrastered diffractive optical element in the form of a blazed transmission grating having concentric multiplateau rings is provided in the pupil of the projection objective to correct aberrations of the wavefront.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an illuminating arrangement of the kind described above which operates at high efficiency and has moderate complexity and which provides an illumination of the wafer with a suitable form of the light spot, divergence, coherence and homogeneity. It is another object of the invention to provide such an illuminating arrangement which is suitable for a wafer stepper as well as for a wafer scanner.
The illuminating arrangement of the invention is for a projection microlithographic apparatus and the arrangement includes: a laser for emitting a light beam along an optical axis; an objective mounted on the axis and having an object plane and an exit pupil plane; a first optical raster element mounted in a plane equivalent to said object plane; a second optical raster element mounted in a plane equivalent to said exit pupil plane; and, each of the optical raster elements having a two-dimensional raster structure.
Two planes are equivalent if they are related by one or more optical imagings within the arrangement, or if they are identical.
For an illuminating arrangement for a projection microlithographic apparatus having a laser and an objective, an optical raster element having a two-dimensional raster structure is arranged in the object plane and in the exit pupil of the objective or in planes equivalent thereto.
With these two raster elements arranged in this manner, the required divergence magnification of the laser light can be used in a targeted manner to form the light beam and to make possible the best degree of efficiency and a simplified configuration of further optical component groups.
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patent: 5636003 (1997-06-01), Tanitsu et al.
patent: 5646715 (1997-07-01), Wangler
patent: 5675401 (1997-10-01), Wangler et al.
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Ittner Gerhard
Wangler Johannes
Adams Russell
Carl-Zeiss-Stiftung
Nguyen Hung Henry
Ottesen Walter
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