Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1997-02-11
2001-07-10
Mahoney, Christopher (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
Reexamination Certificate
active
06259513
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to semiconductor manufacturing, and more particularly to an illumination system that is spatially controllable and matched to a reticle.
BACKGROUND OF THE INVENTION
Photolithography is often used in the manufacture of semiconductors. A reticle having a circuit pattern thereon is projected onto a photosensitive substrate such as a wafer. The wafer is subsequently processed, forming patterns thereon. This process is generally repeated several times, forming multiple layers. As the art develops and the element sizes of the semiconductor devices become smaller, there is a need for improved illumination sources for projecting the image of a reticle onto a photosensitive substrate. Accordingly, there have been many illumination systems disclosed in an effort to enhance the imaging of a reticle onto a photosensitive substrate. One such illumination system is disclosed in U.S. Pat. No. 5,296,892 entitled “Illuminating Apparatus and Projection Exposure Apparatus Provided With Such Illumination Apparatus” issuing to Mori on Mar. 22, 1994, which is herein incorporated by reference. Therein disclosed is an illumination system having an optical integrator or fly's eye lens positioned next to a condenser. The optical integrator or fly's eye lens is designed to be replaceable so that the numerical aperture on the emission side of the illumination system can be varied. Another illumination system is disclosed in U.S. Pat. No. 5,357,312 entitled “Illuminating System In Exposure Apparatus For Photolithography” issuing to Tounai on Oct. 18, 1994, which is herein incorporated by reference. Therein disclosed is an illumination system that desirably shapes a uniformalized light beam reducing loss of illuminating light by blockage of an aperture diaphragm. Additionally, the cross sectional shape of the light beam can be rendered annular. Yet another illumination system is disclosed in U.S. Pat. No. 5,329,336 entitled “Exposure Method and Apparatus” issuing to Hirano et al. on Jul. 12, 1994. Therein disclosed is an exposure apparatus having a detector that is compensated for due to coherence changes in the exposure apparatus. Additionally, the concept of zone and modified light source illumination is disclosed for the purpose of optimizing the image of a reticle pattern. Accordingly, there is a need to provide different illumination characteristics for different reticle geometries or patterns. However, due to the complexity of illumination sources and the difficulty of modifying them for a specific reticle pattern or geometry, often it is difficult to provide an optimized illumination pattern for a specific reticle. As a result, some portions of a reticle may be illuminated adequately while others are not. This may result in different imaging results on different portions of a wafer. Therefore, there is a need for an illumination system that optimizes the exposure of a photosensitive substrate irrespective of the different reticle patterns or geometries contained thereon.
SUMMARY OF THE INVENTION
The present invention relates to the use of an optical element which may be a microlens array that is divided into a plurality of different illumination regions, providing different illumination characteristics or profiles for each region. The optical element with its plurality of different regions is matched to a reticle having a plurality of different pattern regions containing different geometries or patterns spatially thereon. Each of the plurality of different illumination regions on the optical element is matched to each of the plurality of different pattern regions on the reticle so as to provide an overall optimized illumination pattern, providing for improved imaging of the reticle irrespective of the differing patterns or geometries contained thereon.
It is an object of the present invention to optimize the performance of an illumination system irrespective of reticle patterns or geometries.
It is another object of the present invention that certain imperfections in the optics of a photolithographic tool may be compensated for easily.
It is an advantage of the present invention that the illumination system can easily be changed to match a particular reticle.
It is a feature of the present invention that different illumination regions of an optical element are matched to different pattern regions of a reticle.
These and other objects, advantages, and features will become readily apparent in view of the following detailed description.
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Gallatin Gregg
McCullough Andrew W.
Fattibene Arthur T.
Fattibene Paul A.
Fattibene & Fattibene
Mahoney Christopher
SVG Lithography Systems, Inc.
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