Optical: systems and elements – Glare or unwanted light reduction
Reexamination Certificate
1999-04-19
2001-04-10
Sikder, Mohammad Y. (Department: 2872)
Optical: systems and elements
Glare or unwanted light reduction
C359S608000, C359S227000, C359S231000, C355S053000, C355S071000, C355S067000
Reexamination Certificate
active
06213607
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an exposure apparatus employed for manufacturing a semiconductor device and a liquid crystal display substrate or the like and, more particularly, to an exposure apparatus for performing, a so-called picture synthesization in which a pattern having a large area is formed by overlapping some portions of unit-area patterns with each other on a photosensitive substrate.
2. Related Background Art
This type of exposure apparatus has hitherto involved the use of a picture synthesizing method of eventually synthesizing a desired pattern by partitioning an exposure area into a plurality of unit areas on a photosensitive substrate and repeating an exposure in accordance with each unit area in order to cope with a scale-up (increase in area size of the exposure area) of the photosensitive substrate as an object for exposure. When effecting this picture synthesization, a positional deviation of the pattern is caused by a pattern depicting error of a reticle for a pattern projection, an aberration in a projection optical system and a positioning error of a stage for positioning the photosensitive substrate. For this reason, it follows that pattern breaks appear in positions of boundaries between the respective exposure areas, which should be connected without any gap. For preventing this, very slight quantities of boundaries between the respective exposure areas are overlapped with each other. When the exposure areas are overlapped, however, an exposure quantity of this portion is doubled, resulting in variation in terms of line width of the pattern at the connected portion between the respective exposure areas depending on a characteristic of a photosensitive agent. Further, when the picture synthesization takes place, a stepped portion is produced at the pattern joint lines due to a positional deviation (deviation in the direction orthogonal to the direction in which the pattern extends) between the exposure areas adjacent to each other. It may happen that the characteristic of the device is spoiled. Further, if a different exposure apparatus is burdened per layer (per process) with a process of overlapping the picture-synthesized single-layered patterns with each other in multi layers, an overlap error of the exposure area of each layer discontinuously changes at the pattern joint lines, depending on the aberration of the lens and a difference in terms of a positioning accuracy of each exposure apparatus. As a result, especially in an active matrix liquid crystal device, contrast discontinuously varies at the pattern joint lines, resulting in a decline of a device quality.
A method of obviating the problems inherent in the picture synthesization described above entails a technique disclosed in Japanese Patent Publication No. 63-49218. According to this technique, light reducing or light attenuating portions for reducing a quantity of the transmitted light are provided in positions, corresponding to the pattern joint lines, of a reticle or a filter superposed on the reticle. Then, pattern images passing through the light reducing portions are overlapped with each other on the photosensitive substrate, and, thus, the exposure is effected so that an exposure quantity of the pattern overlapped portion is substantially coincident with the exposure quantity of other portions.
The following problems, however, arise, in the technique stated in the above Publication.
First, when the reticle itself is provided with a light reducing or light attenuating characteristic, the number of steps of manufacturing the reticle increases, and a burden on the reticle manufacturing steps augments, increasing the possibility in which a pattern defect is produced during the manufacturing process. On the other hand, when using the filter to be overlapped with the reticle, there increases such a possibility that the reticle is damaged and contaminated by attaching and detaching the filter. Thus, problem is produced in terms of a maintenance and management of the reticle. Further, a dedicated filter is required to be prepared per reticle, and labors needed for manufacturing, maintaining and managing the filter are not ignorable.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an exposure apparatus and a field stop that are capable of obtaining an ideal light reducing characteristic on an original plate without necessities for giving a light reducing characteristic to the original plate itself for transferring a pattern of a reticle or the like and for preparing light reducing members disposed differently for every original plate.
To accomplish the above object, according to one aspect of the present invention, there is provided a projection exposure apparatus for irradiating a reticle disposed in a position substantially conjugate to a field stop with a light beam from a light source through the field stop, projecting an image of the reticle illuminated with the light beam on a first exposure area on a photosensitive substrate through a projection optical system and, at the same time, projecting peripheral portions of the images on a second area adjacent to the first area on the photosensitive substrate while being overlapped with each other. In this projection exposure apparatus, the field stop is constructed of two superposed aperture members composed of light shielding portions for shielding the light beams and first and second apertures each taking a rectangular shape. Corresponding sides of the first aperture and the second aperture are disposed substantially in parallel. The light reducing portions are provided at a selected side of the first aperture in a face-to-face relationship with a selected side among the sides of the second aperture, and in such way that a transmissivity of a light beam becomes smaller from the centers of the first and second apertures toward the light shielding portions. Apertures of each of the two aperture members are combined to provide overlapped rectangular aperture portions, thereby changing a position of a light reducing portion which corresponds to an image peripheral portion.
Further, the two aperture members are relatively moved by a drive system in such directions that the sides of the overlapped aperture portions serving as the light reducing portions are extended during an image projection.
Moreover, a light shielding portion is formed by providing a light shielding material on a transparent substrate. A light reducing portion is formed at a boundary between an aperture and a light shielding portion on the transparent substrate, and so that density of the light shielding material becomes higher from the aperture toward the light shielding portion.
As described above, the field stop involves a combination of two aperture members including light shielding portions formed by providing light shielding material on a transparent substrate, a plurality of apertures and light reducing portions provided at selected sides among the sides of these apertures, and so that density of the light shielding material varies in accordance with distance from the center of an aperture. Hence, there are eliminated problems relative to a burden on manufacturing the reticle when providing the light reducing member on the reticle itself and damage and contamination of the reticle when attaching and detaching a light reducing filter to and from the reticle.
Further, the above two aperture members are combined and, at the same time, relatively moved in such directions that the sides of overlapped aperture portions serving as the light reducing portions are extended, thereby obtaining light reducing areas. It is therefore possible to obtain an ideal light reducing characteristic on the reticle.
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patent: 5184196 (1993-02-01), Nakagawa et al.
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patent: 5329336 (1994-07-01), Hirano et al.
patent: 5335044 (1
Goto Hideji
Hanazaki Noritsugu
Watanabe Tomoyuki
Yanagihara Masamitsu
Nikon Corporation
Sikd-er Mohammad Y.
Vorys Sater Seymour and Pease LLP
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