Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2000-10-18
2004-05-04
Font, Frank G. (Department: 2877)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000, C355S055000, C355S067000, C355S077000, C250S492200, C430S030000, C430S311000
Reexamination Certificate
active
06731371
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the following priority application is incorporated herein by reference:
Japanese Patent Application No. 11-299331 filed on Oct. 21, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus used in a photolithography process for manufacturing micro devices such as semiconductor circuits, image pick-up devices (such as CCDs), liquid crystal displays, plasma displays, and thin film magnetic heads.
2. Description of the Related Art
In a photolithography process for forming a fine pattern of an electric device such as a semiconductor circuit or liquid crystal display, a projection exposure apparatus such as a stepper is used when transferring an original pattern of a reticle as a mask onto a wafer (or a glass plate) as a substrate to be exposed. In such a projection exposure apparatus, to improve its resolution to address a still finer integration level of micro devices, its exposure wavelength has shifted to a still shorter wavelength region. As the exposure wavelength, 248 nm of a KrF excimer laser is mainly used at present, but a shorter wavelength of about 200 nm or less in the vacuum ultraviolet region has also come to be used. In other words, the 193 nm wavelength of an ArF excimer laser is now virtually in practical use, and a projection exposure apparatus utilizing a laser such an F
1
laser (of 157 nm wavelength) or an Ar
2
laser (of 126 nm wavelength), each having a still shorter wavelength, as an exposure light source is now being developed.
Further, since the resolution can be improved by increasing the numerical aperture (NA) of a projection optical system, a still larger NA of a projection optical system is also being developed. In this connection, because a smaller exposure view field (exposure field) of a projection optical system advantageously affects in realizing a larger NA, the view field of a projection optical system itself is made smaller on one hand and, on the other hand, scanning exposure type exposure apparatuses such as a step-and-scan type exposure apparatus, which secures virtually a large view field by relatively scanning a reticle and a wafer during exposure, are also under practical use.
In a scanning exposure type exposure apparatus, in particular, because each of stages, on which a reticle or a wafer is mounted, should be driven with high precision, an air bearing system, which reduces friction during the movement of the stage by floating the stage by airflow, is adopted as a supporting system for the stage.
In recent years, light of vacuum ultraviolet range has been proposed to be used as exposure light; however, optical materials having practically applicable transmittance relative to vacuum ultraviolet light and usable as a lens or a reticle are limited to synthetic quartz, quartz doped with, e.g., fluorine, and crystals such as fluorite (CaF
2
), magnesium fluoride (MgF
2
), and lithium fluoride (LiF). Further, vacuum ultraviolet light is strongly absorbed by gases on the optical path such as an oxygen gas, moisture, and a hydrocarbonaceous gas (hereinafter, called “absorbent gas”), and, furthermore, evaporated organic substances and the like, which react with vacuum ultraviolet light and result clouding substances on the surface of an optical element, can also be regarded as absorbent gases. Therefore, to exclude those absorbent gases from the optical path of exposure light, the gases on the optical path are required to be replaced with gases such as a nitrogen gas or a rare gas having small absorbency relative to vacuum ultraviolet light (hereinafter, called “transmitting gas”). For instance, with respect to oxygen concentrations, the average concentration should be controlled to a level of ppm order. When the residual concentrations of the absorbent gases does not satisfy such specifications, exposure energy on a wafer considerably decreases, and, as a result, the throughput deteriorates because a longer exposure time is required.
Meanwhile, since in an exposure apparatus, wafers are sequentially exchanged and transferred with a fine pattern, wafers are required to be frequently moved in and out (exchanged) between an inside space including an exposure path and an outside space where the wafers are conveyed. As a result, during the wafer exchange operation, absorbent gases such as an oxygen gas and moisture flow into the inside space along with the conveyed wafers, and easily evaporable organic substances and the like adsorbed on the wafers are also conveyed. Further, because photoresist coated on the wafers itself releases a hydrocarbonaceous gas and the like (outgases), the concentrations of absorbent gases in the optical path cannot be easily kept within a predetermined level with respect to the atmosphere in the vicinity of the wafers.
Also, with respect to an exposure apparatus utilizing vacuum ultraviolet light as its exposure light, when a conventional air bearing system is adopted as a supporting system of a wafer stage and a reticle stage, a large amount of gas is necessary to float the stages. As a result, the gas for floating may flow into the atmospheres, where the stages are positioned, in the vicinity of a wafer and a reticle. If the gas for floating is an absorbent gas as normal atmospheric air, the transmittance of the atmosphere decreases. It is therefore preferable that also as the gas for floating, highly-purified transmitting gas is used. However, there is a problem that, to continuously control the concentrations of absorbent gases in the gas for floating used in relatively high volume within a predetermined level, the associated running costs increase.
Further, with respect to a wafer stage and a reticle stage of an exposure apparatus, their positions are normally measured with high precision by means of laser interferometers. In a laser interferometer, a moving mirror and a fixed mirror are each illuminated with a laser beam, and the position of the moving mirror (movable stage) is measured with reference to the fixed mirror. Also with this case, to improve the measurement accuracy of the laser interferometer, it is preferable, while supplying a transmitting gas on the optical path of exposure light, that the influence of gas fluctuation, accompanying the transmitting gas supply, on the optical path of the laser beams is made as little as possible.
SUMMARY OF THE INVENTION
In view of the above, it is a first object of the present invention to provide an exposure method and an exposure apparatus by which, even when using vacuum ultraviolet light as exposure light, a high exposure light intensity can be obtained by controlling the decrease of transmittance on an optical path.
Further, it is a second object of the present invention to provide an exposure method and an exposure apparatus by which, when adopting an air bearing system as a supporting system of a stage that moves a reticle or a wafer and even when using vacuum ultraviolet light as exposure light, the decrease of transmittance on an optical path can be controlled without increasing operating costs so much.
Further, it is a third object of the present invention to provide an exposure method and an exposure apparatus by which, when measuring, by a laser interferometer, the position of a stage that moves a reticle or a wafer and even when using vacuum ultraviolet light as exposure light, the decrease of transmittance relative to exposure light can be controlled without decreasing the measurement accuracy of the laser interferometer.
Further, it is a fourth object of the present invention to provide an exposure method and an exposure apparatus by which, even in such a case where vacuum ultraviolet light is used as exposure light, the position of a reticle or a wafer can be accurately detected.
Also, it is another object of the present invention to provide a device manufacturing method capable of mass-producing devices with high throughput using such exposure methods above.
A first exposure method according to the present invention is an
Brown Khaled
Font Frank G.
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