Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-05-23
2003-03-04
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C359S819000
Reexamination Certificate
active
06529264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projection exposure apparatus which is employed in photolithographic processes to manufacture microdevices such as semiconductor elements, imaging elements, liquid crystal display elements and thin-film magnetic heads.
2. Description of Related Art
In the photolithographic process for the manufacture of semiconductor devices, a pattern on a mask is transferred on to a wafer or glass plate (hereinafter also referred to as a substrate) coated with a photo resist. This type of projection exposure apparatus, a step-and-repeat type exposure apparatus (hereinafter also referred to as a “stepper”), has been widely used in the past. This step-and-repeat type exposure apparatus reduces and projects the pattern of the mask all together on each shot region of the wafer for exposure. When it finishes exposing one shot region, it moves the wafer and exposes the next shot region. It successively repeats this operation. Further, a step-and-scan type exposure apparatus is also being developed which enlarges the exposure range of the mask pattern by limiting the exposure light from an illumination system to a slit shape (rectangular shape), using this slit light to reduce and project part of the mask pattern on to the wafer, and in that state making the projection optical system synchronously scan the mask and wafer. This step-and-scan type exposure apparatus has both the advantages of the transfer system of an aligned which transfers the pattern of the entire surface of a mask on to the entire surface of a wafer by equal magnification by a single scan and exposure operation and the advantages of the transfer system of the above stepper.
In such a conventional projection exposure apparatus, the optical elements constituting the projection optical system are held in a barrel which is fastened to a frame of the exposure apparatus. The conventional means for fastening the barrel had been to bolt a flange formed at its center to the frame. However, the two ends of the barrel were free and there was the problem that the two ends of the barrel would shake due to vibration transmitted from other apparatuses in the clean room where the projection exposure apparatus was installed, for example, fans for control of the temperature and humidity and other sources of vibration. This vibration transmitted from sources of vibration around the projection exposure apparatus was transmitted to the barrel and caused vibration there even if the frequency of the sources of vibration was small since there is a correlation between the natural vibration of the sources of vibration and the natural vibration of the barrel, so the problem of displacement of the optical axis was caused. In particular, when the projection optical system is held by a plurality of barrels like in a reflection and refraction projection system and the plurality of barrels are fastened to the frame, the relative vibration among the barrels has a large effect, so the intervals between the barrels and the relative positions in the direction of rotation change and remarkable deterioration of the imaging characteristics occurs.
Further, the resolution of an exposure apparatus is substantially proportional to the wavelength of the exposure light, so the wavelength of exposure is gradually being made shorter. The exposure light is changing from visible g-ray (wavelength 436 nm) and ultraviolet i-ray (wavelength 365 nm) by a mercury lamp to KrF excimer laser light (wavelength 248 nm). Recently, use of ArF excimer laser light (wavelength 193 nm) and F2 laser light (wavelength 157 nm) has been considered. Here, in the wavelength region lower than that of about ArF excimer laser light, that is, in the vacuum ultraviolet region below about 200 nm, absorption due to oxygen in the air occurs and ozone is produced or substances produced by a photo reaction with the organic substances or moisture in the air deposit on the surface of the optical elements, whereby the transmittance ends up falling. As a measure against this, for example, in an exposure apparatus using ArF excimer laser light, the gas inside the barrels of the projection optical system is replaced with helium (He) or another inert gas, i.e., and so-called purging is performed.
The helium used as the purging gas is highest in performance as an inert and safe gas, but is present in only extremely small amounts in the earth's mantle and atmosphere and therefore is high in price. Further, it is low in atomic weight, so it easily leaks from joints in the barrels of the projection optical system and is consumed in large amounts, therefore increasing the operating cost of the exposure apparatus.
Further, if the wavelength of the illumination light becomes shorter, the types of glass materials able to withstand actual use due to the absorption of light become more limited. If the wavelength becomes less than 300 nm, the only glass materials able to be used in practice at the present time would be fused silica and fluorite. The Abbe numbers of the two are not sufficiently far apart for correction of chromatic aberration, so correction of chromatic aberration would become difficult. As opposed to this, a catadioptric system combining a reflection optical system using a concave mirror etc. and a refraction optical system has been proposed. This catadioptric system can substantially eliminate various types of aberration such as, first and foremost, chromatic aberration, without causing an increase in the number of lenses. In a catadioptric system, however, generally it is necessary to use an optical path deflection member to separate the outbound optical path going toward the concave mirror and the return optical path from the concave mirror. As a result, several optical axes end up present. For this reason, when assembling the catadioptric system, there is the problem that error easily occurs in the adjustment among the plurality of optical axes compared with a refraction optical system.
Further, if the optical path deflection member of the catadioptric projection system tilts (rotational motion), large rotation and distortion of the image occurs. To stably obtain an image of an extremely high resolution, tough requirements are placed on the assembly position of the optical path deflection member. Further, tough requirements are placed on prevention of vibration as well so that the optical path deflection member is held in that position.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide a projection exposure apparatus able to reduce vibration of a barrel structure of a projection optical system and thereby realize good imaging characteristics.
A second object of the present invention is to provide a projection exposure apparatus able to reduce the amount of the inert gas etc. used when supplying said gas to an optical path of the illumination light without causing deterioration of the imaging characteristics.
A third object of the present invention is to provide a projection exposure apparatus able to realize easy adjustment of a plurality of optical axes.
A fourth object of the present invention is to provide a projection exposure apparatus resistant to the occurrence of rotation of the image even when an optical path deflection member tilts and therefore stably giving an extremely high resolution.
1. To achieve the first object, according to the present invention, there is provided a projection exposure apparatus for transferring a pattern of a mask on to a substrate, said projection exposure apparatus comprising a projection optical system having an optical element, a frame for supporting a barrel structure holding the projection optical system, and a support member for supporting the barrel structure at a position different from the frame. The barrel structure may also be a plurality of barrels holding the projection optical system. In the case of a plurality, each barrel may be supported by the frame and the support member. The plurality of barrels for example may includ
Adams Russell
Kim Peter B.
Nikon Corporation
Oliff & Berridg,e PLC
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