Photography – Camera shake sensing – With accelerometer
Reexamination Certificate
2001-03-26
2003-05-27
Rutledge, D. (Department: 2851)
Photography
Camera shake sensing
With accelerometer
C250S492100, C430S311000, C355S067000
Reexamination Certificate
active
06571057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical instrument having a plurality of spaces formed in the optical path of energy beams, and a gas replacement method and cleaning method thereof. More specifically, the present invention relates to an optical instrument used for an exposure apparatus for manufacturing electronic devices such as semiconductor devices, liquid crystal display devices, imaging devices (CCD or the like), and thin film magnetic heads, and a gas replacement method and a cleaning method of the optical instrument. The present invention also relates to an exposure method using the exposure apparatus and a manufacturing method for devices.
2. Description of the Related Art
When semiconductor devices or liquid crystal display devices are manufactured by a photolithography process, a reduction projection exposure apparatus is used, wherein a pattern image of a reticle is reduced in size and projected onto each projection (shot) area on a wafer, on which a photosensitive material (resist) is applied, via a projection optical system. The circuit in the semiconductor device is transferred by exposing the circuit pattern onto a wafer by the projection exposure apparatus, and is formed by post-processing. Integrated circuits are obtained by laminating the circuit wiring formed in this manner repeatedly, for example, through 20 layers.
Recently, integrated circuits have been integrated in high density, that is, miniaturization of circuit patterns has been advanced. Therefore, the exposure light used for the projection exposure apparatus also tends to have a short wavelength. That is to say, a KrF excimer laser (&lgr;=248 nm) is now being used, instead of the bright-line of a mercury lamp which has heretofore been the mainstream, and implementation of an ArF excimer laser (&lgr;=193 nm) having a shorter wavelength is now entering the final stage for practical use. Moreover, research of an F
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laser (&lgr;=157 nm) has been made, aimed at further high-density integration.
In general, ultraviolet radiation having a wavelength of about 190 nm or less is referred to as vacuum-ultraviolet light, and is not transmitted through the air. This is because light is absorbed by substances such as oxygen molecules, water molecules, and carbon dioxide molecules contained in the air (hereinafter referred to as “light-absorbing substances”). Accordingly, with exposure apparatus using the vacuum-ultraviolet light, light-absorbing substances in the exposure optical path should be reduced or eliminated, in order that the exposure light reaches the wafer face with sufficient illuminance.
Moreover, with an exposure apparatus using the KrF excimer laser beam or the ArF excimer laser beam, there is a problem of a phenomenon referred to as “clouding” of optical members. This is a phenomenon where contaminants adhere to the optical member and cause absorption. Due to this “clouding”, it becomes difficult for exposure light having sufficient illuminance to reach the wafer, thereby decreasing the throughput. As the contaminants causing “clouding”, there can be considered halides such as plasticizers contained in the covering material of electric wires, exposed to the space where the exposure optical path is formed, organic substances such as machine oil adhered to members constituting the apparatus, or organic substances contained in adhesives or the like.
Currently, measures are taken such that, for non-metal members of the members constituting the exposure apparatus, a substance having less outgassing is used, and for metal members, a substance having low surface roughness is used, the machine oil is completely removed by means of ultrasonic cleaning or the like, and these members are stored in a closed space purged by dry nitrogen. However, it is not easy to prevent outgassing completely, nor to remove the “clouding” completely, and contaminants causing “clouding” adhere to the optical members even during assembly of the apparatus or during operation (during shading pattern exposure).
Therefore, in order to irradiate the exposure light stably onto the substrate, it is necessary to eliminate the light-absorbing substances from the exposure optical path all the time, and to regularly clean the optical members.
With a conventional exposure apparatus, in order to make the exposure light reach the substrate with sufficient illuminance and uniformly, efforts have been made involving replacing the inside of the exposure optical path with low absorbent gas having little energy absorption of vacuum-ultraviolet light, to thereby reduce the light-absorbing substances in the exposure optical path. However, in the case of optical instruments using vacuum-ultraviolet light, since the light is apt to be absorbed by the light-absorbing substances, as described above, it is necessary to keep the concentration of light-absorbing substances contained in the gas within the exposure optical path as low as possible, for example, less than about several ppm. The replacement gas is generally expensive, and the consumption thereof is a problem associated with the running cost of the apparatus. With optical instruments using vacuum-ultraviolet light, since all of a plurality of spaces forming the exposure optical path must be subjected to the gas replacement, the running cost for the gas replacement is large, and its reduction is an important problem. Moreover, in order to replace all the spaces with the replacement gas effectively, without decreasing the operating ratio of the apparatus, it is necessary to reduce the light-absorbing substances in the individual spaces within as short a time as possible. Furthermore, since the rate at which the light-absorbing substances are generated and the inflow quantity are different for each individual space, it is necessary to take measures depending on these spaces.
Also, there has heretofore been a technique for removing contaminants adsorbed in the optical members, referred to as optical cleaning (or light ozone cleaning). With optical cleaning, oxygen gas absorbs ultraviolet light, and is excited to become ozone. Then, the oxygen gas is further converted to oxygen atoms having high reactivity, to react with contaminants adhered to the optical members, and becomes light molecules such as water, carbon dioxide, and is removed. From research up to now, it is known that optical cleaning has low effectiveness where there are no oxygen molecules (J. Illum. Engng. Inst. Jpn. Vol. 83, Nov. 5, 1999, “Verification of UV/03 Cleaning Using Xe
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Excimer Lamp”). Since the absorption cross section (absorption coefficient) of substances in the vacuum-ultraviolet light is larger than the case of ultraviolet light having a longer wavelength, it is obvious that with an optical instrument using vacuum-ultraviolet light, more reliable measures against “clouding” are required.
However, in the case of light having a low wavelength such as the F
2
laser, since the energy is apt to be absorbed by the light-absorbing substances, if the light-absorbing substances are contained in a large amount in the gas within the exposure optical path, the light hardly reaches sufficiently to the space located away from the light source in the optical path, and hence effective optical cleaning cannot be performed with respect to the optical members. Also, in the case of vacuum-ultraviolet light, there is the contradiction that, in order to transfer a pattern with sufficient light volume, it is necessary to eliminate the oxygen molecules, which are light-absorbing substances, but oxygen molecules are necessary for the optical cleaning.
As described above, the vacuum-ultraviolet light is difficult to handle, and considerable labor is required for keeping cleanliness. Consequently, a cost increase, and a decrease in throughput cannot be avoided.
In view of the above situation, it is a primary object of the present invention to provide an optical instrument which can reduce the concentration of light-absorbing substances and the concentration non
Nikon Corporation
Oliff & Berridg,e PLC
Rutledge D.
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