Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2001-10-15
2004-03-16
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000
Reexamination Certificate
active
06707529
ABSTRACT:
TECHNOLOGICAL FIELD
The present invention relates to an exposure apparatus, an apparatus for manufacturing devices, and a method of manufacturing exposure apparatuses, which are employed in transferring a mask pattern onto a substrate in a lithography process for producing microdevices such as, for example, semiconductor elements, liquid crystal display elements, image pickup elements, or thin film magnetic heads or the like, and are preferably employed when exposure light in the ultraviolet band having a wavelength of approximately 400 nm or less, and particularly when exposure light of the vacuum ultraviolet (VUV) band having a wavelength of 200 nm or less, is employed.
BACKGROUND ART
In exposure apparatuses such as steppers or the like which are employed, for example, in the manufacture of semiconductor devices, in order to provide an increase in the degree of integration or minuteness of the semiconductor devices, an increase in resolution is particularly necessary. This resolution is essentially proportional to the wavelength of the exposure light, so that conventionally the wavelengths of the exposure light were progressively shortened. That is to say, the exposure light employed changed from the g line in the visible band of mercury lamps (wavelength 436 nm) to the i line in the ultraviolet band (wavelength 365 mn), and recently, KrF excimer laser light (wavelength 248 nm) has come to be employed. Additionally, presently, ArF excimer laser light (wavelength 193 nm), F
2
laser light (wavelength 157 nm) and Ar
2
laser light (wavelength 126 nm) are being considered for use. Furthermore, in conventional X-ray lithography research, the use of light having wavelengths of 13 nm, 11 nm, or 7 nm, which are in the so-called extreme ultraviolet (EUV or XUV) band and are close to X-rays, and the use of X-rays having a wavelength of approximately 1 nm, has been considered.
However, when wavelength bands of less than approximately that of ArF excimer lasers, that is to say, the vacuum ultraviolet band (VUV) of approximately 200 nm or less, are employed, absorption occurs as a result of the oxygen in the air, and ozone is produced, and transmittivity declines. In exposure apparatuses which employ ArF excimer laser light, for example, the majority of the gas in the optical path of the exposure light is replaced by nitrogen, so that the so-called nitrogen purge is conducted. Furthermore, at wavelength bands of less than approximately that of the F
2
laser, absorption occurs even with nitrogen. In this case, if the region of nitrogen passage is an extremely narrow region, the amount of absorption is slight, and no obstacle is presented to exposure; however, with a long optical path, the amount of light is reduced, and proper amounts of exposure can not be obtained. When light in a wavelength band shorter than the wavelength of the ArF excimer laser (less than approximately 190 nm) and particularly when light in the wavelength band of less than approximately the wavelength of the F
2
laser, is employed, then it is necessary either to replace the majority of gas of the optical path of the light with another gas which allows transmission of light (an inert gas other than nitrogen), or to provide a vacuum.
On the other hand, when the exposure light passes an illumination optical system or optical elements, such as lenses and mirrors, within a projection optical system, then there is absorption of the beat energy by these optical elements as well. When the optical elements experience thermal expansion as a result of the heat energy absorbed in this way, this leads to degradation in image formation characteristic, such as changes in magnification, focal shift displacement, or the like. In order to prevent this degradation in image formation characteristic, conventionally, waste heat treatment was conducted, in which temperature controlling gases were caused to flow in predetermined spaces between lenses, and the side surfaces of lenses or the rear surfaces of mirror or the like were subjected to air cooling or liquid cooling, Recently, requirements have also increased with respect to stability of the image formation characteristic, so that an even higher level of treatment is required with respect to this waste heat treatment as well.
As described above, in exposure apparatuses, when exposure light in a wavelength band of approximately 190 nm or less is employed, it is desirable that the gas of the majority of the optical path be replaced with a gas having an absorption ratio smaller than nitrogen, or that this be made a vacuum. However, when the latter is done and the majority of the optical path is made into a vacuum, the manufacturing costs of the exposure apparatus increase, and the throughput of the exposure apparatus declines. Furthermore, in the exposure apparatus, it is desired that the heat energy of the exposure light be more efficiently exhausted.
In order to simultaneously address these problems, a gas may be supplied to the majority of the optical path of the exposure light, which gas is inert and has a high transmittivity and has good thermal conductivity (in other words, has a low atomic weight), and which is temperature controlled. Currently, the most highly functional gas for use as this type of inert gas having good thermal conductivity, and which is moreover stable, is helium (He). However, helium is present in the earth's crust and in the atmosphere at an extremely low rate, and is high in cost, so that as the amount thereof used increases, the operational cost of the exposure apparatus rise greatly, and this is undesirable. Furthermore, because helium has a low atomic weight, it tends to leak from the gaps in the cover and the like which enclose the optical path of the exposure apparatus, and this presents a problem in that if helium is simply circulated within the cover, the amount of helium progressively decreases.
In view of these points, the present invention has as an object thereof to provide an exposure apparatus and a apparatus for manufacturing devices which, in the case in which a gas having a high transmittivity (inert) and having good thermal conductivity is supplied to at least a portion of an optical path of an exposure energy beam (exposure light), are capable of controlling the amount of this gas which is employed.
Furthermore, as described above, in the exposure apparatus, when exposure light having a wavelength of approximately 200 nm or less is employed, if the optical path of the exposure light is not made into a vacuum, it is necessary to replace the majority of the optical path of the exposure light with a gas having good transmittivity (such as nitrogen or the like). Furthermore, even where the wavelength is within a range of 250-200 nm, in order to obtain good transmittivity, it is desirable that the optical path of the exposure light be replaced with nitrogen or the like.
In connection with this, because the exposure apparatus is usually stored within a box shaped chamber having good airtightness and in order to conduct the positioning of reticles or wafers or the like in a highly precise manner in the exposure apparatus, a stage system, in which movement is conducted along a guide surface in the manner of an air bearing without contact, is provided. For this reason, when this type of stage system is employed, the compressed air sprayed along the guide surface leaks out into the chamber, and this air mixes with the gas having good transmittivity, such as nitrogen or the like, of the optical path of the exposure light, so that a problem is caused in that the transmittivity with respect to the exposure light progressively decreases. When the transmittivity decreases in this manner, the illumination intensity on the wafer decreases, so that in order to obtain the proper amount of exposure, it is necessary to lengthen the exposure period, and thus the throughput of the exposure process declines in an undesirable manner.
Furthermore, in the exposure apparatus, in addition to the stage system, equipment is provided for conducting positioning or
Aoki Takashi
Owa Soichi
Shiraishi Naomasa
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
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