Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Reexamination Certificate
1999-07-08
2002-03-05
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
C065S414000, C065S421000
Reexamination Certificate
active
06351972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synthetic fused silica member and a method for producing the same, as well as an optical member for excimer laser. In particular, the present invention relates to a synthetic fused silica member that can suitably be used for optical applications utilizing as a light source high energy ultraviolet rays such as those from excimer lasers, typically KrF and ArF excimer lasers, for example, use as a lens material for steppers and a synthetic fused silica material for photomasks, and a method for producing such a synthetic fused silica member, as well as an optical member for excimer laser produced from the synthetic fused silica material such as lenses, mirrors and photomasks.
2. Description of Related Art
With recent use of higher integration degree of semiconductor devices, in particular, VLSIs, the circuit pattern has rapidly become finer. Therefore, the wavelength and illuminance of light sources for the VLSI production are becoming shorter and stronger, respectively.
On the other hand, synthetic fused silica, which shows good performance in the ultraviolet range, has been getting importance as not only a material for photomasks but also a material for optical members such as lenses and mirrors in optical systems of light exposure apparatuses.
Such synthetic fused silica members are produced by, for example, vaporizing a raw material silane compound, hydrolyzing or oxidizing by combustion the vaporized silane compound in oxyhydrogen flame to form silica microparticles so that the silica microparticles should deposit on a rotating refractory carrier, and melting the silica microparticles during the deposition.
However, when a synthetic fused silica member produced from such a material is irradiated by a high energy ultraviolet light such as those from excimer lasers, it may emit yellow fluorescence at a wavelength of 560-580 nm. Therefore, when such a member is used for optical applications utilizing ultraviolet lights such as those from excimer lasers as a light source, for example, used as a lens for stepper, a material of photomask substrate or the like, it may cause a problem of light exposure of resists and the like. Accordingly, it may be unsuitable for use as a lens of stepper or the material of photomask substrate.
SUMMARY OF THE INVENTION
The present invention has been accomplished from the viewpoint of the above technical circumstance, and its object is to provide a synthetic fused silica member that does not emit yellow fluorescence at a wavelength of 560-580 nm even when irradiated with an ultraviolet light by an excimer laser or the like, and therefore can be suitably used for optical applications utilizing ultraviolet lights such as those from excimer lasers as a light source, for example, use as a lens material for stepper or the like. It is also an object of the present invention to provide a method for producing the aforementioned synthetic fused silica member, and an optical member for excimer laser produced from the aforementioned synthetic fused silica member, for example, a lens, photomask and the like.
The inventors of the present invention earnestly conducted studies in order to achieve the aforementioned object. As a result, it was found that sulfur impurities such as SCl
2
and S
2
Cl
2
contained in the raw material silane compound caused the yellow fluorescence emission at a wavelength 560-580 nm of the synthetic fused silica member upon ultraviolet irradiation. That is, such sulfur impurities contained in the raw material silane compound are simultaneously vaporized when the silane compound is vaporized, and introduced into the oxyhydrogen flame together with the silane compound gas. In this case, the sulfur impurities are taken into the synthetic fused silica, which is considered to be inherently likely to incorporate sulfur compounds due to its structural characteristics. As a result, the synthetic fused silica member emits yellow fluorescence at a wavelength of 560-580 nm upon ultraviolet irradiation. The inventors of the present invention accomplished the present invention based on this finding.
That is, the present invention provides a method for producing a synthetic fused silica member comprising vaporizing a raw material silane compound, hydrolyzing or oxidizing by combustion the vaporized silane compound in oxyhydrogen flame to form silica microparticles so that the silica microparticles should deposit on a rotating refractory carrier, and melting the silica microparticles during the deposition to form the synthetic fused silica member, characterized in that sulfur impurities are preliminarily removed from the raw material.
If the causative substances of the aforementioned yellow fluorescence, i.e., the sulfur impurities, have been preliminarily removed from the raw material as in the aforementioned method of the present invention, the sulfur impurities are not introduced into the oxyhydrogen flame together with the silane compound when the silane compound is vaporized. Therefore, the sulfur impurities are not introduced into the produced synthetic fused silica member. As a result, the obtained synthetic fused silica member does not emit yellow fluorescence at a wavelength 560-580 nm even when irradiated with an ultraviolet light by an excimer laser or the like.
The influence of sulfur impurities contained in the raw material silane compound on the synthetic fused silica member has not been considered at all so far. Therefore, the sulfur impurities have not been preliminarily removed from the material in any conventional methods.
In the aforementioned method for producing a synthetic fused silica member according to the present invention, the sulfur impurities are preliminarily removed from the raw material preferably to a level of 10 ppm or less.
If the sulfur impurities are preliminarily removed from the material to a level of 10 ppm or less, a significant amount of sulfur impurities that may cause the problem are not introduced into the synthetic fused silica member, and therefore the synthetic fused silica member does not emit yellow fluorescence at a wavelength 560-580 nm even when irradiated with an ultraviolet light by an excimer laser or the like.
In the method for producing a synthetic fused silica member according to the present invention, the sulfur impurities are preferably sulfur chlorides.
Among the sulfur impurities, sulfur chlorides (e.g., SCl
2
, S
2
Cl
2
), in particular, have a boiling point substantially the same as that of the raw material silane compound. Therefore, among the sulfur impurities, sulfur chlorides are particularly likely to be simultaneously vaporized when the silane compound is vaporized, and introduced into oxyhydrogen flame together with the silane compound. That is, sulfur chlorides are more likely to be incorporated into the synthetic fused silica members compared with other sulfur impurities. Therefore, since sulfur chlorides among the sulfur impurities are particularly likely to cause the yellow fluorescence, it is particularly necessary to preliminarily remove sulfur chlorides.
In the aforementioned method according to the present invention, the silane compound is preferably a compound represented by the formula (1):
R
n
SiX
4−n
(1)
wherein R each represents hydrogen atom or a monovalent aliphatic hydrocarbon group, which may be identical or different, x represents a halogen atom or a group —OR, and n represents an integer of 0-3, or the formula (2):
SixRyOz (2)
wherein R has the same meaning as defined above, x represents an integer not less than 2, y represents a positive integer not more than 2x+2, and z represents a positive integer not more than 2x.
Those silane compounds represented by the aforementioned formulae can easily be obtained as a usual material of synthetic fused silica members, and have widely been used. Therefore, they are preferably used also in the present invention.
The present invention also provides a synthetic fused silica member produced by the aforeme
Hogan & Hartson L.L.P.
Shin-Etsu Chemical Co. , Ltd.
Vincent Sean
LandOfFree
Synthetic fused silica member, method for producing the same... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Synthetic fused silica member, method for producing the same..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Synthetic fused silica member, method for producing the same... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2835802