Glass manufacturing – Processes – With chemically reactive treatment of glass preform
Reexamination Certificate
1999-07-06
2001-08-07
Derrington, James (Department: 1731)
Glass manufacturing
Processes
With chemically reactive treatment of glass preform
C065S031000, C065S061000, C065SDIG008, C065S033200, C264S001230, C264S001240, C264S001320, C264S001330, C264S001380
Reexamination Certificate
active
06269661
ABSTRACT:
This application claims the benefit of Japanese patent application No. 08-259948, filed Sep. 30, 1996, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Present Invention
The present invention relates to an optical component, for example, a lens or a mirror, which is used in optical systems in a wavelength region of 400 nm or less (preferably 300 nm or less, such as an optical component for use in photolithography) and a method for manufacturing the same. More particularly, the present invention relates to a method of manufacturing optical components for use in UV photolithography that show a reduced surface loss in the UV region. The present invention improves the performance of the illumination lenses and projection lenses used in KrF and ArF excimer laser steppers using ultraviolet light sources with a wavelength of 300 nm or less.
2. Discussion of Related Art
An exposure apparatus known as a stepper has been used in photolithographic techniques where fine patterns of integrated circuits are exposed and transferred onto wafers made of semiconductors such as, for example, silicon. As Large Scale Integrated Circuits (LS's) have become more highly integrated in recent years, the light sources used in such steppers have shifted to shorter wavelengths, i.e., from the g line (436 nm) to the i line (365 nm). More recently, the steppers have shifted to even shorter wavelengths, such as KrF (248 nm) and ArF (193 nm) excimer lasers.
Generally, the lens materials used In the illumination lenses or projection lenses of steppers consist mainly of optical glass with a high transmittance of the i line. On the other hand, in the case of KrF and ArF excimer lasers, synthetic fused silica and fluoride single crystals such as CaF
2
(fluorite) are used instead of conventional optical glass.
Such optical components generally must have a transmittance of 99.5% or greater in the wavelength region used. Furthermore, a reduction of surface loss also is an especially important quality requirement in optical components.
It has been found that for optical components used in a short wavelength region of 300 nm or less, the surface loss cannot be reduced to 0.5% or less using conventional polishing methods or cleaning methods. As a result of long years of diligent research concerning the causes of this problem, the present inventors have ascertained the following facts:
(1) Surface loss includes loss other than scattering caused by the surface roughness.
(2) Some surface loss is caused by the absorption of metal residues, such as, for example, polishing agents.
Over a period of many years, the present inventors have conducted experiments in order to verify the above-mentioned facts.
A method using a low-pressure mercury lamp made of synthetic fused silica as a light source is generally known as an ultraviolet cleaning method. This light source emits ultraviolet light at 185 nm and 254 nm. Since the energy of this light source is greater than the bonding energy of most organic compounds, chemical bonds are broken when this energy is absorbed by organic substances, so that radicals and molecules in an excited state can be generated. Ultraviolet light at 185 nm is absorbed by oxygen molecules so that O
3
is generated. O
3
absorbs ultraviolet light at 254 nm and generates active oxygen. This active oxygen reacts with the radicals and excited molecules of organic substances, so that the organic substances are decomposed.
In order to obtain an optical material that has an internal transmittance of 99.5% or greater, it is necessary to manufacture a material that contains few impurities or structural defects that cause internal absorption in the optical material. Accordingly, synthesis by flame hydrolysis is used as a method for manufacturing synthetic fused silica with few impurities or structural defects. In this method, an Si compound gas (which serves as a raw-material gas), a carrier gas, which transports the Si compound gas, and gases which are used for combustion/heating (e.g., H
2
, O
2
gas, etc.), are caused to jet from a burner, and fine particles of SiO
2
that are produced in the flame are deposited on a target and simultaneously vitrified.
With respect to fact (1) discussed above, the relationship between surface roughness and transmittance was confirmed.
FIGS. 1 and 2
show the respective relationships between surface roughness and the measured transmittance of experimentally manufactured optical components (&phgr;60×t 10 mm parallel flat plates) at measurement wavelengths of 248 nm and 193 nm. Synthetic fused silica, which were all manufactured under identical conditions, were used as the measurement. Furthermore, the surface roughness was measured using an optical interference type surface roughness meter.
As shown in
FIGS. 1 and 2
, although the transmittance depends to a certain extent on the surface roughness, i.e., on the surface scattering loss, other factors also have an effect on the transmittance value.
This further shows that in addition to surface scattering, surface loss caused by absorption also largely influences the measurement of transmittance. It is thought that this absorption is caused by structural defects resulting from residual impurities and residual stress.
Even in cases where almost no metallic impurities such as CeO
2
are detected and the surface roughness is less than 1 Å RMS, the transmittance may still be lowered 0.5% or more compared to a theoretical transmittance. Thus, a problem remains.
SUMMARY OF THE PRESENT INVENTION
Accordingly, the present invention is directed to a method of manufacturing optical components for use in the ultraviolet region that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.
In one aspect of the present invention there is provided a method for manufacturing an optical component including the steps of cutting out a part from a block material, polishing optical sides of the part, subjecting the part to heat treatment at a temperature of 100 to 900° C., and subjecting the part to acid treatment.
In a second aspect of the invention, there is provided a method for manufacturing an optical component including the steps of cutting out a part from a block material, polishing optical sides of the part, subjecting the part to acid treatment, and subjecting the part to heat treatment at a temperature of 100 to 900° C.
In a third aspect of the invention, there is provided a method for manufacturing an optical component including the steps of cutting out a part from a block material, polishing optical sides of the part, subjecting the part to acid treatment, subjecting the part to an ultraviolet treatment, and subjecting the part to heat treatment at a temperature of 100 to 900° C.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Additional features and advantages of the present invention will be set forth in the description which follows, and will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure and process particularly pointed out in the written description as well as in the appended claims.
REFERENCES:
patent: 4427500 (1984-01-01), Platzer
patent: 4911743 (1990-03-01), Bagby
patent: 5133791 (1992-07-01), Yagami et al.
patent: 5776219 (1998-07-01), Jinbo et al.
patent: 5983672 (1999-11-01), Jinbo et al.
patent: 2 065 097 (1981-06-01), None
patent: 58-171 004 (1983-10-01), None
patent: 60-131 850 (1985-07-01), None
patent: 63-107 842 (1988-05-01), None
patent: 7-120 633 (1995-05-01), None
patent: 1 295 352 (1987-03-01), None
European Search Report (Feb. 19, 1998).
Jinbo Hiroki
Komine Norio
Moriya Akiko
Derrington James
Morgan & Lewis & Bockius, LLP
Nikon Corporation
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