Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-10-19
2002-09-17
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S905000
Reexamination Certificate
active
06451719
ABSTRACT:
FIELD OF APPLICATION
The present invention relates to a silica glass optical material and a method for producing the same; in particular, it relates to a silica glass optical material for radiation with a wavelength of 155 to 195 nm using an excimer laser or an excimer lamp as the light source, and to a method for producing the silica glass optical material.
PRIOR ART
The silica glass optical material described above is used as lenses, prisms, windows, reflectors, photomasks, tubes, etc., that are embedded in a light irradiating device for photo-cleaning, aligners for producing integrated circuits (photolithographic devices), etc., using an excimer laser device or an excimer lamp which emits light with a wavelength of from 155 to 195 nm.
Conventionally, for producing patterns of integrated circuits on a silicon wafer, ultraviolet radiation using mercury vapor lamp, such as g-line and i-line, has been used as the light source for a photolithographic device. However, as the semiconductor devices become finer, the aforementioned g-line and i-line found limits in resolution. Accordingly, excimer lasers which emit radiation with shorter wavelength attracted attention, and a photolithographic device using KrF excimer laser (248 nm) has been developed and put into practice.
However, a higher degree of integration of the semiconductor devices is expected in the near future, and this requires a light source capable of producing fine patterns with a line width of 0.1 &mgr;m or still finer.
As the light sources meeting the requirements above, there can be mentioned high power output vacuum ultraviolet radiators emitting a wavelength of from 155 to 195 nm. Thus, efforts are devoted mainly to the development of an ArF excimer laser (193 nm), and next to that of an ArCl excimer laser (175 nm), an F
2
excimer laser (157 nm), etc. However, because the high power output vacuum ultraviolet radiation is far higher in power compared to the ultraviolet radiation used conventionally in photolithographic devices, the optical materials subjected to the irradiation may suffer abrupt damage such as a drop in transmittance, an increase in refractive index, a generation of strain, a generation of fluorescence, occasional generation of micro-cracks, etc., thereby making the material practically unfeasible.
In addition to the above, dry cleaning using a high power output ultraviolet radiation with a wavelength of from 155 to 195 nm, such as an ArF excimer laser (193 nm), an F
2
excimer laser (157 nm), an Xe
2
excimer lamp (172 nm), an ArCl excimer lamp (175 nm), etc., is being developed as a method for cleaning semiconductor devices. However, devices for the cleaning treatment require a large optical material for use as the windows and tubes. However, if the optical material becomes larger in size, it tends to suffer greater damage by the high output vacuum ultraviolet radiation, and it no longer serves as an optical material.
In the light of such circumstances, the development of an optical material that suffers less damage by the irradiation with the aforementioned high power output vacuum ultraviolet radiation emitted by an excimer laser or an excimer lamp has been keenly demanded.
As a material that satisfies the aforementioned requirements, there is known a material disclosed in Japanese Patent Laid-Open No. 227827/1994. More specifically, the optical material disclosed in the publication above is a transparent quartz glass produced by heating a porous quartz glass body formed by depositing fine quartz glass particles obtained by flame hydrolysis and growing it, characterized in that the transparent quartz glass contains 10 ppm or less of OH, 400 ppm or more of a halogen, and that it contains hydrogen.
In Japanese Patent Publication No. 48734/1994 an optical material for laser radiation is proposed, having a gaseous hydrogen concentration of at least 5×10
16
(molecules/cm
3
) or higher and an OH group concentration of 100 wtppm or higher. Further, in Japanese Patent Publication No. 27013/1994 a synthetic silica glass optical body is proposed having a hydrogen gas concentration of at least 5×10
16
(molecules/cm
3
) or higher, an OH group concentration of 50 wtppm or higher, and substantially free from distribution in fluctuation of refractive index by canceling out the distribution in fluctuation of refractive index based on the concentration distribution of OH groups by the distribution in fluctuation of refractive index based on the virtual temperature.
However, if the optical material is used in a large optical device, for instance, in an optical device exceeding a size of 200 mm in diameter and 30 mm in thickness, non-uniform distribution likely occurs in the concentration of hydrogen molecules, OH Ad groups, and halogen, and this leads to inferior optical characteristics ascribed to the change in transmittance and refractive index under irradiation with excimer laser or excimer lamp. If OH groups should be contained in the silica glass optical material in such a high concentration as 100 wtppm or higher, the durability becomes inferior due to a drop in the initial transmittance in the vacuum ultraviolet region. That is, the optical material proposed in the above patent publication suffered problems of low initial transmittance in the wavelength region of from 1 55 to 195 nm and of insufficient durability. The optical material disclosed in Japanese Patent Laid-Open No. 227827/1994 utilizes halogens, however, among the halogens, Cl and the like are apt to generate defects upon irradiation of an ultraviolet radiation, and it suffered a serious problem of deteriorating the performance of the optical material such as transmittance in the targeted spectral region.
SUMMARY OF THE INVENTION
In the light of such circumstances, it has been found that there can be obtained a synthetic silica glass optical material excellent in durability to long irradiation with an excimer laser or excimer lamp and having high transmittance and a small fluctuation in refractive index, &Dgr;n, by increasing the purity of the optical material higher than that disclosed in the published patent application above while controlling the concentration of the OH groups and the hydrogen molecules in a certain range, and by making the concentration distribution thereof uniform while particularly selecting Fluorine among the halogens and controlling the concentration thereof to a specified range smaller than that employed in a conventional technology. Furthermore, by limiting the concentration of the OH groups and the hydrogen molecules within the synthetic silica glass optical material in a range narrower than that described above, it has been found that the material can yield a higher initial transmittance, particularly, with respect to an excimer laser radiation in the wavelength region of from 155 to 195 nm, and that the durability can be maintained at a high level. The present invention has been accomplished based on these findings.
That is, an object of the present invention is to provide a silica glass optical material having a high initial transmittance with respect to excimer lasers and excimer lamps emitting radiation in a wavelength region of from 155 to 195 nm and a small fluctuation in refractive index, yet having excellent durability when subjected to an irradiation for a long duration of time.
The problems above can be solved by one of the embodiments described in (1) to (13) below.
(1) A silica glass optical material for transmitting light with a wavelength of from 155 to 195 nm emitted from an excimer laser or an excimer lamp, wherein said silica glass optical material is of ultrahigh purity, contains from 1 to 1 00 wtppm of OH groups, from 5×10
16
to 5×10
19
molecules/cm
3
of H
2
, and from 10 to 10,000 wtppm of F, but is substantially free from halogens other than F, and has a fluctuation in refractive index, &Dgr;n, of from 3×10
−6
to 3×10
−7
.
(2) A silica glass optical material of (1) above, wherein the fluctuation in OH-group concentration, &Dgr;OH, is 30 w
Heraeus Quarzglas GmbH & Co. KG
Milde & Hoffberg LLP
Sample David
LandOfFree
Silica glass optical material for excimer laser and excimer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silica glass optical material for excimer laser and excimer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silica glass optical material for excimer laser and excimer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2896702