Synthetic silica glass used with uv-rays and method producing th

Details Synthetic silica glass used with uv-rays and method producing th Synthetic silica glass used with uv-rays and method producing th

1999-01-14

2000-11-07

Bell, Mark L.

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

65 176, 65 321, 65 325, 65 67, C03C 306, C03B 910, C03B 1914, G02B 100

Patent

active

061436763

DESCRIPTION:

BRIEF SUMMARY
INDUSTRIAL FIELD OF APPLICATION

The present invention relates to a synthetic silica glass optical material for use with a high power vacuum ultraviolet rays; in further detail, it relates to an optical material for use as lenses, prisms, windows, reflectors, tubes, etc., which are assembled in an irradiation apparatus using high output power vacuum ultraviolet rays as the light source, such as excimer lasers, excimer lamps, etc., having a wavelength in a range of from 165 to 195 nm.


PRIOR ART

Ultraviolet rays using mercury vapor lamp, such as g-rays and i-rays, have been used heretofore for the light source of photolithography apparatus for patterning electronic circuit patterns on silicon wafers. With increasing fineness in semiconductor devices, however, the aforementioned g-rays and i-rays had limits in increasing resolution. Accordingly, excimer lasers having shorter wavelength had attracted more attention and led to the development of an apparatus for photolithography using a KrF excimer laser. This apparatus is already put into practical stage. Still, however, the degree of integration in semiconductor devices is expected to further increase, and a light source capable of patterning fine patterns 0.2 mm or less in line width is required. Such light sources capable of achieving the requirements are expected to include high output power vacuum ultraviolet rays in the wavelength range of from 165 to 195 nm, for instance, with the principal example being an ArF excimer laser (193 nm), a Xe.sub.2 excimer laser (172 nm), an ArCl excimer laser (175 nm), a Xe.sub.2 excimer lamp (172 nm), and an ArCl excimer lamp (175 nm), and their development are already under way. However, because the aforementioned high output power vacuum ultraviolet rays are even higher in output power than the ultraviolet rays used in conventional apparatuses of photolithography, the optical materials subjected to the irradiation therefrom suffers an abrupt occurrence of severe damage such as a drop in transmittance, an increase in refractive index, and a generation of deformation, as to make the optical material practically unfeasible.
Furthermore, at present, dry cleaning for semiconductor devices using high output power vacuum ultraviolet rays in the wavelength range of from 165 to 195 nm, for instance, an ArF excimer laser (193 nm), a Xe.sub.2 excimer laser (172 nm), an ArCl excimer laser (175 nm), a Xe.sub.2 excimer lamp (172 nm), and an ArCl excimer lamp (175 nm), is under development for use as a cleaning method for semiconductor devices. Such cleaning apparatuses require large optical materials for use as windows and tubes. However, with increasing size of optical materials, the damage attributed to high output power vacuum ultraviolet rays also increase as to make the use of the optical materials practically unfeasible. Conventional large silica glasses had limits in practically available size, because they were produced by first preparing a synthetic silica glass ingot by means of either direct method, comprising introducing a high purity silicon compound into an oxyhydrogen flame to effect hydrolysis and directly depositing the thus obtained fine particles of glass on a target; or VAD method, comprising vitrifying and solidifying, in an electric furnace under vacuum, a white-colored opaque soot body prepared by hydrolyzing a high purity silicon compound using an oxyhydrogen flame. The synthetic silica glass ingot thus obtained was then shaped by hot pressing in a vacuum electric furnace using a graphite mold frame, cut into thin-layered sheet materials, and polished. Furthermore, the silica glass sheet material obtained by direct method above contained OH groups at such a high concentration in the range of from 400 to 1000 wt ppm, and suffered damages when subjected to the irradiation of high output power vacuum ultraviolet rays for a long duration of time. That is, optical transmittance decreased due to solarization. Moreover, because ingots were formed into sheets, the content of OH groups fluctuated as such that the f

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