Optical member of synthetic quartz glass for excimer lasers and

Details Optical member of synthetic quartz glass for excimer lasers and Optical member of synthetic quartz glass for excimer lasers and

1993-05-15

1994-11-15

Bell, Mark L.

Glass manufacturing

Processes

With shaping of particulate material and subsequent fusing...

65DIG8, 501900, 501 54, C03C 306

Patent

active

053644336

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a synthetic quartz glass optical member which is very stable against irradiation with ultraviolet laser beams having oscillation wavelengths of not more than 300 nm and a method for producing the same and more specifically to an optical member of synthetic quartz glass which is very stable against irradiation with KrF excimer laser beams and ArF excimer laser beams and a method for producing the same.
The present invention further pertains to a method for producing a quartz glass member suitably used as an optical members such as a window, a mirror, a lense and a prism which constitute an optical system of a lithography device provided with, in particular, an excimer laser as a light source and used for producing semiconductor chips.


BACKGROUND ART

Along with a recent increase in the degree of integration of LSI's, these has been required a technique which permits display of accurate images, for instance, with minute lines of a width on the order of submicrons in a photolithography technique or a lithography technique for displaying an integrated circuit patter on a wafer. In the photolithography technique, an attempt has accordingly been done to adopt light rays of short wavelengths as light sources for exposure systems in order to form accurate images by lines having such a quite narrow width. There have been required, for instance, a stepper lense for lithography to have excellent transparency to ultraviolet rays, uniform refractive index distribution for ultraviolet rays, in particular, ultraviolet laser beams and high durability to the irradiation of ultraviolet laser beams in order to display, on a wafer, accurate and clear distortion-free images of integrated circuit patterns by fine lines without light and dark irregularities.
However, a lense made from a conventional optical glass currently used has very low transmittance to ultraviolet rays. For instance, when using ultraviolet rays having wavelengths falling within the wavelength range shorter than 365 nm (i-ray), the transmittance to ultraviolet rays is abruptly reduced during operating the optical system and it is thus substantially impossible to use such a lense as a stepper lense. In particular, when using ultraviolet rays having wavelengths falling within the wavelength range shorter than 365 nm (i-ray), the lense generates heat through absorption of the irradiated ultraviolet rays. This leads to changes of optical characteristics of the optical lense and in turn becomes a cause of a deviation of the focal length thereof. For this reason, quartz glass has been used as a material for producing parts through which ultraviolet rays are transmitted.
However, the quartz glass made of a naturally-occurring rock crystal has a low transmittance to ultraviolet rays having wavelengths of not more than 250 nm, further begins to absorb lights in the ultraviolet region during irradiation with ultraviolet rays and the ultraviolet transmission rate thereof is further reduced. It has thus been substantially impossible to use such quartz glass as a material for producing a stepper lense. It is believed that the quartz glass made of a naturally-occurring rock crystal absorbs light rays in the ultraviolet region due to impurities present in the quartz glass and for this reason, synthetic quartz glass having a low impurity-content, i.e., synthetic silica glass has been used for producing optical members which are used in the ultraviolet region.
In order to prevent any contamination with metallic impurities, the presence of which in general becomes a cause of the ultraviolet absorption, the synthetic quartz glass has been prepared by directly introducing, into an oxyhydrogen flame, vapor of a volatile, highly pure silicon compound which is chemically synthesized and purified through distillation, for instance, a silicon halides such as silicon tetrachloride (SICl.sub.4); an alkoxysilane such as ethoxysilane (Si(OC.sub.2 H.sub.5).sub.4), methoxysilane (Si(OCH.sub.3).sub.4) or the like; or an alkylalkoxysilane

REFERENCES:
patent: 4317668 (1982-03-01), Susa et al.

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