Optical: systems and elements – Having significant infrared or ultraviolet property
Patent
1998-04-06
2000-05-16
Chang, Audrey
Optical: systems and elements
Having significant infrared or ultraviolet property
359355, 359361, 355 53, G02B 1314, F21V 520, G03B 2742
Patent
active
060645164
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 Filing of PCT/EP/97/04468 filed on Aug. 15, 1997.
FIELD OF THE INVENTION
The invention relates to an achromatic lens system for ultraviolet rays, a projection exposure system and a method for making optical glass from germanium dioxide.
BACKGROUND OF THE INVENTION
The difficulties of achromatization in the deep ultraviolet are known. Except for quartz glass, essentially only crystalline materials are available. Here, problems are caused by the anisotropy of the crystals which, in addition to the double refraction, also leads to poor manufacturability of polished curved surfaces. In addition, the possible materials are poorly resistant to environmental influences.
This is described in U.S. Pat. No. 5,028,967. Here, as a solution to the problem, the use of SiO.sub.2 glass with GeO.sub.2 admixed (also together with boroxide) is given. What is claimed is a GeO.sub.2 content up to 50 mol %. The example having the highest GeO.sub.2 content has 13.5 mol % GeO.sub.2 and preferably, the content is up to 30 mol %. The deviations of the index of refraction, dispersion and Abbe number compared to pure quartz glass are small. Accordingly, the achromatization is difficult.
The production of amorphous germanium oxide from colorless glass is known per se, for example, from Ullmann's "Encyklopadie der technischen Chemie", 4th edition, Volume 12, Weinheim New York 1985, article "Germanium und Germanium-Verbindungen", pages 221 to 226, key word "Germaniumdioxid", page 225 and from the FR-A 20 18 484 which is cited there (page 1, lines 12 to 19, corresponding search report, as well as title and short analysis of the citation "Secrist and Mackenzie").
In one version, crystalline GeO.sub.2 is generated from GeCl.sub.4 by hydrolysis, melted and rapidly cooled down. This serves as an input material for milling as a powdered catalytic material. From an oxygen plasma having C.sub.2 H.sub.5 OGe, Secrist and Mackenzie allow GeO.sub.2 to deposit onto a cooler base from the gas phase and thereby generate a non-crystalline film.
GeO.sub.2 glass bodies are, however, not known as usable lens blanks.
In the above-mentioned text of Ullmann, key word "Germanate", page 225, optical glasses of germanates, for example, Zn.sub.2 GeO.sub.4, are known which have a high refractive index.
SUMMARY OF THE INVENTION
It is the object of the invention to provide an achromatic lens system having good transmission in the deep ultraviolet (DUV) and a projection illuminating system having such an achromatic lens system. It is intended to provide a glass, which is suitable therefor in combination with quartz glass.
The achromatic lens system for ultraviolet rays of the invention includes: a first lens defining an optical axis and being made of quartz glass or a glass containing mostly quartz; and, a second lens arranged on the axis and being made of glass mostly of germanium dioxide, especially over 70% by weight.
The projection exposure system of the invention includes: a light source having a wavelength of 350 nm or less and defining an optical axis; and, the above achromatic lens system.
The method of the invention is for making optical glass of germanium dioxide and includes the steps of: producing a base body from a highly pure powdered germanium dioxide; depositing amorphous germanium dioxide uniformly onto the base body from a combustion plasma of germanium tetrachloride or germanium tetrahydride with pure oxygen; and, thereafter, rapidly cooling the deposited base body.
With germanium dioxide glass of optical quality, a DUV transparent material is made available which is non-crystalline and therefore shows no polarization effects and can be polarized and is manipulable. In addition, it has a clearly higher dispersion than quartz glass so that the larger converging lenses in the achromatic lens system can be made from the technologically mature quartz glass and the new material is used in the smaller format of the diverging lenses.
In addition, advantageously large differences result with respect to quartz glass with
REFERENCES:
"Consolidation of GeO2 soot body prepared by flame hydrolysis reaction" by S. Sakaguchi, Journal of Non-Crystalline Solids, vol. 171, No. 3, 1994, pp. 228-229.
Carl-Zeiss-Stiftung
Chang Audrey
Ottesen Walter
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