Schott Ag

Hellma Materials Gmbh & Co. Kg

Schott Glas

Joerg Staeblein

Lutz Parthier

Gunther Wehrhan

Christian Kusch

Burkhard Speit

Jochen Alkemper

Martin Letz

Regina Martin

Klaus Petermann

Konrad Knapp

Andreas Weisleder

The method produces low-stress, large-volume crystals with low birefringence and uniform index of refraction. The method includes growing the crystal with larger than desired dimensions including diameter and height from a melt; cooling and tempering the crystal with the larger than desired dimensions and after the cooling and tempering removing edge regions of the crystal with the larger than desired dimensions so that a diameter reduction and a height reduction of at least five percent occurs respectively and so that the crystal has the desired dimensions of diameter and height. No further tempering takes place after removing of the edge regions.

Method for making low-stress large-volume crystals with reduced stress birefringence and more uniform refractive index and crystals made thereby

The method of making a single crystal, especially a CaFsingle crystal, includes tempering, in which the crystal is heated at &#x3c;18 K/h to a temperature of 1000&#xb0; C. to 1350&#xb0; C. and held at this temperature for at least 65 hours with maximum temperature differences within the crystal of &#x3c;0.2 K. Subsequently the crystal is cooled with a cooling rate of at maximum 0.5 K/h above a limiting temperature between 900&#xb0; C. to 600&#xb0; C. and then further below this limiting temperature at maximum 3 K/h. The obtained CaFcrystals have refractive index uniformity &#x3c;0.025&#xd7;10(RMS) in a (111)-, (100)- or (110)-direction and a stress birefringence of less than 2.5 nm/cm (PV) and/or a stress birefringence of less than 1 nm/cm (RMS) in the (100)- or (110)-direction. In the (111)-direction the stress birefringence is &#x3c;0.5 nm/cm (PV) and/or the stress birefringence is &#x3c;0.15 nm/cm (RMS).

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The optical elements for ultraviolet radiation, especially for microlithography, are made from cubic granet, cubic spinel, cubic perovskite and/or cubic M(II)- as well as M(IV)-oxides. The optical elements are made from suitable crystals of YAlO, LuAlO, CaAlSiO, KNaAlF, KNaScF, KLiAlFand/or NaAlLiF, (Mg, Zn)AlO, CaAlO, CaBOand/or LiAlO, BaZrOand/or CaCeO. A front lens used in immersion optics for microlithography at wavelengths under 200 nm is an example of a preferred optical element of the present invention.

Method for making optical elements for microlithography, the lens systems obtained by the method and their uses

A method is described for making an especially not-(111)-oriented low-stress large-volume crystal having a glide plane with reduced stress birefringence and more uniform refractive index. The method includes growing and tempering the crystal while heating and/or cooling to form a temperature gradient in order to relax stresses arising along the glide plane. During the tempering the heating and/or cooling occurs by heat transfer in a heat transfer direction and the heat transfer direction or temperature gradient is oriented at an angle of from 5&#xb0; to 90&#xb0; to the glide plane. Crystals with a uniform refractive index with variations of less than 0.025&#xd7;10(RMS value) are produced by the method.

Method for making low-stress large-volume not-(111)-oriented crystals with reduced stress birefringence and more uniform refractive index and crystals made thereby

The method for making a uniform, large-size single crystal of calcium fluoride includes placing a single precursor crystal of calcium fluoride in a tempering vessel provided with a cover; introducing calcium fluoride powder into the tempering vessel and subsequently heating the single precursor crystal, preferably in intimate contact with the calcium fluoride powder, in the tempering vessel together with the calcium fluoride powder for two or more hours at temperatures above 1150&deg; C. to temper the precursor crystal and thus form the uniform, large-scale single crystal of calcium fluoride. The uniform large-sized single crystals of calcium fluoride can be used to make improved lens, prism, light-conducting rod, optical window or other optical component for DUV photolithography, steppers, excimer lasers, wafers, computer chips and electronic devices containing the wafers and chips.

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Jena, Germany

Joerg Staeblein