Method and apparatus for making a highly uniform low-stress single crystal by drawing from a melt and uses of said crystal

US7868708B2 · kind B2 · utility

Assignee

• Schott AG · DE

Inventors

• Gunther Wehrhan · Jena, DE
• Lutz Parthier · Kleinmachnow, DE
• Daniel Rytz · Herborn, DE
• Klaus Dupre · Idar-Oberstein, DE
• Lothar Ackermann · Idar-Oberstein, DE

Key dates

• Filing date: Dec 5, 2008
• Grant date: Jan 11, 2011
• Expiry date: Dec 5, 2028

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10T117/1004
• WIPO field: Surface technology, coating
• WIPO sector: Chemistry

Abstract

The method of making uniform low-stress crystals includes immersing a seed crystal held at a temperature under its melting point in a melt in a crucible and drawing it from the melt. The crystal and/or melt are rotated relative to each other and a planar phase boundary surface is maintained between them by detecting a surface temperature of the melt and/or crystal and controlling temperature fluctuations by increasing or decreasing the rotation speed. The single crystals obtained by this method have a diameter ≧50 mm and no visible growth strips in a fishtail pattern when a 2-mm thick sample is observed between crossed polarizers. These crystals have an index of refraction uniformity Δn of <1 ppm and a stress birefringence of <1 nm/cm at 193 nm, so that optical elements suitable for DUV lithography can be made from them.