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

US7476274B2 · 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: Sep 11, 2006
• Grant date: Jan 13, 2009
• Expiry date: Sep 11, 2026

Classification

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

Abstract

The method provides a uniform low-stress single crystal in a predetermined crystal orientation. The method of making it includes immersing a single crystal held at a temperature under its melting point in a melt of crystal raw material and drawing it from the melt to grow the crystal. The crystal and/or melt are rotated relative to each other during the crystal growth. A planar phase boundary surface is maintained by detecting at least one characteristic surface temperature in an interior of a crucible containing the melt and controlling temperature fluctuations by increasing or decreasing the rotation speed when they occur. The single crystals obtained by this method have a diameter of at least 50 mm and no visible growth strips in a fishtail pattern when a 2-mm thick sample is observed between crossed polarizers. Optical elements suitable for DUV lithography can be made from these crystals.