METHOD FOR MANUFACTURING LARGE-VOLUME CaF2 SINGLE CRYSTAL FOR OPTICAL ELEMENT WITH OPTICAL AXIS PARALLEL TO (100)-CRYSTAL AXIS OR (110)-CRYSTAL AXIS, AND CaF2 SINGLE CRYSTAL MANUFACTURED BY THE METHOD

摘要

PROBLEM TO BE SOLVED: To provide a method for tempering to obtain a single crystal having excellent optical characteristics such as refractive index uniformity or stress birefringence in a (100) or (110) direction of the single crystal and free from stress in the manufacture of a calcium fluoride single crystal to be used for microlithography at short wavelength of 250 nm, preferably 193 nm, and to provide a calcium fluoride crystal and an integrated circuit and an electronic device using the above crystal.;SOLUTION: The method includes, for the purpose of tempering a crystal, steps of: (a) heating the crystal to 1,000C to 1,350C at less than 18 K/h heating rate; (b) holding the crystal at the heating temperature of the step (a) for at least 65 hours to control the temperature difference in the crystal to maximum 0.2K; (c) cooling the crystal to a temperature range above a limiting temperature between 900C and 600C at maximum 0.5 K/h cooling rate; and (d) cooling the crystal at maximum 3 K/h cooling rate to a temperature further below the above temperature range.;COPYRIGHT: (C)2005,JPO&NCIPI