METHOD FOR SUPPRESSING ADHERING SUBSTANCE ON SEED CRYSTAL SURFACE IN PRODUCING METAL FLUORIDE SINGLE CRYSTAL BY MELT-SOLIDIFICATION METHOD USING SEED CRYSTAL

摘要

PROBLEM TO BE SOLVED: To provide a method for effectively suppressing adhesion of a black substance on the surface of a seed crystal in the production of a metal fluoride single crystal such as calcium fluoride by Czochralski method or Kyropoulos method.SOLUTION: In a period of at least from the start of melting a raw material metal fluoride until a seed crystal is brought into contact with the raw material melt, a portion (top end) of the seed crystal to be in contact with the raw material melt is kept in a standby mode in a high temperature region in a furnace so as to prevent condensation and adhesion of various kinds of volatile components on the top end of the seed crystal. Specifically, the top end is kept in a standby mode at a position c where the temperature is lower than the melting point of the raw material metal fluoride and equal to or higher than (melting point-400°C). When a scavenger is used, the seed crystal is started to be in a standby mode before the scavenger starts to melt and/or decompose.