Process for producing metal fluoride single crystal

Abstract

A metal fluoride single crystal pulling apparatus that upward pulling initiation through termination, in the state of shallow melt capable of highly effective inhibition of scatterer formation, can perform stable growth of single crystal and can suppress any mixing of air bubbles and occurrence of crystal break during crystal growth, etc; and a process for producing a metal fluoride single crystal therewith. As a crucible for accommodating a melt of raw metal fluoride, use is made of a double structured crucible composed of an outer crucible and an inner crucible. In the upward pulling of single crystal, the accommodation depth of inner crucible relative to the outer crucible is increased in accordance with any decrease of melt accommodated in the inner crucible according to the growth of single crystal, so that the melt accommodated in the outer crucible is fed into the inner crucible to thereby maintain the amount of melt accommodated in the inner crucible within a given range. Further, at the position of an opening that upward opens any gap space between an external surface of outer crucible and an internal surface of inner crucible, or an interstice, situated below the opening, between a side wall internal surface of outer crucible and a side wall external surface of inner crucible, there is disposed a cutoff member that cuts off at least part of the position.