Method of making quartz glass crucibles, and apparatus carrying out the

Abstract

To make quartz glass crucibles suitable for drawing of single crystal silicon for electronic semiconductor applications, granular crystalline quartz or amorphous quartz glass is introduced into a rotating hollow mold which has gas-pervious wall regions at the side walls and bottom thereof, for example by having bores extending through a metal mold or being made of porous, sintered material. After introducing the raw material, a heat source, such as an electric arc, is introduced into the hollow mold, causing first sintering and then melting of an inner layer; upon introduction of the hollow mold, a vacuum is applied to the outside of the hollow mold, for example between the housing and the mold body, and, during continued rotation, to draw out any included gases and cause melting-together of vacuoles which, otherwise, might form due to included spaces and gases within the granular filling material. The vacuum is maintained during melting and rotation, heating being interrupted when a sufficienty thick inner wall of molten material has been formed, with an adjacent layer of sintered material leaving, however, granular material immediately adjacent the inner walls of the hollow mold to provide for heat insulation of the molten layer with respect to the hollow mold and protect the surface of the mold. The finished crucible can be ejected by introducing compressed air, rather than vacuum, to the outside of the hollow mold. Suitable vacuum is a pressure of less than 5,000 Pa, preferably less than 1,000 Pa.