Improvements in or relating to processes and apparatus for the production of ultra-pure substances

摘要

In the deposition of silicon from a silicon compound, e.g. silicon tetrachloride or trichlorosilane, on to an electrically-heated wire 4 of silicon, the wire 4 is heated by an electric current flowing substantially parallel to the longitudinal axis of the wire and the effect of gravity on the wire is at least partially counter-acted by interaction of the electric current and a magnetic field 5. The electric current and the magnetic field may be adjusted during the process to maintain to a desired extent the supporting force for the wire. Preferably the strength of the magnetic field is increased downwardly by using magnets, the pole faces of which are so shaped that the gap between them decreases in a downward direction (Fig. 2, not shown). The current through the wire may have direct and alternating components, the direct current being used for support of the wire and the alternating current for control of the heating. Alternatively two alternating currents of different frequency may be used with an alternating magnetic field of frequency corresponding to that of one of the currents. The production of single crystals may be facilitated by use of a current of frequency in the range 10-100 cycles/second to give a hammering effect on the wire. The ends of the wire and any mechanical supports therefor may be cooled.ALSO:In a modification of the process of the parent Specification, for producing pure semi-conductor material, the carrier body is heated by an electric current flowing substantially parallel to the longitudinal axis of the carrier body and the effect of gravity on the carrier body is at least partially cancelled by interaction of the electric current and the magnetic field. The electric current and the magnetic field may be adjusted during the process to maintain to a desired extent the supporting force for the carrier body. Preferably the strength of the magnetic field is increased downwardly by using magnets, the pole faces of which are so shaped that the gap between them decreases in a downward direction. The current through the carrier body may have direct and alternating components, the direct current being used for support of the body and the alternating current for control of the heating. Alternatively two alternating currents of different frequency may be used with an alternating magnetic field of frequency corresponding to that of one of the currents. The production of single crystals may be facilitated by use of current of frequency in the range 10-100 cycles/second to give a hammering effect on the carrier body. The ends of the body and any mechanical supports therefor may be cooled.