Patent GB-784617-A (GB)
Title: Improvements in or relating to processes and apparatus for drawing fused bodies
IPC: C30B15/02
Filed: 1955-02-23
Abstract: <PICT:0784617/III/1> <PICT:0784617/III/2> In a process for drawing a fused rod-shaped crystalline body of predetermined volume from a melt in a crucible, fresh material is supplied to the melt in the crucible during the withdrawal of the fused body in such a way that the quantity of the melt is kept smaller than the predetermined volume. In one embodiment of the invention (Fig. 1), a melt of semi-conductor material, such as germanium, silicon, indium antimonide, or aluminium antimonide, is contained in a crucible 11, which may be made of graphite, magnesium oxide or aluminium oxide, and is supported by a holder 20 clamped to guide pins 24.  The holder 20 may be a resistance element which may be heated to preheat the crucible 11. Crucible 11 is surrounded by an annular heating member 17, which may be a resistance element or an inductively acting heating coil, and which is supported by guide-pins 24 in such manner that it may be moved upwards or downwards by a spindle 23.  A mono-crystalline nucleus is clamped in a lower holder 13 and is in contact with a molten bead of material descending from an opening in the bottom of crucible 11, and the holder 13 is gradually lowered so that a mono-crystalline rod 12 is formed.  Meanwhile a sintered rod 14 of supply material clamped in an upper holder 15 is gradually fed into the crucible 11.  The whole is contained under a hood 33 on a base 30, the process being carried out in a vacuum or in an inert gas. Rods 12 and 14 may be rotated.  Alternatively, the supply rod 14 may remain stationary while the crucible 11 and rod 12 are lowered, or the crucible 11 and-at a lower speed-the supply rod 14 are moved upwards, while the rod 12 is held stationary or lowered.  Additives to produce P-N- or N-P-junctions, or a succession of such junctions, may be added to the crucible 11 from chambers in a cylinder 50, which, when rotated, causes pellets of material to fall through a hole in a plate 48 down a tube 55.  The amount of melt in the crucible 11 is smaller than one-tenth of the rod 12 which is finally formed.  In another embodiment (Fig. 6), the apparatus is enclosed in a quartz tube 60 which is sealed in vacuum-tight fashion by seals 57 and 58, the crucible 11 being heated by an induction coil 64 which also supports the crucible, and the supply material is fed to the crucible in the form of powder from a container 70 having a narrow outlet aperture which may be closed by a plug 69 on a rod 71.  The rod 12 of fused material is withdrawn downwardly as before by a holder 13. Additives may be introduced in the crucible through a tube 76 from an arrangement similar to that described above, which is provided at the lower end of the container 70.  Several modifications of the crucible design are described in which the outlet aperture of the crucible is variable by means of a needle adjustable in the axial direction; the crucible is rotated about the axis of its outlet aperture; the outlet aperture is in the side wall of the crucible so that the fused rod is withdrawn in the horizontal direction; and the crucible has the form of a U-shaped tube, the fused rod being withdrawn upwardly from an outlet aperture in one arm which is at a level lower than the level of the melt in the other arm, where the supply material is fed to the crucible.  In a further embodiment the apparatus is similar to that shown in Fig. 1, but the rod of supply material may be removed from the crucible and replaced by an auxiliary rod which is then withdrawn upwardly carrying with it liquid contained in the crucible, so that an additive of one type may be used, the melt in the crucible removed an replaced by melt with an additive of another type incorporated, and so on to give a fused rod having a succession of zones of different types of conduction and/or different degrees of conductivity.