Patent GB-1352449-A (GB)
Title: Semiconductor production
IPC: C30B27/02
Filed: 1971-07-27
Abstract: 1352449 Semi-conductor compounds SUMITOMO ELECTRIC INDUSTRIES Ltd 27 July 1971 [28 July 1970 29 July 1970 28 Aug 1970 28 Jan 1971 (2)] 35220/71 Heading C1A [Also in Divisions B1 and H1] In synthesis of a semi-conductor compound having at least one volatile component of low dissociation pressure; e.g. GaAs; (Fig. 2) a quartz crucible 19 is divided by a porous or perforated quartz or carbon wall 13 into low temperature and high temperature chambers; the latter containing GaAs polycrystal 11 covered with an inert substance 16, e.g. B 2 O 3  and former containing As at 12. The upper part of the crucible is surrounded by graphite vessel 20 and RF heater 21, while the lower part is surrounded by resistance heater 22; the whole being enclosed in an Ar or N 2  filled pressure vessel. The polycrystal and the inert overlay are melted and the As is heated to diffuse upwards through 13 into the melt, loss being prevented by the overlay 16 and the pressure atmosphere, and the composition of the melt being regulated by the temperature of the As. Stabilization occurs after a critical process time when a GaAs bead on pull rod 25 is dipped into the melt and slowly withdrawn to extract a single crystal 14. The basic material may be pure Ga or In and may be vapour doped with Te, Sn, Se, Zn, Cd, O, Cr or Fe. In a modification (Fig. 3, not shown) a graphite crucible is lined with BN and has a porous C or BN barrier between its high and low temperature chambers, and thermocouples control the temperatures thereof. A quartz inner crucible in the low temperature chamber contains red P and is protected from thermal radiation by a quartz wool plug. The lower end of the crucible is closed by a BN coated graphite screw plug; the threads allowing diffusion access for the pressure atmosphere. A Ga melt covered by inert material, e.g. B 2 O 3  is RF heated in the high temperature chamber and P is resistance heated in the low temperature chamber to diffuse P vapour into the melt; vapour pressure and variation of the melt from stoichometric proportions being temperature controlled. After stabilization, a single GaP seed is dipped into the melt and slowly withdrawn on a rotating puller rod to evolve a single GaP crystal. The melt may be doped with Te, Zn, Fe or O, and the crystal may similarly be grown from GaP polycrystal and P. GaAlAs may also be grown from GaAl solution and As; and ZnTe from ZnTe polycrystal and Zn. The porous wall may be of sintered boron nitride, or carbon fibre felt, and a lid may replace the closure screw. In a further modification (Fig. 4, not shown) a graphite crucible is used, coated on its inner surface with BN and divisible into two semicylindrical parts. It has an upper high temperature chamber containing a melt of polycrystal. line GaP under a B 2 O 3  layer separated from a low temperature chamber with a quartz inner vessel containing red P and closed with a graphite screw lid at the lower end admitting pressurized Ar gas through the screw threads. The chambers are separated by a porous wall and a quartz wool plug. After heating and stabilization a pedestal supporting the chamber is slowly lowered to evolve a self seeded GaP crystal. Pure Ga may be used as the melt. In a further modification (Fig. 5) a chamber 65 pressurized with Ar or N 2  contains RF heating coil 67 surrounding a graphite vessel 68 with resistance heaters 69, 70 and internally coated with BN at 71; a porous bottom wall 71 of cylindrical form having an axial hole and preventing the GaP polycrystal melt 85 covered with B 2 O 3  in the high temperature chamber 83 from flowing into the low temperature chamber 73, in which a quartz boat 74 contains red P; radiation shielded by quartz wool plug 76. A screwed graphite closure 77 admits pressure gas through the threads, and the vessel is supported by movable rods 79, 80. On heating P vapour diffuses into the melt and the rods are moved slowly to the left, so that a self seeded crystal 86 is accordingly grown. Pure Ga or mixed GaIn or InAl or GaAs may replace GaP in the high temperature chamber, with either P or As in the low temperature chamber for synthesis of GaAsP or InAlAs crystals. Process vessels may comprise (Fig. 6, not shown) an inner crucible of BN graphite or BN coated graphite containing a porous dividing wall, carried upon the high temperature chamber and screwedly seated on the low temperature chamber with an interviewing perforated alumina radiation shield; the chambers being of BN or BN coated graphite and the melt consisting of Ga overlain by B 2 O 3  with P in the low temperature chamber; or alternatively (Fig. 7, not shown) a unitary graphite or BN or BN coated graphite vessel with P in an inner crucible of the low temperature chamber and Ga overlain by B 2 O 3  in the high temperature chamber separated therefrom by a process wall and a perforated alumina radiation shield. The process is also applicable to synthesis of GaAlAs, GaInP, AlInP, ZnSeTe, ZnSiAsP, GaAlP, InP or GaAlP, composite crystals.