Patent GB-775986-A (GB)
Title: Improvements in or relating to processes and apparatus for treating semi-conductor devices
IPC: C30B15/02
Filed: 1954-02-15
Abstract: <PICT:0775986/III/1> A longitudinally extending semi-conducting device or assembly of silicon is treated by a zone-melting operation, the material being liquified only in a limited zone which moves along the materal and the molten material in the zone is supported otherwise than by means of a supporting crucible or the like. Support for the molten material may be provided by an electrical field counteracting the effect of gravity on the molten material, by a ring of nozzles which blow a protective gas on to the molten zone from below to prevent the molten material from dropping or, where the device is positioned at an inclination or horizontally, by arranging that the molten zone is confined to the upper part only, the lower part being maintained solid, e.g. by blowing a cool protective gas against the lower part.  In the latter method the device is rotated about its axis so that the molten zone pursues a spiral path along the device.  The ends of the device may be fastened in supports which can be oscillated or rotated.  Where the supports are rotated the speed of rotation is arranged to be above or below the molten zone and may be so high that undissolved foreign substances are conveyed by centrifugal action to the outer surface from which they are later removed.  Alternatively the supports may be rotated in opposite directions.  Material may be added to the molten zone e.g. donors and acceptors, at suitable points along the device or they may be introduced as constituents, at appropriate points along a sintered body to be treated.  The ends of the device may be moved towards or away from each other during treatment to modify the cross-section of the device.  The heating means may comprise one or more incandescent rings arranged symmetrically with respect to the axis of the device and optical means such as a concave mirror may be used to concentrate the heat on one or more narrow surface zones of the device. Preheating, e.g. capacitative, resistance or radiation, may be employed.  As shown in the Figure the upper end 111 of a rod being treated is clamped in a holder 199 and can be rotated by means of an electric motor, situated below the base plate 115, operating through a gear 167.  The lower end of the rod is also rotatably mounted in a holder 114.  The upper end of the rod can be moved longitudinally with respect to the lower end by arm 129 of an internally threaded support 118 which is moved by rotation of a threaded rod 116.  The heating means consists of a tungsten plate 122 bent to form a ring and similarly mounted to be moved in a vertical direction by rotation of a threaded rod 117.  Guide means 121 and 124 for the lower and upper parts respectively of the device are provided.  Current is supplied to the heating ring by flexible cables attached to terminals on the base plate and to terminals on the support for the heater ring.  The apparatus, except for the driving motors, is mounted within a cover 131 clamped in an air-tight manner to the base plate, the cover being surrounded by a cooling coil 132.