Patent GB-1072765-A (GB)
Title: Process for the production of crystalline semiconductor bodies
IPC: H01L21/00
Filed: 1965-08-21
Abstract: 1,072,765. Semi-conductor devices. SIEMENS A.G. Aug. 24, 1965 [Aug. 25, 1964], No. 36211/65. Heading H1K. A process for producing a crystalline semiconductor body having layers of different resistivity comprises the steps of preparing a crystalline support of semi-conductor material by (a) depositing semi-conductor material from the gas phase on to a heated elongated filamentary carrier body made of the same semiconductor material by the thermal decomposition of a very pure compound of the material at the surface of the carrier body; (b) melting the body so obtained, if necessary after comminution; (c) mixing with the melt a doping substance in an amount such that the doped semiconductor material has a resistivity of less than 1 ohm-cm.; (d) drawing a crystal from the melt with the aid of a seed crystal; and (e) dividing the crystal so formed to form a plurality of supports; and depositing on the support one or more layers of semiconductor material having a higher resistivity. In a preferred embodiment a heated filament of monocrystalline or polycrystalline silicon is rotated about its longitudinal axis in a reaction vessel fed with a gaseous compound of silicon such as silicon tetrachloride, silico-chloroform or a silane. The thermal decomposition of the compound at the surface of the filament causes the carrier body to increase in thickness as the result of the deposition of very pure silicon. The carrier body is then placed in a crucible if necessary after comminution, and melted together with a doping material such as antimony or arsenic. Alternatively, the doping material may be added to the molten silicon. The amount of doping material is calculated so that the silicon support has a resistivity less than 1 ohm-cm., and preferably between 0.015 and 0.005 ohmcm. A monocrystal is drawn from the melt with the aid of a monocrystalline seed, and during this process fresh silicon and doping material are fed continuously to the crucible so that the volume of the melt and the level of doping are kept constant. The crystals are then cut into discs to form supports, and one or more layers of silicon doped to a resistivity of between 0.5 to 10 ohm-cm. are epitaxially deposited on the supports. Alternatively the layers may comprise a different semiconductor material which is similar to silicon as regards lattice structure and dimensions. The invention is also applicable to materials other than silicon, for example germanium. The Specification describes two methods of forming semi-conductor devices starting from supports manufactured as described above. In the first method, an N-type silicon support, or a P-type silicon support doped with gallium or boron, is heated in a reaction vessel fed with a gaseous compound of the semi-conductor material to be deposited, preferably a hydrogen halide compound mixed with a carrier gas such as hydrogen. The first layer to be deposited has the same type of conductivity as the support, and may be doped with phosphorous or boron. After deposition of the first layer the deposition process is sharply interrupted, e.g. by reducing the temperature, passing an inert gas instead of the gaseous compound, or displacing the reaction equilibrium by adding hydrogen chloride, and a second layer of opposite conductivity type is rapidly deposited. If a diode is to be produced, a further thick heavilydoped layer of the same conductivity type as the second layer is also deposited, whereas if a transistor is required a further layer of the same conductivity type as the support, but more lightly doped, is deposited on the second layer. Alternatively, a pellet of doping material may be alloyed into the second layer to produce a zone of opposite conductivity type. In the second method, a first layer of one conductivity type is deposited on a support of the same conductivity type and a zone of opposite conductivity type is produced in the layer e.g. by diffusing boron thereinto. A region of this zone is then doped to convert it to the first conductivity type, e.g. by alloying in a pill of antimony diluted with gold or by diffusing a doping substance into the region through a mask. This region constitutes the emitter of a transistor, the zone of opposite conductivity type forming the base and being provided with an aluminium ohmic contact. The. remaining parts of the layer may be etched away to form a mesa structure.