Patent GB-990161-A (GB)
Title: Semiconductor body
IPC: H01L29/04
Filed: 1961-03-29
Abstract: <PICT:0990161/C1/1> <PICT:0990161/C1/2> <PICT:0990161/C1/3> A monocrystalline polyhedral semi-conductor body has a polygonal cross-section and comprises a plurality of layers of monocrystalline material deposited on a seed crystal, adjacent layers having conductivities differing in type and/or degree separated by a transition region; the exterior surfaces of the layers form faces of polygonal prisms disposed about the longitudinal axis of the body, and transition region areas are substantially planar and parallel to the longitudinally extending crystal faces.  As shown, Fig. 1, seed crystals 14 comprising rods of monocrystalline Si, mounted in conductive chucks 15 and interconnected by a Si or C bridge 16, are heated in a closed reaction chamber 11 to c. 1250 DEG  C. by a source of electrical energy (not shown) connected to terminals 18; preferably, the crystals are pre-heated, e.g. by a source of radiant energy (not shown).  A carrier gas, preferably H2, is supplied to the chamber 11 from a source 24 for 1/2 -1 hour to clean the crystal surfaces; then SiHCl3 vapour from a source 26, and a vapour-source of active impurity from a source 28, are mixed with the H2 flow to the chamber.  The optimum temperature of the seed-crystals at this stage is 1170 DEG  C., and 240 g./hr. of SiHCl3 is entrained in 5.5 1./min. of total gas flow, producing a molar ratio of SiHCl3 : H2 of approximately 0.12 and resulting in c. 11 g./hr. of Si being deposited on the seed-crystals by virtue of the reaction: 3SiHCl3+H2-->2Si+SiCl4x5HCl.  The above molar ratio may vary within the range 0.015-0.30, preferably 0.06-0.20. Alternatively, the Si may be deposited by heatcracking a Si halide, e.g. SiCl4 or SiBr4, or from silane.  The impurity atom source, the type and amount of which in the gas-flow are determined by the desired type and degree of conductivity of the deposited layer, is a decomposable volatile compound of, e.g. B, Al, Ga; P, As, Sb, BCl3 and PCl3 are preferred sources of acceptor and donor impurities respectively. Deposition is continued until the deposited layer 4, Fig. 4, produces a polyhedral crystal of hexagonal cross-section. The longitudinally extending faces are oriented in the (III) plane, the sum of the Miller indices of the plane transverse to the longitudinal axis of the seed-crystal being arranged to be zero.  Other orientations result in different polygonal dispositions in the grown crystal.  The invention is applicable to growing monocrystals of Ge, SiC, and such III-V compounds as GaAs, InSb, GaP, also monocrystals comprising layers of different semi-conductor materials.  The geometry of the crystals varies with the material e.g. a Ge crystal (which may be formed by decomposing Ge halide vapour) is of quadrilateral cross-section, and some III-V compounds are triangular.ALSO:<PICT:0990161/C6-C7/1> A monocrystalline polyhedral semi-conductor body has a polygonal cross-section and comprises a plurality of layers of monocrystalline material deposited on a seed crystal, adjacent layers having conductivities differing in type and/or degree separated by a transition region; the exterior surfaces of the layers form faces of polygonal prisms disposed about the longitudinal axis of the body, and transition region areas are substantially planar and parallel to the longitudinally extending crystal faces.  As shown, Fig. 1, seed crystals 14 comprising rods of monocrystalline Si, mounted in conductive chucks 15 and interconnected by a Si or C bridge 16, are heated in a closed reaction chamber 11 to c. 1250  DEG C. by a source of electrical energy (not shown) connected to terminals 18; preferably, the crystals are preheated, e.g. by a source of radiant energy (not shown).  A carrier gas, preferably H2, is supplied to the chamber 11 from a source 24 for 1/2 -1 hour to clean the crystal surfaces; then SiHCl3 vapour from a source 26, and a vapour-source of active impurity from a source 28, are mixed with the H2 flow to the chamber. The optimum temperature of the seed-crystals at this stage is 1170  DEG C., when 240 g./hour of SiHCl3 is entrained in 5.51./minute of total gas flow, producing a molar ratio of SiHCl3:H2 of approximately 0.12 and resulting in c. 11 g./hour of Si being deposited on the seed-crystals by virtue of the reaction: 3SiHCl3+H2-->2Si+SiCl4+5HCl. The above molar ratio may vary within the range 0.015-0.30, preferably 0.06-0.20.  Alternatively the Si may be deposited by heat-cracking a Si halide, e.g. SiCl4 or SiBr4, or from silane.  The impurity atom source, the type and amount of which in the gas-flow are determined by the desired type and degree of conductivity of the deposited layer, is a decomposable volatile compound of, e.g., B, Al, Ga; P, As, Sb. BCl3 and PCl3 are preferred sources of acceptor and donor impurities respectively.  Deposition is continued until the deposited layer 41, Fig. 4, produces a polyhedral crystal of hexagonal cross-section.  The longitudinally extending faces are oriented in the (III) plane, the sum of the Miller indices of the plane transverse to the longitudinal axis of the seed-crystal being arranged to be zero.  Other orientations result in different polygonal dispositions in the grown crystal.  Additional layers, as 43, may be deposited, appropriate changes being made in the type and/or quantity of impurity atoms fed to the gas stream. Where a P-N junction 42 is formed between layers 41, 43, a longitudinal section, Fig. 5, of the crystal containing both layers may be diced to produce wafers to which leads and housings may be applied to form diodes.  In an example, a P+NN+Si body is formed by depositing Si from SiHCl3 under the conditions set out above on a Si seed-crystal of diameter 5 mm. for c. 8 hours to produce a 2 mm. thick layer having c. 1018 carriers/c.c. provided by the decomposition of BCl3, and a resistivity of c. 0.01 ohm-cm.  The chamber 11 is then flushed with a mixture of H2 gas, and SiCl4 from a source 30, while the crystal is kept at 1250  DEG C.; this removes excess B atoms; alternatively the crystals may be removed to a second reaction chamber.  The deposition of Si is then resumed, sufficient PCl3 to provide 1014 carriers/c.c. being introduced for about 30 minutes to produce a 0.006 inch thick layer of N-type Si.  The concentration of PCl3 is then increased to provide c. 1018 carriers/c.c. in the final layer.  When the reaction gas has been removed from the chamber the crystals are cooled at c. 100  DEG C./minute. Fig. 7a shows a PNIP transistor comprising a body diced from a longitudinal section of a crystal including four layers grown by the method of the invention.  The invention is applicable to growing monocrystals of Ge, SiC, and such III-V compounds as GaAs, InSb, GaP, also monocrystals comprising layers of different semi-conductor materials.  The geometry of the crystals varies with the material: e.g. a Ge crystal (which may be formed by decomposing Ge halide vapour) is of quadrilateral cross-section, and some III-V compounds are triangular.