Patent GB-990162-A (GB)
Title: Method of forming crystals of semiconductor material
Inventor: ALLEGRETTI JOHN EDWARD
IPC: H01L29/04
Filed: 1961-05-04
Abstract: In a method of forming a semi-conductor single crystal containing a plurality of layers each separated by a junction or transition region, a first layer of doped semi-conductor material is deposited from a vapour on to a heated semi-conductor crystal, the vapour containing decomposable compounds of semi-conductor material and of an active impurity, the crystal with the layer thereon is then disassociated from impurity atoms present in the chamber, and a second layer of semi-conductor material is then deposited upon the first layer <PICT:0990162/C1/1> <PICT:0990162/C1/2> <PICT:0990162/C1/3> from a vaporous decomposable compound of the semi-conductor material of the second layer. Silicon crystals 14, formed by cutting rods from a zone-refined crystal, or by crystal pulling, are etched and arranged in a reaction chamber 10, and are resistively heated to about 1250 DEG  C., possibly with the aid of radiant heating.  A source 24 of carrier gas, preferably hydrogen, is passed through the chamber to clean the crystals.  The temperature is then reduced to 1170 DEG  C. and a source 26 containing a decomposable compound of semi-conductor material preferably silicochloroform or other silanes (or halides of other materials), and a source 28 containing a decomposable compound of active impurity, preferably BCl3 or PCl3, are connected to the chamber. Silicon is deposited on the heated crystals by the reaction <FORM:0990162/C1/1> and atoms of boron or phosphorus are also deposited thereon.  A rate of flow of 240 grams of silicochloroform per hour in 330 litres of hydrogen per hour is preferred as it results in single crystal growth at a reasonable rate.  After depositing this layer sources 26, 28 are cut off from the chamber and impurity atoms deposited round the chamber are removed by flushing the system at 1250 DEG  C. for 15 to 60 minutes with silicon tetrachloride entrained in hydrogen.  Other suitable flushing gases include SiBr4, SiI4, HCl, Cl2, I2, Br2, and the effluent equilibrium gases from the first deposition step. After flushing, the system is purged with hydrogen for five minutes after which a second layer of semi-conductor material containing a second impurity, if desired, is deposited from the vapour as before. Thereafter the crystals are permitted to cool at 100 DEG  C. per minute in a flow of carrier gas. Specification 990,161 is referred to.ALSO:<PICT:0990162/C6-C7/1> <PICT:0990162/C6-C7/2> <PICT:0990162/C6-C7/3> In a method of forming a semi-conductor single crystal containing a plurality of layers each separated by a junction or transition region, a first layer of doped semi-conductor material is deposited from a vapour on to a heated semi-conductor crystal, the vapour containing decomposable compounds of semi-conductor material and of an active impurity, the crystal with the layer thereon is then disassociated from impurity atoms present in the chamber, and a second layer of semi-conductor material is then deposited upon the first layer from a vaporous decomposable compound of the semi-conductor material of the second layer. Silicon crystals 14, formed by cutting rods from a zone-refined crystal, or by crystal pulling, are etched and arranged in a reaction chamber 10, and are resistively heated to about 1250  DEG C., possibly with the aid of radiant heating.  A source 24 of carrier gas, preferably hydrogen, is passed through the chamber to clean the crystals.  The temperature is then reduced to 1170  DEG C. and a source 26 containing a decomposable compound of semi-conductor material preferably silicochloroform or other silanes (or halides of other materials), and a source 28 containing a decomposable compound of active impurity, preferably BCl3 or PCl3, are connected to the chamber.  Silicon is deposited on the heated crystals by the reaction <FORM:0990162/C6-C7/1> and atoms of boron or phosphorus are also deposited thereon.  A rate of flow of 240 grams of silicochloroform per hour in 330 litres of hydrogen per hour is preferred as it results in single crystal growth at a reasonable rate. After depositing this layer sources 26, 28 are cut off from the chamber and impurity atoms deposited round the chamber are removed by flushing the system at 1250  DEG C. for 15-60 minutes with silicon tetrachloride entrained in hydrogen.  Other suitable flushing gases include SiBr4, SiI4, HCl, Cl2, I2, Br2, and the effluent equilibrium gases from the first deposition step. After flushing, the system is purged with hydrogen for five minutes after which a second layer of semi-conductor material containing a second impurity, if desired, is deposited from the vapour as before. Thereafter the crystals are permitted to cool at 100  DEG C. per minute in a flow of carrier gas. A P+NN+ diode may be made using boron as the first impurity, sufficient to provide 1018 carriers per c.c. of silicon, and using phosphorus as the second impurity, initially using sufficient phosphorus to produce 1014 carriers per c.c., and then increasing the proportion to provide 1018 carriers per c.c.  The crystal faces may be arranged to lie in a particular crystallographic plane by suitable choice of axes of the starting crystal 14.  A hexagonal crystal, Fig. 4, having side faces in the (111) planes and end faces in the (<\>b211) plane may be sliced lingitudinally and the resulting strip cut transversely to form a number of diodes, Fig. 6, whose surfaces are then nickel plated and to which electrodes are attached using doped gold pellets as solder.  The construction of PNP and PNIP transistors is also described (Figs. 8 and 9, not shown) and a PNPNP structure is referred to.  Instead of silicon other semi-conductor materials including Ge, SiC, and AiiiBv compounds may be used, and successive layers may be of different semi-conductor materials. Specification 990,161 is referred to.