Improvements in or relating to processes and apparatus for the production of semi-conductor crystals

摘要

866,199. Semi-conductors. STE1VIENS & HALSKE A.G. Aug. 12, 1957 [Aug. 10, 1956], No. 25391/57. Class 37. A process for incorporating a doping substance into a semi-conductor melt comprises passing the substance in gaseous form from a storage vessel in which the substance is under pressure through a capillary nozzle into a stream of carrier gas consisting of hydrogen or of other gas inert to the doping substance and to the semi-conductor melt and wherein said substance is conducted together with said carrier gas to a treatment vessel in which the melt is located. The crystal 3 is heated in a reaction chamber to melt it. The doping substance may be BCl a and is contained in a storage vessel 6. The crystal may be of Si or Ge or of a compound of two or more different metals, the hydrogen can be replaced by a rare gas and any other boron halide such as the bromide BBr 3 can be used. The incorporation of the impurity or " doping " is to give the crystal a particular resistivity to increase the life of the charge carriers or to produce a crystal of a particular conductivity type, and the doping substance is generally distributed uniformly over the surface. In the particular process described the silicon crystal 3 is zone-melted, that is, successive zones of a vertically moving crystal are melted by a high-frequency coil 4. The proportions of carrier gas and "impurity gas" can be adjusted by the pressure in 6, by adjusting the size of the capillary nozzle, e.g. by a needle valve, and by adjusting the rate of flow of the hydrogen or other carrier gas. The final " doped " crystals have accurately-reproducible resistivities over a wide range, e.g. between 1 and 50 ohms/em. In a modification, crystal 3 can be melted in a crucible. In an example a silicon crystal with 10 atoms per cent of boron gives a resistivity of 10 ohms/cm. Prior art methods comprising the steps of conducting hydrogen or a rare gas over a heated liquid halide or mixing the carrier gas with halide gas and then reducing the proportion of the halide by freezing, are referred to.