Patent GB-997997-A (GB)
Title: Epitaxial growth and doping from a gaseous source
IPC: H01L21/00
Filed: 1963-01-23
Abstract: <PICT:0997997/C1/1> A mono-crystalline semi-conductor material is coated with an epitaxial deposit of the same material, and simultaneously is coated with a controlled amount of a doping material, by heating the semi-conductor substrate in a stream of a carrier gas into which is injected (1) a gaseous compound of the semi-conductor material, and (2) a mixture of diluent gas and a gaseous hydride consisting of the doping material pre-diluted with diluent gas. The two independent steps of diluting the gaseous hydride with controlled amounts of diluent gas provides an accurate control over the amount deposited.  The doping compound is preferably phosphine, diborane, or arsine, but hydrides of Al, Ga, Zn, and Sb are also referred to.  The carrier and diluent gas is hydrogen. The doping level is controlled to a selected value, and this may be varied during deposition giving layers of different doping concentration.  Semi-conductor materials are Si or Ge, and gaseous compounds of these used for coating are halides. Fig. 3 shows wafers 21 of a semi-conductor heated in an enclosure 27 through which hydrogen flows from a source 43.  SiCl4 vapour is generated in a saturator 31 fed with hydrogen from a source 32, and then passes through a control valve 39 to the chamber 27.  The substrate is maintained at 1000 DEG  to 1300 DEG  C. for silicon, and at 700-850 DEG  C. for germanium.  The hydride doping compound, e.g. PH3 admixed with hydrogen, is supplied from a source 51, and diborane/hydrogen mixture from 52.  Additional controlled amounts of hydrogen is supplied from 67, 68, each supply being individually controlled by valves, and the final diluted mixture being also controlled at 56, 57 before admission to the main stream of hydrogen and semi-conductor material at 60.ALSO:Epitaxial deposition of monocrystalline semiconductor material on a substrate crystal of said semi-conductor material and simultaneously depositing a controlled amount of a doping material, is achieved by heating the substrate crystal in a reaction enclosure and passing therethrough a main stream of a carrier gas having injected into said main stream (i) a gaseous compound of the semi-conductor material from which elemental semi-conductor material deposits on said crystal element, and (ii) a gaseous mixture of a diluent gas into which has been mixed a hydride compound of a doping impurity supplied from a gaseous source of gaseous hydride compound already mixed with said diluent gas.  The two independent diluting steps of the doping hydride compound, provides an accurate control of the quantity deposited. The hydride compound of <PICT:0997997/C6-C7/1> the doping element is preferably phosphine diborane and arsine, but hydrides of Al, Ga, In, and Sb are also referred to.  The carrier gas is preferably hydrogen, which gas is also the diluent in a hydride-hydrogen mixture.  The invention allows for the doping level of the resulting epitaxial film to be controlled at a selected value, which may be varied during deposition giving layers of different doping concentration.  The semi-conductor material is either silicon or germanium.  Gaseous compounds of semi-conductor material used may be silicon tetrachloride, germanium tetrachloride and trichlorisilane; other halides and hydrogen-halides of Si and Ge may be used. Fig. 3 shows wafers 21 of semi-conductor material heated in enclosure 27 through which hydrogen carrier gas streams from a source 43.  Vapours of SiCl4 are obtained from saturator 31 which contains said compound in liquid form, and through which liquid hydrogen is circulated from source 32 and then passes through a control valve 39 to the chamber 27.  For silicon substrates the reaction temperature is maintained from 1000  DEG C. to 1300  DEG C., preferably 1130-1200  DEG C.; for germanium the temperature range is 700-850  DEG C., preferably 750-800  DEG C.  The doping hydride compound, e.g. phosphine diluted with hydrogen supplied from source 51 and diborane and hydrogen supplied from source 52, are supplied from steel welding cylinders preferably with 102-104 gaseous hydride per 106 parts hydrogen.  Additional controlled amounts of carrier gas are added from 67, 68, each supply being individually controlled by valves, and the diluted mixture being also controlled at 56, 57 before admission to the main stream of hydrogen and semi-conductor material at 60.