Patent CA-2475212-A1 (CA)
Inventor: SCARLETE MIHAI V
IPC: H01L21/20
Filed: 2004-07-09
Abstract: 1. The invention provides a new process for the unidirectional growth of single crystal ingots of semiconductor materials such as silicon, germanium and silicon/germanium alloys, by coating the quartz crucibles holding the molten material. The coating process of quartz crucibles films aims at reducing chemical contamination of the single crystal, and/or enhance wetting properties of the crucible with respect to the contained molten materials. The ceramic coating may consist of silicon carbide, and/or silicon oxycarbide, silicon carbonitride, silicon carboronitride, or any other multilayered structure comprising at least one of these films. The unidirectional growth methods include Czochrralski (Cz), Magnetic Czochralski (MCz), Liquid Encapsulated Czochralski (LEC), Bridgman-Stockbarger, Vertical Gradient Freeze, Pedestal, Heat Exchange Method (HEM), Casting, Ribbon/Sheet Growth, etc. The synthesis of the coating include various methods, such as Chemical Vapour Deposition and related methods, polymer-derived methods, sputtering, Vapor Deposition Transport, laser ablation, etc.   2. The invention provides a new method for the confinement of the molten material during the unidirectional growth of semiconductor materials, by depositing a ceramic thin film on the inner and/or outer walls of the quartz crucible. The method of improving the quartz crucible holding the molten semiconductor material during a crystal growing process, consists of the deposition on the surface of the crucible of a film of silicon carbide, of silicon oxycarbide, or any multi layered structure coating comprising a film of the above mentioned materials at the interface with the molten silicon and/or at the interface with the holder/susceptor. The quartz crucible improved this way may be used for the Czochralski growth of single crystal, polycrystalline,or amorphous semiconductor silicon, germanium, or silicon /germanium alloys. The method results in: a) a reduced contamination with oxygen from SiO2 by reduced SiO formation at the SiO2/Si interface b) a reduced contamination with carbon via CO-dissolution from the gas phase, and c) a reduced contamination with SiC-particles produced the gaseous atmosphere are sought.      Since SiO, CO and SiC are responsible for the contamination of the semiconductor product with oxygen, carbon, and induce crystalline defects (stacking faults, dislocations, precipitates, resistivity instability via generation of thermal donors, etc), control of the formation of all these defects may be achieved via the use of the new crucible 3. The invention provides a new method for solid-source doping directly from the coated quartz crucible during the unidirectional growth of semiconductor materials, permitting control of the optimum delivery from/through the ceramic film of doping impurities such as B, Al, Ga, In, N, P, As, Sb, H that can be contained in the quartz wall or in the ceramic film. Also, incorporation of optimum concentrations of essential elements, such as oxygen and carbon, can be achieved below the saturation limit. Doping with S, Se, Te becomes also feasible in the case of silicon, germanium, silicon/germanium alloys and diamond-like semiconductor materials.   4. The invention provide an improved quartz crucible for the unidirectional growth of single crystal ingots of semiconductor silicon, germanium, and silicon/germanium alloys, characterized by reduced transfer of SiO and/or CO into the melt from the crucible/melt and/or the crucible/holder interface.  The crucible includes a body of vitreous silica having an inner surface which is in contact during the growth process with molten silicon, and an outer surface which is in contact with the graphite holder. The chemical reactivity of SiO2 (silica, quartz) produces SiO and CO at the two mentioned interfaces, species that are the main sources responsible for the contamination of the single crystal with oxygen and carbon the crucible unstable during. These two impurities are the main impurities in the semiconductor crystal, and the induced defects related to the presence of oxygen, carbon, and other species resulted from the chemical reactions involving these (such as in situ formation of SiC) in the single crystal include stacking faults, oxygen precipitates, formation of thermal donors, formation of dislocations, and others. Control over the production of these two species during the silicon melting and crystal growing process results implicitly in controlling the physical and chemical properties affected by the inclusion of these impurities in the crystal.   5. The invention provide a method of coating with silicon carbide/silicon oxycarbide films that can be used in applications where reduced chemical reactivity of SiO2 is sought, either for the protection of the silica material, or for to avoid contamination with silicon or oxygen from silica.     6. The invention provides s solid source of doping with oxygen consisting of an ultrathin silicon carbide/oxycarbide ceramic film deposited on a high purity quartz rod which is introduced in the molten zone during unidirectional solidification of the material. The ceramic ultrathin film acts as a barrier with controlled porosity against oxygen diffusion from the inner silica wall towards the semiconductor melt contained in the quartz crucible. 7. The invention provides a solid source for doping with elements from the series N,P,As,Bi,B,Al,Ga,In,S,Se,As,B,H, from thin silicon-based ceramic films deposited on quartz crucibles during unidirectional solidification of semiconductor materials.     The invention provide a new process for the unidirectional growth of single crystal ingots of semiconductor materials such as silicon, germanium and silicon/germanium alloys, by coating the quartz crucibles holding the molten material. The quartz crucibles are coated with ceramic films aims at reducing chemical contamination of the single crystal, and/or enhance wetting properties of the crucible with respect to the contained molten materials. The ceramic coating comprises silicon carbide, and/or silicon oxycarbide, silicon carbonitride, silicon carboronitride, or any other multilayered structure comprising at least one of these films.. The unidirectional growth methods include Czochrralski (Cz), Magnetic Czochralski (MCz), Vapor Controlled Czochralski (VCz), Liquid Encapsulated Czochralski (LEC), Bridgman-Stockbarger, Vertical Gradient Freeze, Pedestal, Heat Exchange Method (HEM), Casting, Ribbon/Sheet Growth, etc. The synthesis of the coating include various methods, such as Chemical Vapour Deposition and related methods, polymer-derived methods, sputtering, Vapor Deposition Transport, laser ablation, etc.  The invention provides a new method for the confinement of the molten material during the unidirectional growth of semiconductor materials, by depositing a ceramic thin film on the inner and outer walls of the quartz crucible.  The invention provides a new method for solid-source doping directly from the coated quartz crucible during the unidirectional growth of semiconductor materials, permitting control of the optimum delivery from/through the ceramic film of doping impurities such as B, Al, Ga, In, N, P, As, Sb, H that can be contained in the quartz wall or in the ceramic film. Also, incorporation of optimum concentrations of essential elements, such as oxygen and carbon, can be achieved below the saturation limit. Doping with S, Se, Te becomes also feasible in the case of silicon, germanium, silicon/germanium alloys and diamond-like semiconductor materials. The invention provide an improved quartz crucible for the unidirectional growth of single crystal ingots of semiconductor silicon, germanium, and silicon/germanium alloys, characterized by reduced transfer of SiO and/or CO into the melt from the crucible/melt and/or the crucible/holder interface.      The invention provide a method of coating with silicon carbide/silicon oxycarbide films that can be used in applications where reduced chemical reactivity of SiO2 is sought, either for the protection of the silica material, or for to avoid contamination with silicon or oxygen from silica.