Abstract: An argon recovery and purification process in which the consumption of energy is small because of simple steps, is provided. This process comprises: a first step of reacting impure argon gas with hydrogen gas (H2) so that oxygen (O2) contained in the impure argon gas is converted to water (H2O), thereby substantially removing oxygen (O2) from the impure argon gas; a second step of introducing the impure argon gas into an adsorption unit for adsorbing water (H2O) and carbon dioxide (CO2) contained in the impure argon gas, thereby substantially removing the water (H2O) and carbon dioxide (CO2) from the impure argon gas; and a third step of subjecting the impure argon gas to a low temperature liquefaction and introducing the liquefied argon into a rectification unit for removing low boiling point impurity components and high boiling point impurity components contained in the impure argon gas by purification and separation, thereby obtaining substantially pure argon gas.

Abstract: Catalytic dehalogenation (or hydrodehalogenation) of halogen-containing compounds of elements of group IV of the periodic table in the presence of hydrogen is carried out using a finely-dispersed catalytically active material which comprises silicon and at least one transition metal, and which is characterized by high catalytic activity and stability. This process can be used, for example, for synthesizing compounds or alternatively for decomposing halogen-containing compounds, for instance in waste-water or waste-gas purification processes. It is also suitable for dehalogenation (hydrodehalogenation) of halogen-containing silane compounds, for instance of silicon tetrachloride or alkyl trichlorosilane compounds, and the original purity of the silanes used as starting materials is retained by the products. Tetrachlorosilane, for example, can be converted into trichlorosilane.

Abstract: An improved reactor for a high-temperature deposition reaction on seed particles is constructed with a fluidized bed which is divided into a heating zone and a reaction zone by a partition. Seed particles in the heating zone are fluidized by a carrier gas and are heated by microwaves. On the other hand, the reaction zone for the deposition reaction, through which reaction gases pass, is heated by particle mixing between the reaction zone and the upper section of the heating zone. Subsequently, a desired reaction temperature at the reaction zone is maintained stable without deteriorating the microwave heating of the heating zone.

Abstract: The present invention is a method for controlling the carbon balance of a silicon smelting furnace. The inventors lave discovered that when the concentration of calcium within the silicon formed in the furnace is maintained within a range of about 0.4 to 2.0 weight percent, the calcium yield of the furnace is a rapid and sensitive indicator of the carbon balance of the furnace. More specifically, the inventors have found that a calcium yield of less than about 80 weight percent indicates a negative carbon balance in the furnace, a calcium yield of greater than about 90 weight percent indicates an excess carbon balance in the furnace, and a calcium yield within a range of about 80 weight percent to 90 weight percent indicates a furnace in carbon balance. In a preferred embodiment of the present invention, calcium yield is used in conjunction with a harmonic volts parameter and a electrode consumption measurement to control carbon balance of the furnace.

Abstract: An improved method is provided for the deposition of high-purity silicon on silicon particles from silicon source gases in a fluidized bed reactor which is divided into a heating zone and a reaction zone by a partition. Silicon particles in the heating zone are fluidized by a carrier gas such as hydrogen and are heated by microwaves. On the other hand, the reaction zone for the deposition of silicon, through which reaction gases including the silicon source pass, is heated by particle mixing between the reaction zone and the upper section of the heating zone. Subsequently, a desired reaction temperature at the reaction zone is maintained stable without deteriorating the microwave heating of the heating zone.

Abstract: A carbide former is introduced into briquettes in the production of silicon in an electric-arc low-shaft furnace to improve the trapping of silicon oxide rising in the furnace and increase the silicon yield. The carbide former can be calcium, magnesium or aluminum, preferably in the form of the silicate and most advantageous is magnesium silicate.

Abstract: A furnace for the production of silicon metal or a silicon containing alloy includes a charge feed tube for supplying a silicon containing charge to a reaction zone. Silicon monoxide gas generated in the reaction zone is allowed to rise through the tube and is combined with natural gas that has been introduced into the top of the tube. The natural gas and the silicon monoxide combine to form silicon carbide which is carried back into the furnace with the charge.

Abstract: The present invention is a process for the carbothermic reduction of silicon dioxide to form elemental silicon. Carbon balance of the process is assessed by measuring the amount of carbon monoxide evolved in offgas exiting the furnace. A ratio of the amount of carbon monoxide evolved and the amount of silicon dioxide added to the furnace is determined. Based on this ratio, the carbon balance of the furnace can be determined and carbon feed can be adjusted to maintain the furnace in carbon balance.

Abstract: The present invention relates to an insulation system for a high temperature reactor in which chlorosilanes and hydrogen gases are present. The system described comprises an inner graphite radiant heat shield and an outer carbon-based, rigid, felt insulation of high density. The inner radient heat shield provides increased chemical stability at the hot face in a chlorosilane and hydrogen reactor. Also, the inner radient heat shield reduces the temperature at the interface with the carbon-based rigid felt, thereby reducing the reactivity of the chlorosilanes with the carbon-based rigid felt. The high density of the carbon-based rigid belt further reduces radiant heat loss. More importantly, the high density of the carbon-based rigid felt excludes the highly heat conductive hydrogen gas from the voids of the flet. The insulation system, as described, allows reactors containing chlorosilanes and hydrogen gases to be operated at higher and more efficient temperatures for longer periods of time.

Abstract: A method and apparatus for producing or manufacturing a high purity metallic silicon takes a process for generating silicon monoxide by causing reaction between a silicon dioxide containing material and molten state metallic silicon. The silicon monoxide thus generated is sucked for reduction by means of a reducing agent including a carbon containing material and a silicon containing material.

Abstract: A method of manufacturing high-purity silicon crystals, which comprises depositing silicon on the surface of high-purity silicon particles, while feeding into a fluidized bed reactor at a high temperature a material gas consisting of high purity chlorosilane and a diluting gas, said method having a silicon deposition rate in excess of about 0.4 .mu.m/min.

Abstract: A method for growing silicon single crystal uses as materials, silicon granules prepared by the silane process and having a residual hydrogen concentration of 7.5 wtppm or less, silicon granules prepared by the trichlorosilane process and having a residual chlorine concentration of 15 wtppm or less. In the case where such silicon granules are used, a bursting phenomenon does not occur when the silicon granules are melted. As a result, there is no scattered matter due to the bursting phenomenon, whereby the growth condition of the single crystal is not disturbed.

Abstract: Vaporized silicon halide is mixed with a vaporized alkali metala in a reactor chamber in an exothermic reaction producing liquid silicon droplets and gaseous alkali metal halide, and then passed out of the reactor chamber through a nozzle in a supersonic jet. The supersonic jet is produced by utilizing vacuum means to maintain the exit chamber at a lower pressure than the reactor chamber. Separation of the silicon from the salt by-products is performed by shock wave impaction separation technique wherein the products of the complete reaction between the alkali metal and silicon halide are made to impinge upon an unrestricted, flat surface so that the direction of flow of the gas changes abruptly and a shock zone is created above the flat surface. The silicon droplets are carried by their large forward momentum through the shock zone onto the separating surface where they are deposited. The gaseous alkali metal halide flows across the surface and is thus separated from the silicon product.

Abstract: The instant invention is a process for preparing silicon metal in a direct current, submerged-arc furnace. The process comprises adding a source of silicon dioxide and a source of carbon to a substantially closed furnace. Heat is provided to the furnace by striking a direct current arc between a moveable cathode and a anode functional hearth. Silicon metal is tapped from the furnace. The described process may also be used to prepare silicon metal alloys.

Abstract: A method of producing submicron nonagglomerated particles in a single stage reactor includes introducing a reactant or mixture of reactants at one end while varying the temperature along the reactor to initiate reactions at a low rate. As homogeneously small numbers of seed particles generated in the initial section of the reactor progress through the reactor, the reaction is gradually accelerated through programmed increases in temperature along the length of the reactor to promote particle growth by chemical vapor deposition while minimizing agglomerate formation by maintaining a sufficiently low number concentration of particles in the reactor such that coagulation is inhibited within the residence time of particles in the reactor. The maximum temperature and minimum residence time is defined by a combination of temperature and residence time that is necessary to bring the reaction to completion.

Abstract: What is described is a process for the production of silicon via the carbothermic reduction of silicon dioxide in which silicon carbide is fed as the total reductant source or as a portion of the reductant input. The process also includes recovery and recycle to the furnace silicon monoxide and other silicon-containing materials from the by-produced gases from the furnace to maximize raw material efficiency. Finally, the process includes the recovery of value from the by-produced gases via the use of the gases as a chemical intermediate or the use of the gases as a fuel for a combustion process.

Abstract: The process for producing silicon suitable for use in solar cells is improved by reacting a gaseous silicon compound with aluminum wherein a finely dispersed molten surface of pure aluminum or an aluminum/silicon alloy is intensively contacted with the gaseous silicon compound during the reaction.

Abstract: An improved process for purifying and refining silicon containing impurities comprises:(i) continuously melting impure silicon to form a thin film silicon melt, preferably on an inclined surface of a silicon-resistant material,(ii) continuously treating the thin film silicon melt with a reactive gas with or without an inert gas,(iii) optionally degassing the treated silicon melt, and thereafter(iv) continuously crystallizing the treated silicon.

Abstract: A method for producing metal by the reduction of a metal halide by a reducing metal agent capable of continuously producing homogeneous metal of high purity. In the method, particles of the same metal as the metal to be produced are charged into a reaction vessel and the metal halide and the reducing metal agent both in vapor form, are ejected upwards into the reaction vessel from its lower portion to form a fluidized bed of the metal particles in the vessel. The reducing reaction between the two vapors takes place on the surface of the metal particles at a temperature below the melting point of the metal product and at a pressure below a vapor pressure of each of the reducing metal agent and the metal halide at that temperature, resulting in depositing and growing the metal product on the surface of the particles.

Abstract: Hydrogen-containing effluent gas can be treated with activated carbon to remove boron or phosphorus impurity prior to recycle to a fluidized bed reactor. The process is conducted at cryogenic temperatures.

Abstract: Undesirable conversion of a silicon source, such as silane, in the freeboard above a fluidized bed of silicon particles in a fluidized bed reactor, can be reduced by cooling the gas within the freeboard. Preferably, the reduction in temperature is achieved by introducing into the freeboard, a stream of relatively cool quench gas such as hydrogen, which also reduces the concentration of silane in the freeboard. As a result of these two factors, the invention improves the service factor of the fluidized bed apparatus, and reduces the amount of silane conversion to undesired by-products.

Abstract: A smelting process for making elemental silicon and alloys thereof is disclosed. The smelting process is of the electrometallurgical type for producing elemental silicon from silicon dioxide including silicon alloyed and silicon in a substantially pure form. The process includes establishing and maintaining countercurrent contact between collected oxide and a bed of carbonaceous reductant for reducing at least part of the collected oxide to additional elemental silicon.

Abstract: Shaped articles, e.g., bars, of semiconductor-grade, ultra-pure silicon, are facilely and efficiently produced by thermally decomposing/pyrolyzing a monosilane feedstream on a red-heated silicon support member, whereby high purity silicon is deposited thereon, and thence recycling the majority of the by-product reaction admixture into said monosilane feedstream.

Abstract: A process is disclosed for producing a solid material which, in some cases, may have a resultant purity of 99.999% or better which comprises contacting the solid material at a temperature approaching the melting point of the solid material with a purifying agent which is substantially nonreactive with the solid material to cause the impurities in the solid material to enter the material. After cooling, the purified solid material may be separated from the purifying agent and the impurities therein by leaching.

Abstract: A process for the production of silicon in a low-shaft electric furnace, in which raw-material blanks are first formed which contain fine-grain silicon dioxide, e.g. in the form of sand, and carbon in excess in respect of the reduction to silicon carbide and the raw-material blanks are introduced into the low-shaft furnance as a charge in mixture with silicon dioxide in lump form. The silicon dioxide in the raw-material moldings is reduced to silicon carbide in an upper part of the low-shaft electric furnace at a temperature of below 1600.degree. C. and coke structure agglomerates are formed from the excess carbon of the raw-material moldings. In a lower part of the low-shaft electric furnace, the silicon dioxide in lump form, is reduced to silicon with silicon carbide and carbon from the coke structure agglomerates at a temperature of above 1600.degree. C., preferably from 1800.degree. to 200.degree. C. The raw-material moldings are formed with bituminous binder containing a fine-particle silica powder.

Abstract: An apparatus for maintaining the purity of solid/granular product and dispensing high purity granular product from a vessel. A noncontaminating surface is provided by a cup, cylinder, or other structure having a surface of silicon, silicon carbide, silicon nitride, sialon, or similar materials and preferably operates as an angle of repose valve in a pressurized system to prevent contamination by undue contact of the high purity product with conventional gastight valves such as ball valves, butterfly valves, pinch valves, etc.

Abstract: What is described is an improvement to a process for the preparation of silicon from the reduction of silicon dioxide with a solid carbonaceous reducing agent, the improvement comprising feeding calcium compounds into the reaction zone of a silicon furnace, and controlling and maintaining a desired calcium level in the reaction zone of the silicon furnace. The calcium compounds may be fed to the silicon furnace as a constituent of either the silicon dioxide or solid carbonaceous reducing agent feeds, as a separate feed, or as a combination of two or more of these feeds.Also described is an improvement to a process for the preparation of silicon carbide from the reduction of silicon dioxide with a solid carbonaceous reducing agent.

Abstract: Apparatus for producing low cost, high purity solar grade Si wherein a reduction reaction, preferably the reduction of SiF.sub.4, by an alkali metal (Na preferred) is carried out by jetting a spray of reactants into a reaction chamber at a rate and temperature which causes the reaction to take place far enough away from the entry region to avoid plugging of reactants at the entry region and wherein separation in the melt is carried out continuously from the reaction and the Si can be cast directly from the melt. The melt separation is provided by openings in the reaction chamber wall between about 2 to about 3.5 millimeters in width. The Si is retained within the reaction chamber due to its surface tension.

Abstract: The invention relates to a method for preparing polycrystalline pure silicon by reducing gaseous silicon tetrafluoride at a raised temperature by means of alkali metal or alkali earth and by recovering the silicon by means of liquid phase separation. According to the invention, the gaseous silicon tetrafluoride is reduced by fused alkali metal or alkali earth or powder dispersed into a liquid intermediate agent boiling at a high temperature.

Abstract: Process and apparatus for producing low cost, high purity solar grade silicon ingots in single crystal or quasi single crystal ingot form in a substantially continuous operation in a two stage reactor starting with sodium fluosilicate and a metal more electropositive than silicon (preferably sodium) in separate compartments having easy vapor transport therebetween and thermally decomposing the sodium fluosilicate to cause formation of substantially pure silicon and a metal fluoride which may be continuously separated in the melt and silicon may be directly and continuously cast from the melt.

Abstract: A reactor apparatus (10) adapted for continuously producing molten, solar grade purity elemental silicon by thermal reaction of a suitable precursor gas, such as silane (SiH.sub.4), is disclosed. The reactor apparatus (10) includes an elongated reactor body (32) having graphite or carbon walls which are heated to a temperature exceeding the melting temperature of silicon. The precursor gas enters the reactor body (32) through an efficiently cooled inlet tube assembly (22) and a relatively thin carbon or graphite septum (44). The septum (44), being in contact on one side with the cooled inlet (22) and the heated interior of the reactor (32) on the other side, provides a sharp temperature gradient for the precursor gas entering the reactor (32) and renders the operation of the inlet tube assembly (22) substantially free of clogging. The precursor gas flows in the reactor (32) in a substantially smooth, substantially axial manner.

Abstract: Process for producing low cost, high purity solar grade Si wherein a reduction reaction, preferably the reduction of SiF.sub.4, by an alkali metal (Na preferred) is carried out inside a reaction chamber. The chamber wall and bottom surfaces are configured so as to facilitate the continuous separation of the products of reaction (Si and NaF) and removal of the molten salt by discharging the salt through one or more ports at the bottom of the reaction chamber. Such process is especially useful where it is desirable to discharge the reaction salt products from the reactor and retain silicon within the chamber for later removal.

Abstract: Undesirable conversion of a silicon source, such as silane, in the freeboard above a fluidized bed of silicon particles in a fluidized bed reactor, can be reduced by cooling the gas within the freeboard. Preferably, the reduction in temperature is achieved by introducing into the freeboard, a stream of relatively cool quench gas such as hydrogen, which also reduces the concentration of silane in the freeboard. As a result of these two factors, the invention improves the service factor of the fluidized bed apparatus, and reduces the amount of silane conversion to undesired by-products.

Abstract: A reactor apparatus (10) adapted for continuously producing molten, solar grade purity elemental silicon by thermal reaction of a suitable precursor gas, such as silane (SiH.sub.4), is disclosed. The reactor apparatus (10) includes an elongated reactor body (32) having graphite or carbon walls which are heated to a temperature exceeding the melting temperature of silicon. The precursor gas enters the reactor body (32) through an efficiently cooled inlet tube assembly (22) and a relatively thin carbon or graphite septum (44). The septum (44), being in contact on one side with the cooled inlet (22) and the heated interior of the reactor (32) on the other side, provides a sharp temperature gradient for the precursor gas entering the reactor (32) and renders the operation of the inlet tube assembly (22) substantially free of clogging. The precursor gas flows in the reactor (32) in a substantially smooth, substantially axial manner.

Abstract: What is disclosed is an improvement in a process for the carbothermic reduction of silicon dioxide to form silicon, the improvement comprising (a) contacting the by-produced gases from the silicon furnace with a cooling medium such as a vaporizing liquified hydrocarbon-containing gas or an expanding compressed hydrocarbon-containing gas to cool the by-produced gases and to cause silicon-containing materials to completely condense and to form agglomerated solids; (b) removing the agglomerated, solid materials from the gases, and (c) recovering value from the solids-free by-produced gases as an energy source or as a chemical intermediate.

Abstract: What is disclosed is a process for preparing silicon using a gas plasma as a heat source. The process comprises (a) generating a gas plasma in a reactor utilizing a transferred arc plasma configuration in which a minimum of gas is utilized to form a plasma; (b) feeding silicon dioxide and a solid reducing agent directly into the reactor and to the plasma; (c) passing the plasma gas, the silicon dioxide, and the solid reducing agent into a reaction zone of the reactor; (d) recovering molten silicon and the gaseous by-products.

Abstract: Silicon tetrachloride, hydrogen and metallurgical silicon are reacted at about 400.degree.-600.degree. C. and at pressures in excess of 100 psi, and specifically from about 300 up to about 600 psi to form di- and trichlorosilane that is subjected to disproportionation in the presence of an anion exchange resin to form high purity silane. By-product and unreacted materials are recycled, with metallurgical silicon and hydrogen being essentially the only consumed feed materials. The silane product may be further purified, as by means of activated carbon or cryogenic distillation, and decomposed in a fluid bed or free space reactor to form high purity polycrystalline silicon and by-product hydrogen which can be recycled for further use. The process results in simplified waste disposal operations and enhances the overall conversion of metallurgical grade silicon to silane and high purity silicon for solar cell and semiconductor silicon applications.

Abstract: A process is disclosed for the melt consolidation of silicon powder which is based on the use of a critical partial vacuum of 200-300 torr of an inert gas that is applied.

Abstract: A reactor apparatus (10) adapted for continuously producing molten, solar grade purity elemental silicon by thermal reaction of a suitable precursor gas, such as silane (SiH.sub.4), is disclosed. The reactor apparatus (10) includes an elongated reactor body (32) having graphite or carbon walls which are heated to a temperature exceeding the melting temperature of silicon. The precursor gas enters the reactor body (32) through an efficiently cooled inlet tube assembly (22) and a relatively thin carbon or graphite septum (44). The septum (44), being in contact on one side with the cooled inlet (22) and the heated interior of the reactor (32) on the other side, provides a sharp temperature gradient for the precursor gas entering the reactor (32) and renders the operation of the inlet tube assembly (22) substantially free of clogging. The precursor gas flows in the reactor (32) in a substantially smooth, substantially axial manner.

Abstract: A novel mixed binder system for agglomerates is disclosed. The agglomerates are suitable for use in the production of metals and alloys in a carbothermic reduction process such as the production of silicon in a direct arc furnace by the carbothermic reduction of silica. The agglomerates prepared using this mixture binder system have high physical strength over a wide temperature range. The mixed binder system consists essentially of a primary binder selected from the group consisting of coal tar pitch, asphalt, and petroleum pitch and a secondary binder selected from the group consisting of lignosulfonate salts, carbohydrates, and silicates.

Abstract: A process is disclosed for producing silicon, titanium, zirconium or uranium by reduction of a fluoro compound with sodium followed by leaching with an aqueous alkaline earth metal chloride and recovery of the sodium metal through electrolytic reduction.

Abstract: A method for producing silicon which comprises subjecting silane and chlorine to a combustion reaction to generate a flame and thereby precipitating fine crystals of silicon.

Abstract: A method and apparatus is disclosed for producing large particles of material from gas, or gases, containing the material (e.g., silicon from silane) in a free-space reactor comprised of a tube (20) and controlled furnace (25). A hot gas is introduced in the center of the reactant gas through a nozzle (23) to heat a quantity of the reactant gas, or gases, to produce a controlled concentration of seed particles (24) which are entrained in the flow of reactant gas, or gases. The temperature profile (FIG. 4) of the furnace is controlled for such a slow, controlled rate of reaction that virtually all of the material released condenses on seed particles and new particles are not nucleated in the furnace. A separate reactor comprised of a tube (33) and furnace (30) may be used to form a seed aerosol which, after passing through a cooling section (34) is introduced in the main reactor tube (34) which includes a mixer (36) to mix the seed aerosol in a controlled concentration with the reactant gas or gases.

Abstract: A process is disclosed for the production of elemental silicon that utilizes a non-reactive condensible gas as a means for purging the reactor of ambient air prior to the introduction of an alkali metal and a silicon tetrahalide.

Abstract: Apparatus for producing low cost, high purity solar grade Si wherein a reduction reaction, preferably the reduction of SiF.sub.4, by an alkali metal (Na preferred) is carried out by jetting a spray of reactants into a reaction chamber at a rate and temperature which causes the reaction to take place far enough away from the entry region to avoid plugging of reactants at the entry region and wherein separation in the melt is carried out continuously from the reaction and the Si can be cast directly from the melt. The melt separation is provided by openings in the reaction chamber wall between about 2 and 3.5 millimeters in width. The Si is retained within the reaction chamber due to its surface tension.

Abstract: An apparatus for producing low cost, high purity solar grade Si wherein a reduction reaction, preferably the reduction of SiF.sub.4, by an alkali metal (Na preferred) is carried out inside a reaction chamber. The chamber wall and bottom surfaces are formed of graphite and configured with drainage channels so as to facilitate the continuous separation of the products of reaction (Si and NaF) and removal of the molten salt by discharging the salt through one or more ports at the bottom of the reaction chamber. Such process is especially useful where it is desirable to discharge the reaction salt products from the reactor and retain silicon within the chamber for later removal.

Abstract: A method of manipulating the rate of homogeneous nucleation of silicon as either a particulate solid or liquid settling out of the gaseous phase during the pyrolysis of silane homologs by controlling the quantity of halogen within the pyrolysis medium. The rate of homogeneous nucleation can be maintained sufficiently low (below 1 silicon nucleus/cm.sup.3 /sec) so as to avoid power formation with a minimum amount of halogen.

Abstract: Process for producing low cost, high purity solar grade Si wherein a reduction reaction, preferably the reduction of SiF.sub.4, by an alkali metal (liquid Na preferred) is carried out essentialy continuously by injecting of reactants in substantially stoichiometric proportions into a reaction chamber having a controlled temperature thereby to form a mist or dispersion of reactants. The reactants being supplied at such a rate and temperature that the reaction takes place far enough away from the entry region to avoid plugging of reactants at the entry region, the reaction is completed and whereby essentially all reaction product solidifies and forms a free flowing powder before reaction product hits a reaction chamber wall. Thus, the reaction product does not adhere to the reaction chamber wall or pick up impurities therefrom. Separation of reaction products is easily carried out by either a leach or melt separation process.

Abstract: A process for producing trichlorosilane and equipment for practicing that process are disclosed. The process is a two stage process which combines the reaction of silicon tetrachloride and hydrogen with silicon with the reaction of hydrogen chloride with silicon. In one embodiment of the invention a two stage reactor is provided with a first stage heated to a temperature of about 500.degree.-700.degree. C. and a second stage maintained at a temperature of about 300.degree.-350.degree. C. Each of the first and second stages of the reactor are charged with silicon particles. A mixture comprising hydrogen and silicon tetrachloride are flowed through the silicon particles in the heated first stage to cause a partial hydrogenation of the silicon tetrachloride. The effluent from the first stage includes trichlorosilane and unreacted hydrogen and silicon tetrachloride. Hydrogen chloride is added to this effluent and the mixture of gases are passed through the silicon particles in the second stage of the reactor.

Abstract: A method for growing silicon single crystal uses as materials, silicon granules prepared by the silane process and having a residual hydrogen concentration of 7.5 wtppm or less, silicon granules prepared by the trichlorosilane process and having a residual chlorine concentration of 15 wtppm or less. In the case where such silicon granules are used, a bursting phenomenon does not occur when the silicon granules are melted. As a result, there is no scattered matter due to the bursting phenomenon, whereby the growth condition of the single crystal is not disturbed.