JPS6128604B2 - - Google Patents

Description

[Detailed description of the invention]

Recent developments in semiconductor work have increased the demand for extremely high purity, low cost, single crystal silicon, known as semiconductor grade silicon. Semiconductor silicon is used in the manufacture of semiconductor devices such as transistors, rectifiers, solar cells, etc. BACKGROUND OF THE INVENTION Hitherto, methods have been used to produce polycrystalline silicon for semiconductors, which can be converted into single crystal silicon for semiconductors, by a special method such as the well-known Cziochoralski method. One such conventional method involves purifying, for example, silicon tetraiodide by crystallization, vaporizing it, and then depositing the silicon from the vapor onto a hot wire of a relatively inert metal such as tungsten. let In this conventional method, due to the difference in the volatility of silicon and iodine, the iodine vapor, the reaction product, diffuses away from the area near the hot wire, and silicon is deposited and grows on the hot wire, forming a crystalline form. Forms significant clumps of silicone. When growth reaches a certain stage,
A cooled mass of crystalline silicon is cut in layers from a linear substrate. Another conventional method for preparing polycrystalline silicon for semiconductors is to react highly purified superheated silicon tetrachloride with extremely hot zinc vapor, resulting in interaction between the zinc vapor and silicon tetrachloride. A heated silicon substrate is prepared, and elemental silicon is grown on the heated silicon substrate from zinc vapor and silicon tetrachloride to produce polycrystalline elemental silicon. Under appropriate conditions, at least a portion of this silicon becomes semiconductor grade. Traditionally, silicon halides were reduced with hydrogen in a furnace and the mixture was slowly passed through a heated quartz glass tube inside the furnace.
Polycrystalline silicon for semiconductors was manufactured. Silicon is deposited on the inner surface of the heated tube, and the tube is removed from the furnace from time to time to recover the silicon. Currently, polycrystalline silicon for semiconductors is covered by a U.S. patent.
As stated in Nos. 3053638 and 3240623,
Trichlorosilane SiHCl ₃ or silicon tetrachloride
It is made by a chemical vapor deposition method in which SiCl ₄ is reduced with hydrogen on a heated silicon substrate. In this method, trichlorosilane and silicon tetrachloride are prepared from commercial or metallurgical silicon of approximately 98% purity and purified by fractional condensation. Conventional methods have demonstrated that it is technically and economically possible to produce high-purity polycrystalline silicon of a quality suitable for use in semiconductors by reducing halosilane with hydrogen. Currently, all commercial polycrystalline silicon for semiconductors is produced by the chemical vapor deposition method described above, in which dichlorosilane or trichlorosilane is reduced with hydrogen and deposited on an electrically heated silicon filament substrate. Silicon is deposited on top. The silicon filament substrate is heated by electrical resistance heating.
The walls of the chamber, which is kept at a temperature higher than 1000°C and filled with the filament and reaction gas, are kept at a temperature of about 300°C to prevent silicon from depositing on it. As this process progresses, the heated substrate thickens to a diameter of approximately 7.62 to 10.15 cm. The process is then interrupted and the substrate is removed from the chamber. The substrate can be up to 121.92 cm in length, and after being removed it is turned into a rod as a new starting material.
This may have a diameter of, for example, 0.3175 to 1.27 cm. Generally, in conventional processes, the effluent gas of a continuous vapor deposition reactor is not recycled but is disposed of by appropriate means. Conventional continuous steam deposition processes require large amounts of electrical energy to operate, on the order of 800 to 1000 kilowatts per kilogram of silicon produced. Since a large number of reaction chambers and silicon substrates are required, the invested capital and labor costs are also high. Production costs in factories producing at rates of 300 to 500 metric tons per year currently range from $25.00 to $30.00 per kilogram. The current market price is approximately $65.00 per kilogram. Currently, supply and demand in the semiconductor industry are balanced. Recently, there have been periods of severe shortages, and there is a potential for new, large demand to be created that will be many times greater than the current demand in the semiconductor industry. This new demand is the use of silicon solar cells to photovoltaically convert solar energy into electrical energy. In order to realize and meet this potential new demand, the manufacturing cost of silicon for semiconductors must be reduced per kilogram.
substantially less than $10.00 and increase the efficiency of converting solar energy into electrical energy.
It is necessary to maintain the quality of silicon. It is an object of the invention to provide a method and a device which meet the above-mentioned needs and criteria. This invention significantly reduces energy requirements and provides a continuously operated process in which reactor effluent gas is recovered, separated and recycled. In particular, the by-product hydrogen halide of the process of this invention is recycled to produce a purified silane feed to the reduction reactor, and the hydrogen is also recovered and recycled.
The only raw material consumed in the method of this invention is low cost metallurgical silicon. In this invention, the residence time of the reactant is 0.01 to 0.1.
Provides a simple continuous flow reduction reactor that is short, on the order of seconds. The reactants and nucleating agent are preheated separately in an efficient beam-shot gas-fired heat exchanger. The product is in the form of granules ranging from 10 to 100 mesh. This results in a large volumetric capacity in a small tubular reactor, as well as continuous operation and continuous product removal, which requires less capital investment and less time than traditional continuous steam deposition methods. The cost will gradually become cheaper. The continuous flow reduction method of the present invention provides a relatively inexpensive mass production means for continuously producing silicon for semiconductors. In the examples to be described, impure (metallurgical) silicon is converted to a volatile halosilane intermediate compound by the chemical reaction described below.

[Table] In this specification, the term halosilane means
It is used as containing SiX ₄ HSiX ₃ , H ₂ SiX ₂ and H ₃ SiX ₃ and is represented by the general formula H _o SiX _(4-o) . Here, X is Cl, Br or I. Impurities in the form of halides are separated and eliminated from the halosilane intermediate by fractional condensation in the process of this invention. The purified volatile halosilane intermediate is then preheated and reduced with purified preheated hydrogen according to formulas (2) and (4) in a continuous flow tubular reactor. Purified semiconductor grade polycrystalline silicon is separated from the reactant gas and solids streams and recovered. Hydrogen halide as a reaction product is separated from the reaction gas stream and recycled to convert more metallurgical silicon to crude intermediate silicon compounds and hydrogen. Therefore, the method of this invention consumes impure silicon,
Pure silicon is produced and impurities are eliminated as liquid or solid halides. FIG. 1 shows reacting in the vapor phase a halosilane intermediate and hydrogen that have been separately preheated to a temperature above the reaction temperature of the intermediate in a continuous flow reduction reactor;
2 is a schematic diagram illustrating the various steps of an embodiment of the method of the invention for continuously producing high purity silicon by separating the reaction gas from the resulting silicon in a cyclone separator; FIG. . The silicon is continuously released from the bottom of the separator, and the reactant gas is released from the top of the separator and used again. This invention describes a novel method and reaction method for continuously producing ultra-high purity polycrystalline silicon in large quantities at low cost by reducing halosilane BiH _o x _4-o with hydrogen H ₂ in the vapor phase. Provide utensils. Silicon produced by the method of this invention has uniform particle size and ultra-high purity, so it can be used for melting and pulling single crystal silicon used in the production of semiconductor devices, including integrated circuits, solar cells, etc. Particularly suitable for When carrying out this invention, halogen X ₂ or hydrogen halide HX is produced in refiner 3, and
At elevated temperatures in the range of 800° C., the silicon halide generator 5 reacts with silicon containing small amounts of impurities to produce crude halosilane SiH _o x _4-o intermediates, such as silicon halide SiX ₄ . The silicon introduced into the generator 5 is, for example, metallurgical silicon. Commercial 98.5% silicon produced by generator 2 or high purity 99.9% silicon can be used. Generator 2 may be a well-known electrothermal silicon generator. By fractional condensation, hydrogen halides of higher purity are obtained from commercial products in Refineer 3.
HX is obtained. The silicon halide from the generator 5 is purified by fractional condensation in the rear iner 6.
In this refiner, impurities that have entered the process as impure silicon are converted into metal halides and removed by fractional condensation or the like. The refiner 6 may be of the type described in detail in US Pat. No. 3,020,128. Purified silicon intermediate compound is heated to 900 to 900 in preheater 8.
It is preheated to an elevated temperature in the range of 1100°C and is injected into a continuous flow reduction reactor 10 of the type shown in FIG. This will be explained in more detail later. Preheater 8 may be of the gas-ignited type. Hydrogen _H2 from commercial sources as well as generator 5
The recycled hydrogen from the hydrogen refiner 1 is produced in high purity by conventional methods. This refiner may also be of the type described in US Pat. No. 3,020,128. Purified hydrogen is heated to 900 to
Preheated to a high temperature within the range of 1500℃. This preheater may be similar to preheater 8, in which preheated hydrogen is injected into continuous flow reduction reactor 10, where it is produced and separately preheated in such a way as to cause an instantaneous chemical reaction. The mixture is thoroughly mixed with the silicon intermediate compound. High purity preheated silicon particles of selected dimensions, e.g. removed from a cyclone solid-gas separator 11, are transferred to a continuous flow reduction reactor 10 by a flow of hydrogen in the manner described hereinafter.
injected into. Although the silicon particles may catalyze hydrogen reduction of the vapor phase of the silicon intermediate, they primarily promote silicon nucleation and growth while the reactants flow through the continuous flow reduction reactor 10. It is a purpose.
This phenomenon is due to the large hot surface of the silicon particles and the favorable Gibbs free energy of the reactants in the continuous flow reduction reactor. The solid and gaseous reactant stream, after a suitable residence time in the continuous flow reduction reactor 10, is passed directly to a cyclonic solid gas separation 11 where silicon particles are collected and removed from the gas stream. It is separated and then discharged from the bottom of the separator. The gas stream is discharged from the top of the cyclone separator 11 in the conventional manner and then passed through a gas cooler, condenser and scraper system. In the gas stream from separator 11, condensable material consisting of unreacted halosilanes and HX is transferred to device 14.
Separated by condensation, absorption and fractional condensation. The halosilane thus separated is circulated to the preheater 8. The hydrogen halide thus separated is sent to the generator 5, where it reacts with other impure silicon to further produce intermediates and hydrogen.
The H ₂ generated in the generator 5 is circulated to the hydrogen refiner 1 as previously described. The non-condensable gas in the gas stream exiting the separator 11 is unreacted hydrogen _H2 , which is recycled to the hydrogen refiner 1 after scraping in cold HX liquid. A small portion (approximately 10%) of the hot silicon particles discharged from the cyclone separator 11 is appropriately reduced in particle size and then circulated to the preheater 15 where it is subjected to a continuous flow reduction reaction by the flow of preheated hydrogen. Injected. The remaining hot silicon particles coming out of the separator 11 are gradually added to a molten pool of metallic silicon provided below the separator, from which monocrystalline silicon is continuously pulled. Another method is to cool the silicon particles coming out of the separator 11 and store it for current use. The impurities introduced into the process of this invention in the raw materials used are mainly those found in impure silicon, which, as mentioned earlier, is mainly converted into metal halides and then processed by fractional distillation. , separated from the crude halosilane intermediate. The waste stream containing metal halides may be disposed of as waste or treated in conventional manner to recover the halides and impurities. How the impurities are ultimately disposed of depends primarily on their quantity and the commercial value they contain. A continuous flow reduction reactor 10 and a cyclone solid gas separator 11 are shown schematically in FIGS. 2 and 3. From silicon halide preheater 8
SiX ₄ is introduced into the injection mixer 20 via the inlet 11. Hydrogen flow from the hydrogen preheater 9 enters the inlet 22
is introduced into the mixer 20 via. The silicon particles from separator 11 are fed into hopper 23 and the contents of the hopper are injected into the hydrogen stream via rotary valve 24. A mixer 20 is connected to the tubular reactor 25. This reactor has a diameter of e.g.
The length may be between 609.6 and 1219.2 cm. The opposite end of the tubular reactor 25 is connected to a cyclone separator 26 of known construction. The apparatus shown in FIG. 2 continuously produces polycrystalline silicon by reducing silicon halide or halosilane with hydrogen at high temperatures in the vapor phase. This device separates silicon halide or halosilane vapor (preheater 8 in Figure 1), hydrogen gas (hydrogen preheater 9 in Figure 1) and silicon particles (preheater 15) to temperatures above 900°C. It constitutes a means for preheating. The apparatus also has a tubular reactor 25 containing a mixer 20. The mixer may be a jet nozzle mixer, into which the reactants and nucleating agent are injected and intimately mixed in such a way that an instantaneous chemical reaction occurs. A mixer is connected directly to the tubular reactor 25, where nucleation and growth of silicon particles takes place. The apparatus also includes a cyclone solid gas separator 26 through which the reactant gas and silicon particles are passed to collect and separate the silicon particles from the gas stream. The main feature of the continuous flow reduction reactor advantageously used in the process of this invention is that the reactants and nucleating agent are
It is preheated separately to a high temperature within the range of 1200°C, and the reactants and nucleating silicon particles are injected and mixed at high speed. The reactor design, temperature, and flow rate of the reactants are such that the reactants, nucleating agent, and reaction products are maintained for a period of time such that substantially the theoretical maximum conversion takes place and maximum dimensional growth of the silicon particles occurs. It is important to remain within the reaction zone during this time.
Generally, a residence time of about 0.01 to 0.1 seconds is sufficient. It is also important to preheat the silicon particles to the highest usable temperature of about 1200° C. in order to promote nucleation of the silicon from the vapor phase and growth of the silicon particles on the surface as a nucleating agent. The high velocity, turbulent flow of reactants through the jet mixing nozzle 20 and the tubular reactor 25 provides high volumetric flow rates within the small diameter tubular reactor. Particularly when the tubular reactor 25 is arranged along a horizontal axis, high gas flow velocities are necessary to keep the silicon particles in uniform suspension. In addition to providing a large nucleation surface, the silicon particles serve to scrub the inner walls of the reactor and prevent silicon particles from depositing thereon. Because of its dual purpose as a nucleating agent as well as this abrasive agent, it is advantageous to use silicon particle sizes in the range of -10 to +100 mesh. Example 1 High purity silicon tetrabromide vapor from a continuous source is fed at a rate of 0.49 liters per second into a preheater where it is heated to a temperature of 1090°C and then heated to a temperature of 25 mm i.d.
into a horizontal tubular reactor 6. The reactor is 6 meters long and is equipped with a mixing nozzle head and a cyclone solid gas separator approximately as shown in FIG. High purity hydrogen from a continuous source is pumped at a rate of 8.67 liters per second into a preheater where it is heated to a temperature of 1090°C before being pumped into the head of a tubular reactor where it When mixed intimately with silicon oxide vapor, it reacts to produce silicon and hydrogen bromide. Pure frame silicon particles in the range of -10 to +40 mesh BSS from a continuous source are preheated to a temperature of 1100 °C and 0.3 m/s
grams into the heated hydrogen stream as it enters the mixing head of the tubular reactor. The entire mass of gas and solids participating in the reduction reaction is
It flows continuously through a tubular reactor at a high velocity of about 100 meters and enters a cyclone separator. The average residence time in the tubular reactor is approximately 0.06 seconds. High purity silicon particles are separated from the gas stream,
It is discharged from the separator at a rate of 0.68 grams per second.
This gives a net yield of 0.38 grams per second. Summary SiBr ₄ 0.49 liters/second H ₂ 8.67 liters/second Nucleating agent Si 0.3 grams/second Product Si 0.68 grams/second Net Si 0.38 grams/second Preheating temperature SiBr ₄ 1090℃ H ₂ 1090℃ Si 1100℃ Reaction The velocity in the vessel is 100 m/s.Example 2 Using the same type of equipment as in Example 1, high purity tripromsilane vapor from a continuous source is fed into a preheater and heated to 955°C. It is then pumped into a tubular reactor at a rate of 0.49 liters per second. High purity hydrogen from a continuous source is pumped into a preheater to heat it to 955°C and then pumped into a tubular reactor at a rate of 8.67 liters per second. -10 to +100 from continuous source
Pure silicon particles within the range of mesh BSS
It is preheated to a temperature of 1100°C and fed at a rate of 0.1 grams per second into the heated hydrogen stream as it enters the mixing head of the tubular reactor. The entire reactant, consisting of gases and solids, passes through a tubular housing at a velocity of the order of 100 meters per second and enters a cyclone separator. High purity silicon particles are separated from the gas stream and expelled from a cyclone separator at a rate of 0.48 grams per second. Therefore, the net yield is
It is 0.38 grams. Summary HSiBr ₃ 0.49 liters/second H ₂ 8.67 liters/second Nucleating agent Si 0.1 grams/second Product Si 0.48 grams/second Net Si 0.38 grams/second Example 3 In this case, the temperature is the same as Example 2, The speed in the reactor is 100 meters/second. HSiCl ₃ 29.4 liters/minute H ₂ 520 liters/minute Nucleating agent Si 60 grams/minute Product Si 87.6 grams/minute Net Si 27.6 grams/minute Example 4 The temperature is the same as in Example 1; The speed is 200 meters/second. HSiCl ₃ 58.8 liters/min H ₂ 1040 liters/min Nucleator Si 120 grams/min Product Si 147.8 grams/min Net Si 27.8 grams/min Having illustrated a particular embodiment of the process of this invention,
Needless to say, many changes can be made. It is to be understood that the following claims are intended to cover all possible modifications within the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic representation of one embodiment of the process of the invention; FIG. FIG. 3 is a plan view of the separator shown in FIG. 2. Explanation of main symbols, 8...Silicon halide preheater, 9...Hydrogen preheater, 10...Continuous flow reduction reactor.

Claims (1)

[Claims] 1. Preheating hydrogen to a temperature higher than 500°C, preheating an intermediate selected from the group consisting of silicon halides and halosilanes to a temperature higher than 500°C,
The preheated intermediate is allowed to react with the preheated hydrogen in the vapor phase, the preheated intermediate and the preheated hydrogen are mixed, and the preheated intermediate is reacted with the preheated intermediate by a continuous flow recirculation method. A method for producing high-purity silicon that consists of a process in which silicon is separated from steam by reduction with preheated hydrogen. 2. A method for producing high-purity silicon according to claim 1, which includes a step of introducing a flow of silicon particles that act as nuclei of silicon generated during the reduction step during the reduction step. . 3. In the method for producing high-purity silicon recited in claim 1, the intermediate is tribromosilane.
A method for producing high-purity silicon, SiHBr ₃ . 4 In the method for producing high-purity silicon described in claim 1, the intermediate is silicon tetrabromide.
A method for producing high-purity silicon, which is SiBr ₄ . 5. A method for producing high-purity silicon according to claim 1, which includes a step of recovering a reaction gas from the process and separating the reaction gas for reuse in the process. 6. A method for producing high-purity silicon according to claim 1, which includes a step of reacting a halogen or a halogen acid with metallurgical silicon to form the intermediate. 7. The method for producing high-purity silicon according to claim 6, wherein the halogen is bromine. 8 In the method for producing high-purity silicon described in claim 6, the halogen acid is hydrobromic acid HBr.
A manufacturing method for high-purity silicon. 9. In the method for producing high-purity silicon as claimed in claim 1, a preheated intermediate and preheated hydrogen are rapidly introduced into a tubular reactor, and a reactant is rapidly introduced into the reactor. A method for manufacturing high-purity silicon that involves intimate mixing and reaction. 10. A method for producing high-purity silicon according to claim 1, which includes a step of reacting hydrogen halide with metallurgical silicon to form the intermediate. 11 In the method for producing high-purity silicon described in claim 1, hydrogen is preheated to a temperature within the range of about 900 to 1200°C, and the halosilane intermediate is heated to a temperature of about 900°C to 1200°C.
A process for producing high purity silicon comprising preheating to a temperature in the range from 1200°C to 1200°C and injecting and mixing the separately preheated intermediate and hydrogen in a continuous stream into a mixer. 12. A method for producing high-purity silicon as claimed in claim 2, wherein the step of introducing a stream of silicon particles comprises injecting the particles into a common stream of preheated hydrogen. .