JP2007126342A - Method of manufacturing silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing silicon in which high purity silicon is prepared by reduction of silicon tetrachloride with zinc; and also to provide a device which enables separation and extraction of silicon alone by dissolving high purity silicon generated by vapor-phase reaction in a system and by substantially excluding separation processes from other reactants. <P>SOLUTION: The device is for manufacturing silicon to obtain high purity silicon by reducing silicon tetrachloride with zinc in a vapor phase and the following manufacturing steps are performed: (1) the step of generating zinc gas; (2) the step of supplying the zinc gas into a reaction column; (3) the step of injecting silicon tetrachloride gas into the flow of the zinc gas in the reaction column; (4) the step of generating silicon by the reaction of the zinc gas and silicon tetrachloride in the reaction column: (5) the step of colliding the reactant gas containing silicon to a wall kept at a temperature above the melting point of silicon for silicon dissolution; (6) the step of leading liquid silicon to a silicon storing tank situated below; (7) the step of separating zinc from a residual reactant gas coming out of the reaction column by cooling the residual reactant gas to liquefy zinc while returning the liquefied zinc to the step of producing zinc gas; and (8) the step of taking out zinc chloride which is generated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention mainly relates to an apparatus for producing silicon for obtaining high-purity silicon by reducing silicon tetrachloride, which can obtain silicon used for solar cells and electronic components with low energy consumption, with metallic zinc.

  High-purity silicon is produced by treating crude silicon with hydrogen chloride and hydrogen to produce trichlorosilane, or sometimes dichlorosilane or monochlorosilane, and using these silane compounds as raw materials by chemical vapor deposition. It is manufactured. With this method, extremely high-purity silicon can be obtained, but at the stage of producing each silane compound as an intermediate substance, the yield of the target silanes tends to be the most stable silicon tetrachloride and is 50% or less. In addition, since the reaction for silicon generation is extremely slow, the equipment is large and the equipment investment is extremely large, and the power required for production is considered to be as large as 350 kWh / kg-silicon even for polycrystalline silicon. . Such silicon is good for highly integrated and high-value added electronic devices, but it is too high quality for use in solar cells and so-called IC-tags that will be required in large quantities in the future, and is necessary for manufacturing. The energy is too large and the manufacturing cost is too large for the intended solar cell. Furthermore, this process produces a large amount of silicon tetrachloride as a by-product. Silicon tetrachloride by this has been used for quartz glass raw materials by being decomposed with water conventionally, but it has become excessive with the increase of silicon production, along with the yield problem of crude silicon raw materials It has become difficult to balance.

As an alternative method for producing silicon, a method using silicon tetrachloride as a raw material has been proposed for a long time. That is, this is a method for producing high-purity silicon by reducing silicon tetrachloride with zinc metal at a high temperature. In the 1950s, it was assumed that DuPont USA was put into practical use, where silicon tetrachloride and zinc were reacted in the gas phase at a temperature of 950 ° C. to obtain solid high-purity silicon. In this method, extremely high-purity silicon is said to have been obtained, but it was considered that there was a problem with the separation from zinc chloride obtained as one of the reaction products, and the so-called Siemens method described above was used. It is said that the production was stopped with the completion of the silicon manufacturing method by CVD using trichlorosilane (SHCl ₃ ) as a raw material. On the other hand, JP-A-11-060228 and JP-A-11-092130 show methods for obtaining high-purity silicon by reacting molten zinc with silicon tetrachloride gas. It had to be separated from zinc chloride, which was complicated and left a problem of contamination by impurities during the separation operation.

The present inventors disclosed in Japanese Patent Application Laid-Open No. 2004-210594 high-purity silicon by taking out only silicon in solid or liquid form as a raw material and by-product by a high-temperature gas phase reaction in which silicon tetrachloride gas is reduced with zinc gas. Have gained. In that case, the energy consumption was successfully reduced to about 1/9 of the energy required for high-purity silicon production by the so-called Siemens method. In connection with these, the inventions of JP-A-2003-342016, JP-A-2004-010472, JP-A-2004-035382, JP-A-2004-099421, JP-A-2004-284935 and the like have been carried out. Although it is slightly inferior, it has been confirmed that both polycrystalline and single crystals are sufficient for solar cells, and in the case of single crystals, they can be used sufficiently for electronic devices other than special applications. These are mainly continuous devices for obtaining high-purity silicon from closed crude silicon. When SiCl4 is already present, a simpler and easier-to-handle manufacturing device is required.

Japanese Patent Laid-Open No. 11-060228 Japanese Patent Laid-Open No. 11-092130 Japanese Patent Laid-Open No. 2004-210594 JP 2003-342016 A JP 2004-010472 A JP 2004-035382 A JP 2004-099421 A JP 2004-284935 A

The present invention is a silicon production apparatus for obtaining high-purity silicon by zinc reduction of silicon tetrachloride, dissolving high-purity silicon produced by a gas phase reaction in the system, and substantially eliminating the separation operation from other reaction components. An object of the present invention is to provide an apparatus capable of separating and taking out only silicon.

The present invention is a silicon production apparatus for obtaining high-purity silicon by reducing zinc tetrachloride in the vapor phase. 1. a process for producing zinc gas; 2. feeding the zinc gas into the reaction tower; 3. blowing silicon tetrachloride gas into the flow of zinc gas in the reaction tower; 4. a step in which zinc gas reacts with silicon tetrachloride in a reaction tower to produce silicon; 5. a process in which the reaction gas containing silicon collides with a silicon melting wall held above the melting point of silicon; 6. a step of introducing liquid silicon into a silicon holding tank located underneath; 7. a step of cooling the remaining reaction gas from the reaction tower to liquefy and separate zinc in the remaining reaction gas and returning it to the zinc gas production step; A high-purity silicon production apparatus comprising a step of taking out generated zinc chloride, leveling pressure fluctuations that may occur in the system, and causing silicon generated in a solid or semi-melt to collide with a hot wall in the system As a result, it was possible to keep the energy consumption small despite the high temperature reaction, and to minimize impurities in the generated silicon.

As shown by SiCl ₄ + 2Zn + Si + 2ZnCl ₂ , silicon generation by zinc reduction of silicon tetrachloride is, in the case of a gas phase reaction, the melting point of silicon is 1410 ° C. As a result, a fluctuation in pressure becomes a problem.

The present invention has been to prevent the pressure fluctuation in the manner substantially the 2Zn → 2ZnCl ₂ by such blown from outside of the system silicon tetrachloride in consideration to a gas phase reaction that reduction reaction is very fast . That is, after zinc metal is dissolved and gasified in advance, the zinc gas is supplied to the reaction tower so as to create a fast swirl flow if possible. Of course, it is also possible to send a mixed gas of zinc gas and zinc chloride gas instead of zinc gas. Silicon tetrachloride is blown into this. That is, these mixed gas and zinc gas are previously generated outside the reaction tower, heated to a reaction temperature or an appropriate temperature close to the reaction temperature, and supplied to the reaction tower. When the heated silicon tetrachloride gas is blown into the reaction tower having such a gas flow, in addition to the extremely fast reaction, the chance of association in such a flow increases, so the reaction is almost instantaneously completed. Thus, silicon is generated in a solid or semi-liquid state, and the reaction gas becomes zinc chloride gas. In this reaction, it is necessary to make the zinc excessive, which stabilizes the reaction and prevents side reactions from occurring at all.

The temperature of the reaction is preferably 1100 ° C. to 1350 ° C., that is, below the melting point of silicon, and as a result, extremely silicon produced by the gas phase reaction is partially produced as a semi-melt and partially as a solid due to the melting point drop. Grows in the reaction tower without seed crystals and becomes fine single crystal or polycrystalline fibrous or dendritic silicon. It is considered that this growth process is highly separated from metallic zinc gas or zinc chloride gas, which is a reaction gas, so that the purity becomes higher. This reaction can be carried out at a temperature higher than the melting point of silicon. In this case, however, the yield of the silicon deteriorates because the generated silicon melt is a fine droplet or it is difficult to separate from the gas phase. It tends to adversely affect the subsequent separation process. In addition, this reaction proceeds even at a low temperature of 1100 ° C. or lower, but the reaction is slightly slow, so that the growth of silicon crystals generated in the gas is not likely to occur sufficiently, and zinc and zinc chloride are slightly mixed in. A decrease in purity may occur.

In this reaction, bimolecular gas is substantially formed from bimolecular gas, so there should be no pressure change. However, in reality, since each vapor pressure is different, a pressure increase substantially occurs. This pressure increase and subsequent separation, or reduced pressure associated with temperature change due to the liquefaction process, accelerates the movement of the gas, and the gas moves to the fusion process with silicon at a faster rate. In the fusing process, the direction of the fluid is changed, but a gas having a small moment of inertia follows a change in direction, whereas a solid moves so as to collide with a hot wall. As a result, the silicon, which is selectively solid and becomes highly purified, collides with the wall of the fusing step where the wall temperature is maintained at 1450 ° C. to 1600 ° C., which is higher than the melting point of silicon, and melts. At this time, the silicon is in the form of fibers or fine dendrites, and since it has a large surface area, it is easily melted and held in the lower silicon holding tank along the wall of the melting process section. In this part, the gas passes through the reaction column at a high speed, so that the temperature rise is minimized.

In the melting process, an external heating method in which the reaction tower wall is heated from the outside may be used, but in order to cause heat concentration, reduce energy consumption, and to minimize the rise in the temperature of the gas part. Has a heating element inside, for example, a high-frequency induction heating method is more preferable, and the heating part is preferably conductive silicon carbide or graphite having a silicon carbide surface. The conditions for high-frequency induction heating are not particularly specified, and it is sufficient that the temperature can be raised to the target temperature.

The gas from which the silicon has been separated in the melting step is sent to the zinc separation step while the temperature is lowered. This driving force is a pressure change caused by the temperature change described above. Since zinc chloride has a melting point of 704 ° C. and zinc has a melting point of 907 ° C., during this temperature, zinc is separated from zinc chloride as a liquid, but actually has a vapor pressure, so 650 ° C. to 750 ° C. While the gas is rotated in a cyclone manner at a temperature of zinc, the zinc is collected as droplets and collected as liquid zinc in the lower part of the cyclone, but other methods may be used. For example, this gas may be struck against a wall held at 650 ° C. to 750 ° C. to separate zinc as a liquid, and zinc chloride may be sent as a gas to the next process. The temperature specified here is partly set lower than the boiling point of zinc chloride, in order to improve the separation of zinc. Furthermore, in this temperature range, the zinc chloride gas from the gas phase is substantially not emitted, and the portion that has come out is separated from zinc as a liquid, so that the zinc is separated and returned to the zinc liquefaction process. In the conversion step, it is sent to the reaction tower as a gas and used again for reducing silicon tetrachloride. The zinc chloride slightly separated is sent to the zinc chloride removal step.

The zinc chloride gas from which zinc has been removed in the zinc separation step is further lowered in temperature and taken out as a melt. In addition, a part of zinc chloride used as a melt can be gasified again as necessary and returned to the reaction tower as an atmospheric gas. The remaining zinc chloride may be commercialized as zinc chloride, or may be separated into zinc and chlorine by electrolysis and returned to the reaction step.
In this way, high-purity silicon is obtained from silicon tetrachloride. The above is one embodiment, and it goes without saying that each process may work with a different mechanism in the manufacturing apparatus including the above-described process. is there.

According to the present invention, high purity silicon can be obtained at a very high reaction rate using silicon tetrachloride as a raw material, which can be obtained very easily as a raw material, or has been a problem in handling as a conventional byproduct. In addition, the reaction speed is extremely fast, so it is possible to use a small facility. At the same time, there is a substantial refining effect in the process, so it can be highly purified, and the product silicon can be made into a liquid to enable continuous operation. It has the effect of being.

FIG. 1 shows a flow of the silicon manufacturing apparatus of the present invention. As shown here, it has a simple structure, and the temperature of the melt process is higher than the melting point of silicon. The other parts are almost equal to or lower than 1250 ° C. of the conventional Siemens CVD process, and the reaction rate is extremely high. So energy consumption is extremely low. Although the material of the process shown here is not particularly specified, it is desirable that the reaction tower portion and the melting step portion are made of quartz glass, and since there is an excess of zinc gas, there is almost no consumption and no contamination of impurities occurs. It has been confirmed.

FIG. 2 shows a flow of a silicon manufacturing apparatus in which zinc chloride is incorporated into the process as an atmospheric gas. By incorporating zinc chloride gas into the process, the scale of the equipment is slightly increased, but the pressure fluctuation in the system is reduced, the reaction rate is optimized, and the product silicon can be purified to a higher degree.
Although it shows by an Example below, it cannot be overemphasized that it is not limited to this.

Silicon was manufactured using the silicon manufacturing apparatus shown in FIG. In other words, high-purity zinc (corresponding to 6-nine) obtained by melting salt electrolysis of zinc chloride obtained in this step as a raw material was dissolved in the zinc dissolution step, and the quantitative amount was continuously sent to the gasification step. . The temperature of the gasification step was 1000 ° C., and the gasified zinc was 1200 ° C. while further raising the temperature, and was sent to the reaction tower maintained at 1200 ° C. A gas was blown into the cylindrical reaction tower so as to create a gas flow in the circumferential direction, and the gas was fed from the reaction tower to the silicon melting step with a slight positive pressure. The amount of zinc gas supplied was 1.5 times the theoretical amount required for silicon tetrachloride reduction so that the zinc gas was always excessive. Silicon tetrachloride was re-distilled from commercially available 4-nine grade to 6-nine, gasified in the gasification step, and injected into the reaction tower at about 1.5 atm. In the injection process, a plurality of holes were made in a quartz glass tube, and the direction of the holes was set to the circumferential direction so as to give a rotational motion in the reaction tower. This resulted in zinc chloride white smoke immediately after injection, which increased the gas volume and moved it to the melting tank held at a low pressure, and the silicon dropped downwards as droplets. . The reaction gas composed of zinc and zinc chloride was sent to a cyclone-type zinc separation tank while the temperature was lowered from the bypass to separate the zinc, and the zinc chloride was melted in the zinc chloride recovery section. The temperature of the zinc separation part was 700 ° C., and almost no zinc chloride was observed in the liquefied zinc. When the temperature was lowered to 650 ° C., a slight amount of zinc chloride was observed on the surface of the melt zinc. It was found that the silicon thus obtained had a purity of 6-nine 5 or more and can be used as it is as solar cell silicon.

Silicon was manufactured using the silicon manufacturing apparatus of FIG. This apparatus is obtained by adding a zinc chloride gasification step to the silicon production apparatus used in Example 1, and sending a mixed gas of zinc gas and zinc chloride gas instead of zinc gas. Zinc chloride was added dropwise to the zinc evaporation section so that the melt extracted from the system was almost quantitatively mixed with zinc gas as zinc chloride gas, and the temperature was set to 1250 ° C. and sent to the reaction tower. The amount of zinc chloride gas was set to be almost the same as that of zinc gas by volume. Silicon tetrachloride gas was fed in under the same conditions as in Example 1, but the supply amount was set to 1/2 that of Example 1 in accordance with the zinc gas. Silicon was produced under the same conditions as in Example 1 except that the reaction tower temperature was 1250 ° C., that is, the reaction temperature was 1250 ° C. The temperature of the zinc separation step was 650 ° C. As the amount of zinc chloride gas in the reaction gas increased, the zinc chloride recovery process became complicated, and a slight amount of zinc chloride was mixed in the separated zinc, but instead the zinc in the recovered zinc chloride was drastically reduced. The generated silicon melt was solidified in a crucible and analyzed after acid cleaning. As a result, it was found that it was between 6-nine 5 and 7-nine, and it was slightly purified.

Industrial applicability

It is a high-purity silicon manufacturing device that improves the ground-breaking energy saving and productivity of silicon, mainly solar cells that will be required in large quantities in the future, mainly for solar cells as single crystals and polycrystals, and ICs. It greatly contributes to the production of silicon used for electronic devices such as tags, and is expected to be used for such applications.

It is the figure which showed the structure of the manufacturing apparatus of the silicon concerning this invention. It is the figure which showed another structure of the silicon manufacturing apparatus concerning this invention, and uses the mixed gas of zinc chloride and zinc as atmospheric gas.

Explanation of symbols

1 Reaction Tower 2 Zinc (Zinc + Zinc Chloride) Gas Supply Port 3 Silicon Tetrachloride Gas Supply Port 4 Zinc-Silicon Tetrachloride Reaction Portion 5 Silicon Precipitation Portion 6 Silicon Melting Portion 7 Silicon Melting Portion Hot Wall 8 Generated Silicon Storage Tank 9 Zinc Liquefaction Separation part 10 Zinc chloride liquefaction part 11 Zinc liquefaction part 12 Zinc gasification part 13 Zinc chloride storage tank 14 Zinc raw material storage tank 15 Silicon tetrachloride gasification part 16 Silicon tetrachloride raw material storage tank 17 Zinc chloride gasification part

Claims (15)

1. A silicon production apparatus for obtaining high-purity silicon by reducing zinc tetrachloride in a gas phase. 1. a process for producing zinc gas; 2. feeding the zinc gas into the reaction tower; 3. blowing silicon tetrachloride gas into the flow of zinc vapor in the reaction tower; 4. a step in which zinc vapor reacts with silicon tetrachloride in a reaction tower to produce silicon; 5. a process in which the reaction gas containing silicon collides with a silicon melting wall held above the melting point of silicon; 6. a step of introducing liquid silicon into a silicon holding tank located underneath; 7. a step of cooling the remaining reaction gas from the reaction tower to liquefy and separate zinc in the remaining reaction gas and returning it to the zinc gas production step; A high-purity silicon production apparatus comprising a step of taking out generated zinc chloride. 2. The silicon manufacturing apparatus according to claim 1, wherein the zinc gas is a mixed gas of zinc gas and zinc chloride gas. 3. A silicon manufacturing apparatus according to claim 1, further comprising a step of supplying zinc chloride gas. 4. The silicon production apparatus according to claim 1, wherein the zinc gas sent to the reaction tower advances in the reaction tower while being swirled in the tower. 5. The silicon production apparatus according to claim 1, wherein the silicon tetrachloride is vaporized and heated in advance and sent to the reaction tower in a pressurized state. 6. The silicon production apparatus according to claim 1, wherein the reaction tower temperature is 1100 ° C. to 1350 ° C. 7. A silicon production apparatus according to claim 1, wherein a baffle plate is provided between the reaction part in the reaction tower and the silicon dissolution part. 8. The silicon manufacturing apparatus according to claim 1, wherein the temperature of the silicon melting part is 1450 ° C. to 1600 ° C. 9. The silicon manufacturing apparatus according to claim 1, wherein the silicon melting portion is heated above the furnace wall from the outside to be equal to or higher than the melting temperature of silicon. 9. The silicon production apparatus according to claim 1, wherein the silicon melting portion heats a heating element placed in the reaction tower by induction heating from outside. 11. The silicon manufacturing apparatus according to claim 1, wherein the silicon holding tank has an external heating mechanism and is held by a melt. 12. The silicon manufacturing apparatus according to claim 1, wherein the silicon holding tank is connected to the outside through a baffle plate so that molten silicon is continuously taken out. 13. The residual reaction gas from which silicon has been separated is lowered below the boiling point temperature of zinc and separated and recovered from the remaining reaction gas as a melt in a cyclone type separation tank. Silicon production equipment The temperature of the zinc separation tank is 750 to 650 ° C. Silicon production apparatus according to claims 1 to 13 The zinc chloride from the zinc separation tank is further cooled and liquefied, and the residual zinc is recovered and led to a zinc gas generation tank. Further, a part of zinc chloride is used as an atmospheric gas in the reaction tower via a gasification step. 15. The silicon manufacturing apparatus according to claim 1, wherein the silicon manufacturing apparatus is supplied.

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