JP2007217262A - Apparatus for manufacturing silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for manufacturing high purity silicon by a zinc reduction of silicon tetrachloride, obtaining high purity silicon by a gas phase reaction in a higher yield, melting in its system, substantially dispensing with the operation for separating other reactant components, and separating and taking out only silicon. <P>SOLUTION: The apparatus is for manufacturing high purity silicon by reducing silicon tetrachloride by zinc in a gas phase, which has a process where zinc gas preheated to a specified temperature is sent to a reaction tower to make a zinc gas atmosphere inside the reaction tower, a process where silicon tetrachloride gas preheated to a specified temperature is supplied into the reaction tower having the zinc gas atmosphere, a process where silicon formed by the reaction in the reaction tower is grown as a solid phase in the reaction gas containing silicon formed by the reaction in the reaction tower, and a process where the solid silicon is separated from the reaction gas. The silicon is taken out as a solid or a melt. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention mainly relates to a silicon manufacturing apparatus and a manufacturing method 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. Has been. 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. There is a problem in that the energy is too large and the manufacturing cost is too high. Furthermore, this process produces a large amount of silicon tetrachloride as a by-product. This silicon tetrachloride has been used for quartz glass raw materials by decomposing with water from the past, but it has become excessive with the increase of silicon production, and the material balance with the problem of yield of crude silicon raw materials Is becoming difficult to remove.

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 (SiHCl ₃ ) as a raw material. On the other hand, Patent Documents 1 and 2 show a method of obtaining high-purity silicon by reacting molten zinc with silicon tetrachloride gas, but in any case, silicon produced in a batch system must be separated from zinc and zinc chloride. In addition, the problem is complicated and impurities are mixed by the separation operation.

The present inventors obtained high-purity silicon by taking out only silicon as a raw material or a by-product in a solid or liquid state by a high-temperature gas phase reaction in which silicon tetrachloride gas is reduced with zinc gas in Patent Document 3. ing. 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 Patent Document 4, Patent Document 5, Patent Document 6, Patent Document 7, Patent Document 8 and the like have been invented, and the purity of silicon is slightly inferior to that of conventional ultra-high purity products. 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 silicon tetrachloride 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 and a silicon production method for obtaining high purity silicon by zinc reduction of silicon tetrachloride, obtaining high purity silicon produced by a gas phase reaction in a higher yield, and further dissolving in the system, An object of the present invention is to provide an apparatus that can substantially separate only silicon and eliminate the separation operation from other reaction components.

The present invention is a silicon production apparatus that obtains high-purity silicon by reducing silicon tetrachloride with zinc in a gas phase, and sends zinc gas that has been adjusted to a predetermined temperature in advance to the reaction tower to create a zinc gas atmosphere in the reaction tower. A step of supplying silicon tetrachloride gas previously adjusted to a predetermined temperature into the reaction tower which is the zinc gas atmosphere, and a reaction gas containing silicon generated by the reaction in the reaction tower; A high-purity silicon production apparatus comprising a step of growing and a step of separating solid phase silicon from a reaction gas, and a silicon production apparatus for obtaining high-purity silicon by reducing silicon tetrachloride with zinc in a gas phase. A process in which zinc gas adjusted to a predetermined temperature in advance is sent to the reaction tower to make the inside of the reaction tower a zinc gas atmosphere, and silicon tetrachloride gas adjusted in advance to a predetermined temperature is reacted in the zinc gas atmosphere. In the reaction gas containing silicon produced by the reaction in the reaction tower, the step of growing the silicon as a solid phase, the step of separating the solid phase silicon from the reaction gas, and heating the separated silicon A high-purity silicon production apparatus having a process of melting and holding in a silicon holding tank, whereby production of high-purity silicon can be performed easily using silicon tetrachloride and zinc as raw materials. Can be obtained as a solid or a melt with very low energy consumption and high yield.

That is, at a high temperature of 1000 ° C. or higher, silicon and zinc chloride are generated almost instantaneously by blowing silicon tetrachloride gas into zinc gas. Silicon can be produced by utilizing this reaction. However, optimization of reaction conditions at this time is extremely important. That is, it is known that this reaction is completed very quickly and almost instantaneously, but the vapor pressure of silicon tetrachloride is extremely high, 200 to 500 times higher than the vapor pressure of zinc or zinc chloride at 1000 ° C. or higher. When silicon tetrachloride is added to the zinc gas, the zinc gas is pushed into the high pressure of the silicon tetrachloride and pushed out unreacted, or if the pressure is kept constant, the volume will change suddenly and the system will lose stability. Or On the other hand, as is often seen in gas phase reactions, the reaction product silicon initially forms very small particles or droplets and then grows, but during this time it also undergoes a very large volume change due to the gas phase reaction. Resulting in a change in pressure.

The present inventors have already proposed a method in which a fibrous silicon crystal is once produced and taken out or melted and taken out as a melt. However, by examining these in more detail, it was found that some silicon could not be collected well due to extremely large pressure or volume fluctuations during the reaction, and the yield was slightly reduced, leading to the present invention. It is a thing. That is, here, for the reaction portion where the pressure change is likely to occur, the temperature is set to a predetermined value in the reaction tower in advance, and silicon tetrachloride gas is blown into the flow of excess zinc gas. This prevents volatilization of zinc gas and reacts instantaneously to zinc chloride gas and silicon, thereby minimizing the influence of the large volume of silicon tetrachloride. By this instantaneous reaction, zinc gas and silicon tetrachloride gas become a flow of zinc gas and zinc chloride gas. The produced silicon grows and stabilizes as crystals in the reaction tower. The gas containing silicon is sent to a swirl type separation device and separated into gas and silicon. By crystallizing silicon once, substantial refining is performed and high purity is achieved. That is, the reaction temperature is 1000 ° C. to 1350 ° C., particularly preferably 1100 to 1250 ° C., and silicon grows in the form of fibrous crystals or needle-like single crystals in the reaction tower maintained at a temperature slightly lower than the reaction temperature. Becomes the main crystal. However, even in this case, since some of the crystals are very small, a portion that cannot be separated from the gas phase may remain, which has led to a decrease in yield in the prior art. For this purpose, the crystal grown in the reaction tower is separated into the gas phase and the silicon crystal by a swirling separator maintained at a temperature higher than the boiling point of zinc and suitable for crystal growth, and concentrated downward. The silicon crystal is taken out as it is, or heat-melted and held in a holding tank. The temperature of the gas / silicon separator is higher than the boiling point of zinc, but it is preferably equal to or lower than the reaction tower temperature, preferably 950 ° C. to 1200 ° C., more preferably 1000 ° C. to 1150 ° C. This further promotes the growth of silicon, improving the yield and reducing possible impurities such as zinc and zinc chloride.

Although the initial wind speed in the swirl separator is not particularly specified, it is preferably about 3 m / second to 5 m / second. The operating power of the slewing separator depends on the volume change of the reaction gas itself, which drops from the gas phase to the liquid phase and finally changes to the liquid phase. This eliminates the need for a blower or the like. The silicon collected under the swirl separator may be taken out as it is, but in order to maintain a stable continuous operation, it is heated and melted and held in a holding tank as a silicon melt, or the silicon melt produced is The body can be continuously taken out through the holding tank. These may be appropriately selected depending on the use and purpose. The heating for melting silicon may be performed by making a heating part independently, but the produced crystal may be dropped into a silicon holding tank to be melted. The melted silicon may be used as a mold as a polycrystalline block, or may be further purified by continuous pulling using this holding tank as a first crucible. These may be appropriately selected depending on the use conditions. The silicon holding tank is preferably a holding tank in which the outside is cooled to keep the wall temperature below the melting point of silicon and the silicon itself is heated and melted by induction heating in order to prevent contamination of the molten silicon. . As a result, silicon can be kept at a higher purity. In addition, a gas deaeration mechanism can be provided in the holding tank.
The temperature of the melted silicon is of course not lower than the melting point of silicon, but is desirably 1500 ° C. or lower, and if it is higher, there is a possibility that a loss due to vaporization of silicon may occur.

As a result, silicon tetrachloride reacts almost 100% and is recovered, so that the separation gas becomes zinc chloride containing unreacted zinc gas. This gas exits the silicon separator and is carried to the zinc separation tank while cooling. Since the boiling point of zinc is 907 ° C. and the boiling point of zinc chloride is 732 ° C., cooling is performed to around the boiling point of zinc chloride, and if necessary, the zinc is separated and recovered in a liquid form by a swirling gas-liquid separator, Zinc is sent again to the zinc vaporization tank and used as a zinc raw material. Zinc may be separated below the boiling point of zinc chloride. In that case, zinc chloride may be recovered from the zinc melting tank as a gas, or a part of the zinc gas is sent to the reaction tower while being mixed with the zinc gas. It may be used as

The remaining zinc chloride gas is further liquefied at a lower temperature and recovered. Ordinarily, it can be sent directly to the zinc chloride electrolytic cell while lowering the temperature. In this case as well, it is of course desirable to be a liquid, but even if zinc chloride gas is included, the influence on electrolysis is negligible. Further, zinc contained slightly in the zinc chloride is also separated in the electrolytic cell and collected together with zinc which is an electrolytic product.

The mixed gas of zinc and zinc chloride after separating the silicon is sent directly to the electrolytic cell while lowering the temperature, where it is lowered and recovered as a zinc chloride-zinc melt, and the zinc chloride can be directly electrolyzed. I can do it. In this case, zinc in the gas falls in the zinc chloride electrolyte, and returns to the reaction step as a zinc raw material together with zinc generated by electrolysis.
It is also possible to collect zinc in advance and send zinc chloride containing a small amount of the remaining zinc directly to the electrolytic cell and recover it as a zinc gas raw material.

According to the present invention, high purity silicon can be obtained in a high yield by using silicon tetrachloride as a raw material, which can be obtained very easily as a raw material, or has conventionally been a problem in handling as a by-product. In addition, the reaction itself is simple, and the reaction rate is extremely fast, so that it is possible to use a small facility. At the same time, it has a substantial refining effect by crystallization once in the process, so it can be highly purified. Moreover, by using the product silicon as a melt, there is an effect that continuous operation is possible.

An embodiment of the present invention will be described with reference to the drawings. That is, FIG. 1 corresponds to claim 1 of the present invention, and FIG. 2 corresponds to claim 2.

In FIG. 1, the raw material zinc is charged into the zinc dissolution tank 3 from 1 to generate molten zinc, converted into zinc vapor in the zinc vaporization tank 4, and heated to about 1200 ° C. as the reaction temperature by the heating device 6. It feeds into the reaction tower 8. In addition, it is desirable that the zinc gas is swirling in the reaction tower, thereby increasing the reaction area and enabling a fast reaction. On the other hand, the liquid silicon tetrachloride 2 is vaporized in the evaporation tank 5 to become a gas, and is heated to about 1200 ° C., which is the reaction temperature, by the heating device 7. It is blown so as to turn in the same direction as the swirling flow.

When the pressure of silicon tetrachloride gas is the same, it is extremely large. Therefore, a plurality of blowing ports are provided so that the reaction can be instantaneously mixed with the zinc gas, and the swirling flow is created to increase the contact with the zinc gas. As a result, the silicon tetrachloride gas instantaneously reacts with the zinc gas to form silicon and zinc chloride gas, and the presence of silicon tetrachloride does not substantially occur in the reaction tower. The turbulence disappears and the gas moves to zinc chloride gas, which has almost twice the volume due to the vapor pressure. However, silicon tetrachloride having an extremely large volume must be continuously and constantly supplied to the reaction tower. The portion after the reaction portion of the reaction tower is the growth portion of the silicon crystal, and is maintained at a temperature slightly lower than the reaction temperature. If the gas flow in the reaction tower also draws a swirl flow, the generated silicon gathers at the center of the gas flow, resulting in a smoother gas flow and the influence of the reaction tower wall on the generated silicon can be minimized. Thus, the silicon produced by the swirling flow in the reaction tower is collected at the center of the flow and is sent to the next swirling silicon separation tank 9 while growing as a solid. The reaction tower temperature is maintained at 950 to 1200 ° C., which is slightly lower than the reaction temperature.

Further, a mixed gas composed of silicon, zinc which is an atmospheric gas, and zinc chloride which is a reaction by-product gas moves to the swivel-type silicon separator 9. The gas inflow speed at this time is about 1 to 10 m / sec, and usually about 3-5 m / sec. Here, the gas moves from the top to the zinc separator 10 while drawing a swirling flow. Also, the silicon collects in the central portion and moves downward and is recovered as silicon 13 while minimizing contact with the furnace wall by the swirling principle.

The temperature of the zinc separator 10 is 650 ° C. to 700 ° C., and the separated zinc is sent to the zinc dissolution tank 3. The zinc chloride excluding zinc is further cooled and collected in the zinc chloride fusion section 11, electrolyzed in the electrolytic bath 12, divided into zinc 1 and chlorine gas 14, and zinc is sent to the zinc dissolution bath 3. In this way, high purity silicon is continuously produced while zinc is recycled in the system. In addition, the zinc separation part 10 and / or the zinc chloride fusion | melting part 11 can serve as an electrolytic cell. The electrolysis temperature is not particularly specified but is 500 to 550 ° C.

In addition to these, in FIG. 2, a silicon melt tank 15 is provided in the silicon take-out part of the silicon separator 9, and the accumulated silicon is heated and melted to be held in the melt silicon holding tank 16, and continuously melted. It is something to be taken out as. It is also possible to directly attach a crystal growth device or a casting device to this. Here, the silicon melt tank 15 can also serve as the melt silicon holding tank 16.

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 produced | generated silicon | silicone is taken out as a melt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Zinc 2 Silicon tetrachloride 3 Zinc melting tank 4 Zinc vaporization tank 5 Silicon tetrachloride vaporization tank 6 Zinc gas heating temperature adjustment apparatus 7 Silicon tetrachloride gas heating temperature adjustment apparatus 8 Reaction tower 9 Silicon separation tank 10 Zinc separation part 11 Zinc chloride Molten part 12 Zinc chloride electrolytic cell 13 Generated silicon 14 Chlorine 15 Silicon melted cell 16 Molten silicon holding tank

Claims (13)

A silicon production apparatus that obtains high-purity silicon by reducing silicon tetrachloride with zinc in a gas phase, and sending zinc gas adjusted to a predetermined temperature in advance to the reaction tower to form a zinc gas atmosphere in the reaction tower; A step of supplying silicon tetrachloride gas, which has been adjusted to a predetermined temperature in advance, into the reaction tower which is the zinc gas atmosphere, and a step of growing the silicon as a solid phase in a reaction gas containing silicon generated by the reaction in the reaction tower. And a process for separating solid phase silicon from a reaction gas. A silicon production apparatus that obtains high-purity silicon by reducing silicon tetrachloride with zinc in a gas phase, and sending zinc gas adjusted to a predetermined temperature in advance to the reaction tower to form a zinc gas atmosphere in the reaction tower; A step of supplying silicon tetrachloride gas, which has been adjusted to a predetermined temperature in advance, into the reaction tower which is the zinc gas atmosphere, and a step of growing the silicon as a solid phase in a reaction gas containing silicon generated by the reaction in the reaction tower. And a process for separating solid phase silicon from a reaction gas, and a process for heating and melting the separated silicon and holding it in a silicon holding tank. The high purity silicon production apparatus according to claim 1 or 2, wherein the zinc gas is a mixed gas of zinc gas and zinc chloride gas. The high-purity silicon production apparatus according to claim 1 or 2, wherein the predetermined temperature of the zinc gas is 1000 to 1350 ° C. The high-purity silicon production apparatus according to claim 1 or 2, wherein the predetermined temperature of the silicon tetrachloride gas is 1350 ° C or lower and is the same as or lower than that of the zinc gas. 3. The high-purity silicon production apparatus according to claim 1, wherein the temperature of the reaction tower is 950 ° C. to 1200 ° C., and also serves as a step of growing silicon as solid phase silicon. The high-purity silicon production apparatus according to claim 1 or 2, wherein the gas phase and the solid phase silicon phase are separated by a swivel type separation device. The high-purity silicon production apparatus according to claim 1 or 2, wherein the temperature of the rotary separator is 950 ° C or higher and is equal to or lower than the reaction temperature. 3. The high purity silicon according to claim 2, wherein the silicon holding tank is heated by high frequency induction and the holding tank itself is cooled so that the wall of the holding tank and the melted silicon are not in direct contact with each other. Manufacturing equipment. 3. The apparatus for producing high-purity silicon according to claim 2, wherein the silicon is heated and melted in a silicon holding tank. 3. The high purity silicon production apparatus according to claim 1, wherein unreacted zinc is separated from the reaction gas in a liquid state and recycled as a zinc gas raw material. The high-purity silicon production apparatus according to claim 1, 2 and 11, wherein unreacted zinc is separated from the reaction gas by a swirl type separation apparatus. 12. The high-purity silicon production apparatus according to claim 1, wherein the reaction gas is sent to an electrolysis device, unreacted zinc and zinc produced by electrolysis are taken out in a liquid state and recycled as a zinc gas raw material.

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