JP2013086995A - Method and apparatus for producing silicon, silicon wafer and panel for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon production method capable of surely bringing a treating agent into contact with molten silicon in the case of removing impurities in molten silicon with the treating agent, thereby efficiently contributing to the reaction with impurities.SOLUTION: The silicon production method comprises a pushing step of pushing the treating agent into the system at a level lower than the liquid level of the molten silicon in the system and a removal step of reacting the impurities in the molten silicon with the treating agent and removing the impurities from the system.

Description

  The present invention relates to a method for producing silicon used as a material for producing a solar cell panel, for example.

  In general, high-purity metallic silicon having a specific resistance value of 0.5 to 1.5 Ω · cm or more and a purity of 99.9999% (6N) or more is used for the polysilicon solar cell. The high-purity metal silicon is most preferable as an industrial method, since the raw material unit price is low, and the impurities are purified and removed from the source metal silicon containing a relatively large amount of impurities.

Of the impurities contained in the raw metal silicon, iron, aluminum, titanium and calcium are removed to the silicon liquid phase side by solidifying and segregating molten silicon (silicon obtained by melting the raw metal silicon containing impurities). Can do. Calcium and the like can be removed by evaporating molten silicon in a vacuum of about 1.3 × 10 ^{−2 to} 1.3 × 10 ⁻⁴ Pa (10 ⁻⁴ to 10 ⁻⁶ Torr). it can.

  However, among impurities, boron and phosphorus are very difficult to remove, and in particular, boron is difficult to remove. For example, in molten silicon, oxygen or carbon dioxide, or water vapor is added to inert argon and blown into the silicon to be gasified and removed as a compound of boron, oxygen, or hydrogen. (See Patent Document 1 and Patent Document 2).

  In the above-described method, it takes time to oxidize boron (B) in the raw metal silicon using water vapor or the like and remove it as BO gas. At the same time, silicon is also oxidized, resulting in a large loss. In particular, when water vapor is blown into molten silicon, a large amount of hydrogen is generated as a side reaction, which causes a safety problem.

  In addition, as a silicon purification method using alkali halide, slag (slag mainly composed of silicon dioxide in raw metal silicon) is made from raw metal silicon sludge, and this is used for component adjustment when removing impurities Thus, a technique for recovering silicon (see Patent Document 3) has been proposed, but satisfactory purity silicon has not necessarily been obtained. Further, since the slag is an oxide, usable containers are limited to oxide refractory materials such as silica and alumina, and there is a problem that the apparatus becomes expensive. Further, in induction heating, it is necessary to heat a graphite rod or the like in a container until the silicon is melted, and the process may be complicated. Furthermore, the slag method requires a separation process of molten slag from silicon, and there is a problem that the process is complicated in this respect as well.

  In Patent Document 4, 20 g of raw material metal silicon powder is pulverized, mixed with NaF having the same particle size at a mass ratio of 1: 1, and heated at 1300 ° C. to melt solid silicon with NaF. Contacting, second sample heated at 1450 ° C. for 10 minutes to melt NaF and raw metal silicon, cooling these samples (NaF and silicon) to room temperature, aqueous elution and subsequent decantation And the process of separating silicon from NaF in each sample by filtering.

  However, in the method described in Patent Document 4, the silicon is merely purified by separating the silicon from the solid material containing NaF and raw metal silicon using filtration or the like, and the purification effect is not sufficient. In addition, there is a problem that the work of separating silicon is not easy. Further, near the melting point of silicon (Si), the vapor pressure of NaF is high, and there is a problem that NaF evaporates while heating a mixture of Si and NaF to raise the temperature.

  As a means for solving the above problem, the applicant has disclosed Patent Document 5. That is, impurities contained in molten silicon are obtained by bringing molten silicon containing impurities into contact with a salt such as NaF in a container, reacting the impurities and salt in the molten silicon, and removing the impurities out of the system. Can be efficiently removed.

Japanese Patent Laid-Open No. 11-49510 JP-A-4-228414 U.S. Pat.No. 4,388,286 JP-A-62-502319 International Publication No. 2011/001919 Pamphlet

  Here, in the technique according to Patent Document 5, for example, salt powder is put into molten silicon in a container, and the molten silicon and salt are brought into contact with each other to cause impurities to react with the salt. As a result, the impurities reacted with the salt are discharged out of the system. However, when salt powder is put into a container, the powder may scatter in the system, or melt and evaporate due to heat in the system, and the salt may be discharged out of the system without contacting the molten silicon. It was.

  The present invention has been made in view of the above problems, and when removing impurities in molten silicon using a treatment agent, the treatment agent can be reliably brought into contact with the molten silicon, and the reaction with impurities is efficient. It is an object of the present invention to provide a method for manufacturing silicon, which can contribute to the above.

  As a result of various studies to solve the above problems, the present inventors have introduced the treatment agent into the molten silicon by pouring the treatment agent below the liquid surface after the treatment agent has been introduced into the liquid surface of the molten silicon. It has been found that it can be used without waste by making sure that it is in contact with. In particular, the bulk treatment agent is poured into the molten silicon liquid surface and the bulk treatment agent is pushed in, or the bulk treatment agent is fixed to the rod-like body, and the rod-like body is pushed in to treat the treatment agent with the molten silicon liquid. It has been found that in the form of pushing down the surface, it is possible to more appropriately prevent the treatment agent from being scattered and the like, and the treatment agent can be used without waste. The present invention has been accomplished based on the findings.

That is, the gist of the present invention resides in the following (1) to (13).
(1) A treatment step for pushing a treatment agent below the liquid level of molten silicon in the system, a removal step for reacting impurities in the molten silicon with the treatment agent, and removing the impurities out of the system. A method for producing silicon.
(2) The treatment agent is in a lump shape, and in the indentation step, the treatment agent and the molten silicon are brought into contact with each other by introducing the lump treatment agent into the liquid surface of the molten silicon, and the treatment agent is indented. The method for producing silicon according to (1), wherein the means is used to push down below the liquid level of the molten silicon.
(3) The treatment agent is in a lump shape, the treatment agent is brought into contact with the molten silicon by fixing the massive treatment agent to the rod-like body and inserting the rod-like body into the system. The method for producing silicon according to (1), wherein the silicon surface is pushed downward from the liquid surface.
(4) The method for producing silicon according to any one of (1) to (3), wherein the impurities include boron.
(5) The method for producing silicon according to any one of (1) to (4), wherein the treating agent is a salt.
(6) The treating agent is a salt of an alkali metal and a halogen, a salt of an alkaline earth metal and a halogen, a composite salt containing an alkali metal and a halogen, and a composite salt containing an alkaline earth metal and a halogen, The method for producing silicon according to any one of (1) to (5), comprising at least one compound selected from the group consisting of:
(7) The treating agent is lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF), cesium fluoride (CsF), sodium silicofluoride (Na _2). SiF ₆ ), cryolite (Na ₃ AlF ₆ ), a mixture of sodium fluoride and barium fluoride, a mixture of sodium fluoride, barium fluoride and barium chloride, and a mixture thereof. The method for producing silicon according to any one of (1) to (6), comprising at least one selected compound.
(8) The method for producing silicon according to any one of (1) to (7), wherein an amount of the treatment agent is 5% by mass or more and 300% by mass or less with respect to the molten silicon.
(9) A silicon manufacturing apparatus that contacts molten silicon containing impurities and a treatment agent in the system, reacts the impurities in the molten silicon with the treatment agent, and removes the impurities out of the system. In the system, there are a bottom part, a side part and an upper opening part, a container filled with molten silicon containing the impurities, a pushing means for pushing the treatment agent below the liquid level of the molten silicon, A silicon manufacturing apparatus, comprising: a heating unit that heats the molten silicon containing the impurity and the treatment agent; and a removal unit that removes evaporated material from the molten silicon and the treatment agent to the outside of the system.
(10) The silicon manufacturing apparatus according to (9), wherein the pushing means pushes a blocky treatment agent present on the liquid surface of the molten silicon downwardly of the liquid surface.
(11) The silicon manufacturing apparatus according to (9), wherein the pushing means is a rod-like body capable of fixing a massive treatment agent at a tip.
(12) A silicon wafer using silicon obtained by the method for producing silicon according to any one of (1) to (8).
(13) A solar cell panel using silicon obtained by the method for producing silicon according to any one of (1) to (8).

  In the present invention, “in the system” means a reaction between molten silicon and a treatment agent, evaporation of impurities due to reaction with the treatment agent, and evaporation of the treatment agent. For example, when a heating means or container is housed in a housing with a discharge port, silicon is purified inside the housing, and impurities are removed by evaporation through the discharge port, the inside of the housing is regarded as the system. be able to. On the other hand, “outside the system” refers to a place where the recovery of impurities removed from the molten silicon and the recovery / purification of the evaporation product of the processing agent are performed. For example, the outside of the housing can be regarded as outside the system. The “treatment agent” means a substance that melts when added to molten silicon and can react with impurities contained in the molten silicon. However, when added to molten silicon, at least a part of the treatment agent may be decomposed and vaporized.

In the present invention, the shape of the “bulk treatment agent” is not particularly limited, and examples thereof include a cube, a rectangular parallelepiped, a spherical body, and a rod-like body. The size of the bulk processing agent is not particularly limited as long as it can be charged into the system and does not interfere with the processing agent. More specifically, the longest side of the treating agent or the lower limit of the longest diameter is usually 1 mm or more, preferably 2 mm or more, more preferably 5 mm or more, and most preferably 10 mm or more. The upper limit of the longest side or the longest diameter of the treatment agent is not particularly limited, and is preferably 200 cm or less, more preferably 100 cm or less, further preferably 50 cm or less, particularly preferably 20 cm or less, and most preferably The treatment agent which is 10 cm or less is said.
In the “bulk treatment agent”, the treatment agent may densely form a lump, or may aggregate to form a lump with voids. For example, a dense block treatment agent can be obtained by melting and solidifying the treatment agent. In addition, by heating and sintering a powdery processing agent or a granular processing agent, an agglomerated processing agent having voids can be obtained. Or the block treatment agent obtained by various shaping | molding methods, such as pressure molding, may be sufficient.

  According to the present invention, by bringing molten silicon containing impurities such as boron (B), aluminum (Al) and calcium (Ca) into contact with the processing agent in the system, the silicon liquid phase and the processing agent liquid are brought into contact with each other. An interface with the phase can be formed, and the impurity can be efficiently removed by reacting the impurity in the silicon with the treatment agent via the interface. That is, according to the present invention, it is possible to provide a silicon manufacturing method capable of efficiently removing impurities contained in molten silicon in the same process in a short time to obtain high-purity metal silicon.

  On the other hand, by reacting impurities in the silicon with the treatment agent via the interface, a part of the reaction product generated by the reaction is evaporated and removed as a compound having a high vapor pressure, and a part thereof is dissolved in the treatment agent. Here, in the present invention, the treating agent is pushed below the liquid level of the molten silicon. Thereby, the processing agent which evaporates without contacting molten silicon can be reduced, and the processing agent can be contributed to the reaction without waste. That is, according to the present invention, when removing impurities in the molten silicon using the treatment agent, the treatment agent can be reliably brought into contact with the molten silicon, and can efficiently contribute to the reaction with the impurities. In addition, a method for manufacturing silicon can be provided.

It is a figure for demonstrating the whole flow about the manufacturing method of silicon. It is a figure for demonstrating collection | recovery of a processing agent. It is a figure which shows a pushing means roughly. It is a figure for demonstrating an example of the manufacturing apparatus of silicon. It is a figure for demonstrating an example of the manufacturing apparatus of silicon. It is a figure for demonstrating an example of the manufacturing apparatus of silicon. It is a figure for demonstrating an example of the manufacturing apparatus of silicon.

  DESCRIPTION OF EMBODIMENTS Embodiments of the present invention will be described in detail below. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention. It is not limited to the contents.

1. Silicon manufacturing method The silicon manufacturing method according to the present invention is a process for injecting a treatment agent below the liquid level of molten silicon in the system, reacting an impurity in the molten silicon with the treatment agent, and removing impurities. It is characterized by having a removal step of removing it outside the system.

  FIG. 1 shows an example of a silicon manufacturing method (manufacturing method S100) according to the present invention. As shown in FIG. 1, the manufacturing method S100 includes a step of introducing silicon into the system (step S1), a step of melting the injected silicon (step S2), a treatment agent being added to the molten silicon, and a molten silicon liquid. A step of pushing the processing agent below the surface (step S3), a step of reacting the molten silicon and the processing agent in a closed system (step S4), a step of replacing the closing means (step S5), and a state where the closing means is removed The step of reacting the molten silicon and the processing agent in an open system to remove the processing agent and impurities out of the system (step S6) and the step of solidifying the molten silicon in the system (step S7). . In addition, as shown in FIG. 1, in manufacturing method S100, after process S5, it returns to process S3 and repeats process S3-S5. Hereinafter, it demonstrates for every process.

1.1. Process S1
Step S1 is a step of introducing metal silicon as a raw material into the system. The source metal silicon contains at least boron (B) as an impurity, and, for example, phosphorus (P), iron (Fe), aluminum (Al), calcium (Ca), titanium (Ti), etc. It may be included. In the present invention, among these impurities, boron (B) can be removed, and aluminum (Al) and calcium (Ca) can be suitably removed.

  The total concentration of impurities in the raw metal silicon is preferably 10 to 500 ppm, more preferably 10 to 300 ppm, based on mass. The raw material metal silicon in such a concentration range is preferable because it can be easily obtained by arc carbon reduction or the like and the cost can be kept low. Further, as raw metal silicon, silicon cutting scraps, silicon from which silicon carbide has been removed by carbon reduction, or the like may be used.

1.2. Process S2
Step S2 is a step of heating and melting silicon charged into the system. The silicon may be heated using a known heating means. The heating temperature is preferably at least the melting point of silicon (1410 ° C.), more preferably at least 1450 ° C. In addition, the upper limit of the temperature is preferably 2000 ° C. or less and more preferably 1700 ° C. or less so that the evaporation rate of the treatment agent is moderately suppressed and impurities are effectively removed.

1.3. Process S3
Step S3 is a step of adding the processing agent to the molten silicon and pushing the processing agent below the liquid level of the molten silicon. The processing agent is melted at the melting temperature of the raw material metal silicon, and constitutes an interface between the silicon liquid phase and the processing agent liquid phase, so that impurities in the molten silicon, particularly boron (B), aluminum (Al), calcium The substance is not particularly limited as long as it is a substance capable of reacting with impurities such as (Ca) and evaporating the impurities into the gas phase, or a substance capable of dissolving the impurities in the treatment agent itself and evaporating together with the impurities. In view of the above, it is preferably a salt.
More preferably, the treating agent is a salt of an alkali metal and a halogen, a salt of an alkaline earth metal and a halogen, a composite salt containing an alkali metal and a halogen, and a composite salt containing an alkaline earth metal and a halogen. It contains at least one compound selected from the group consisting of: In particular, lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF), cesium fluoride (CsF), sodium silicofluoride (Na ₂ SiF ₆ ), cryolite (Na ₃ AlF ₆ ), a mixture of sodium fluoride and barium fluoride, and a mixture of sodium fluoride, barium fluoride and barium chloride, or a mixture thereof, at least one kind selected from the group consisting of It is preferable to include a compound. Among these, from the viewpoint of suppressing a large amount of the treatment agent component from being taken into silicon and being able to be easily purified even when it is taken in, the alkali metal and / or alkaline earth metal fluoride is used. Are preferred, alkali metal fluorides are more preferred, and NaF is particularly preferred. In this case, it may be a complex salt or a mixed salt with other salts. In addition, when raw material metal silicon is dissolved, an oxide film may be formed. However, in the present invention, the oxide can be dissolved in the treatment agent described above. Moreover, if it is an above-described processing agent, a normal graphite can be used as a container holding a processing agent, and it is preferable also from an economical viewpoint. In addition, the processing agent can also use the thing which mixed processing agents beforehand as needed, cooled after heat-melting, and made into flux.

  In addition, when forming the liquid phase of a processing agent on the liquid phase of a molten silicon, it is good to use a processing agent with a smaller density than silicon (Si). Examples of the treating agent include alkali metal fluoride salts having an atomic number smaller than that of Cs.

  Although it is desirable that the content of impurities in the treatment agent is low, even if the treatment agent contains impurities, the impurities are often fluorinated, and most of them are evaporated at the treatment temperature. Because there is no problem. Therefore, it is possible to use a normal industrial chemical as the treating agent. However, in the present invention, it is possible to remove impurities in the treatment agent by heating, and to obtain a predetermined bulk treatment agent by sintering or cooling and solidifying after melting. it can.

  The amount of the treating agent used is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, and particularly preferably 30% by mass or more with respect to the raw material metal silicon (molten silicon). Moreover, 300 mass% or less is preferable, less than 100 mass% is more preferable, 70 mass% or less is more preferable, and 50 mass% or less is especially preferable. A sufficient purification effect can be obtained by setting the amount of the treatment agent used to 5% by mass or more. In the present invention, as will be described later, first, the molten silicon and the treatment agent are sufficiently reacted in a closed system, whereby the amount of the treatment agent used can be reduced.

Examples of the form in which the treatment agent is added to the molten silicon and the treatment agent is pushed below the liquid level of the molten silicon include the following forms.
(A) A mode (B) in which a treating agent and molten silicon are brought into contact with each other by introducing a lump-like treating agent into the molten silicon liquid surface and the treating agent is pushed below the molten silicon liquid surface by using a pushing means. A configuration in which the treatment agent is brought into contact with the molten silicon and pushed down below the liquid level of the molten silicon by fixing the massive treatment agent to the rod-like body and inserting the rod-like body into the system.

  In the present invention, the shape of the “bulk treatment agent” is not particularly limited, and various shapes such as a cube, a rectangular parallelepiped, a spherical body, or a rod-like body can be exemplified. The size of the bulk processing agent is not particularly limited as long as it can be put into the molten silicon in the system and does not interfere with the processing agent. More specifically, the longest side of the treating agent or the lower limit of the longest diameter is usually 1 mm or more, preferably 2 mm or more, more preferably 5 mm or more, and most preferably 10 mm or more. The upper limit of the longest side or the longest diameter of the treatment agent is not particularly limited. For example, it is preferably 200 cm or less, more preferably 100 cm or less, still more preferably 50 cm or less, particularly preferably 20 cm or less, The treatment agent is preferably 10 cm or less. In the “bulk treatment agent”, the treatment agent may densely form a lump, or may aggregate to form a lump with voids. For example, a dense block treatment agent can be obtained by melting and solidifying the treatment agent. Further, by heating and aggregating (sintering) a powdery processing agent or a granular processing agent, an agglomerated processing agent having voids can be obtained. Or the block treatment agent obtained by various shaping | molding methods, such as pressure molding, may be sufficient.

  As the “bulk treatment agent” in the form of (A), for example, a treatment agent having a diameter larger than the gas escape hole provided in the “pushing means” and smaller than the inner diameter of the “pushing means” is preferable. . More specifically, the lower limit of the longest side or the longest diameter is preferably 2 mm or more, more preferably 5 mm or more, most preferably 10 mm or more, and the upper limit is preferably 100 cm or less. The form of the “pushing means” is not particularly limited as long as the treatment agent on the liquid level of the molten silicon can be pushed down below the liquid level. A specific form will be described later.

  Alternatively, as the “bulk treatment agent” in the form of (B), it is sufficient that it can be appropriately fixed to the “rod-like body” and can be inserted into the system, and the longest side or the lower limit of the longest diameter is preferable. Is 10 mm or more, more preferably 30 mm or more, most preferably 50 mm or more, and the upper limit is preferably 200 cm or less. In particular, a substantially cylindrical treatment agent having a diameter of 10 to 1000 mm and a height of 50 to 2000 mm can be suitably used. The “rod-shaped body” is particularly in a form as long as a lump treatment agent can be inserted into the system and the lump treatment agent can be pushed below the liquid level of the molten silicon. It is not limited. A specific form will be described later.

  The temperature at which the raw metal silicon and the treatment agent are heated and melted may be equal to the temperature at which the silicon is melted. That is, the melting point of silicon (1410 ° C.) or higher is preferable, and 1450 ° C. or higher is more preferable. The upper limit of the temperature is preferably 2000 ° C. or lower, and more preferably 1700 ° C. or lower.

  Thus, an interface between the silicon liquid phase and the processing agent liquid phase can be formed by bringing the molten silicon into contact with the processing agent. Here, in the present invention, the processing agent is pushed below the liquid level of the molten silicon, the processing agent that evaporates without contacting the molten silicon can be reduced, and the processing agent can be reacted without waste. Can contribute. In steps S4 to S6 described later, impurities in the molten silicon and the treatment agent can be reacted via the interface between the silicon liquid phase and the treatment agent liquid phase, and the impurities are evaporated or treated in the gas phase. Can be transferred to the agent. Further, through the interface between the silicon liquid phase and the processing agent liquid phase, the gas in which the processing agent has evaporated or the decomposition product gas formed by partial decomposition of the composite compound is allowed to act on the silicon, so that The impurities can be reacted with the treating agent.

1.4. Step S4
Step S4 is a step of reacting the molten silicon and the processing agent in a closed system. In order to make the reaction system a closed system, for example, molten silicon and a processing agent may be filled in a container such as a crucible and the container may be closed by a closing means such as a lid. The reaction treatment time, that is, the contact time between the molten silicon and the treatment agent is usually preferably 0.1 hours or more, more preferably 0.25 hours or more, and particularly preferably 0.5 hours or more. Moreover, 12 hours or less are preferable normally, 6 hours or less are more preferable, and 2 hours or less are especially preferable. The longer the reaction treatment time, the more effective the reduction of impurities, but a shorter one is desirable from the viewpoint of process cost.

As described above, the compound containing impurities generated at the interface between the molten silicon and the treatment agent, that is, the reaction product obtained by reacting the impurities in the silicon with the treatment agent evaporates or partially dissolves in the treatment agent. Evaporates with. Here, since the processing agent is pushed below the liquid level of the molten silicon, most of the processing agent can contribute to the reaction without waste, but some of them react with impurities in the molten silicon. Evaporate without However, in step S4, since the reaction system is a closed system, the evaporated treatment agent can condense in the system, and can drop and reach the liquid level of the molten silicon again. That is, in step S4, the evaporated material from the molten silicon liquid surface is condensed in the reaction system to form a condensed material, and then the condensed material is dropped into the molten silicon and used again as a processing agent. The interface between silicon and the treatment agent is always properly formed. Thus, by circulating the processing agent in the reaction system, the processing agent can contribute to the reaction without waste, and the loss of the processing agent can be suppressed.
However, in step S4, circulation reuse by dropping the treatment agent is not essential. It is possible to collect the processing agent condensed in the closing means in step S5 described later without dropping the processing agent.

In step S4, the boundary layer functioning as a reaction field formed in the vicinity of the interface between the silicon liquid phase and the processing agent liquid phase is made relatively thin by creating a flow having a large relative velocity between the molten silicon and the processing agent. be able to. For example, a flow having a large relative speed can be created by heating by electromagnetic induction stirring. By doing in this way, reaction with an impurity and a processing agent can be accelerated further. Alternatively, the reaction between the impurity and the treating agent can be further promoted by the methods according to the following (i) to (iv).
(I) A method of blowing an inert gas into the silicon liquid phase.
(Ii) A method of induction stirring the silicon liquid phase using a high frequency induction furnace.
(Iii) A method of mechanically pushing the treatment agent floating on the upper layer into the lower silicon layer. Alternatively, a method of mechanically pushing up the treatment agent sinking to the lower layer to the upper silicon layer. Mechanically pushing in or pushing up means pushing the upper treatment agent into the lower silicon layer using mechanical means, for example, a concave jig made of graphite, or pushing the lower treatment agent into the upper silicon. Say.
(Iv) A method of stirring the liquid phase using a rotor.

1.5. Process S5
Step S5 is a step of replacing the closing means. In the above-described step S4, the impurities in the molten silicon react with the treatment agent to evaporate. Here, as described above, the evaporated treatment agent is preferably allowed to react with impurities in the molten silicon by being adhered to the closing means, condensed, and dropped again into the molten silicon. In step S4, such a cyclic reaction is repeated, so that impurities are concentrated over time in the treatment agent that has adhered to the closing means and condensed. At this time, the closing agent may be preferentially condensed to the predetermined portion by controlling the predetermined portion to a low temperature using, for example, cooling water. In step S5, in order to remove the condensate of the processing agent containing impurities thus concentrated from the closing means, the closing means is replaced with a new closing means.

  After replacing the closing means in step S5, as indicated by the arrow in FIG. 1, the processing agent is added again to the system (step S3), and the reaction is performed in the closed system using the new closing means. (Step S4), the closing means is replaced again (Step S5). After repeating steps S3 to S5 in this way, the closing means is removed and the process proceeds to step S6. About repetition of process S3-S5, the frequency | count of the repetition is not specifically limited, What is necessary is just to determine suitably, considering the quantity and processing time of the added processing agent.

1.6. Step S6
In step S6, after removing the closing means after step S4, the molten silicon and the processing agent are reacted in an open system while arbitrarily adding and pushing in the processing agent again to the molten silicon, and the processing agent and impurities. Is a step of removing the outside of the system. As described above, the compound containing impurities generated at the interface between the molten silicon and the treatment agent, that is, the reaction product obtained by reacting the impurities in the silicon with the treatment agent evaporates or partially dissolves in the treatment agent. And can be removed by evaporation. That is, by making the reaction system an open system, impurities can be easily removed out of the system together with the treatment agent.

The pressure (decompression degree) at the time of evaporation removal in step S6 is sufficient if it is atmospheric pressure, but it is preferable to reduce the pressure to about 10 ⁻⁴ Pa in some cases. In addition, it is preferable to blow an inert gas such as argon into the molten silicon at the time of evaporative removal because evaporative removal is promoted. Moreover, it is preferable to stir molten silicon using various means like process S4.

  After evaporating and removing the impurities together with the treatment agent, it is also preferable to remove the remaining treatment agent and other impurities (phosphorus etc.) contained in the molten silicon by evacuating the inside of the container, if necessary.

  The reaction between the impurities contained in the molten silicon and the treatment agent will be described in more detail including its action and the like.

(A) When using sodium fluoride (NaF) as a treating agent The specific gravity of sodium fluoride (NaF) at 1500 ° C. is about 1.8, which is lighter than the specific gravity of silicon (about 2.6). Therefore, in the system, an interface between the lower silicon liquid phase and the upper NaF liquid phase is formed.

In such a case, it is considered that the following reaction occurs through the interface, and boron (B), which is an impurity in the molten silicon, evaporates as a reactant into the gas phase, and part of the boron is dissolved in the treatment agent. Moving.
4NaF + B = 3Na + NaBF ₄ or 3NaF + B = 3Na + BF ₃

Further, it is considered that the following reaction occurs with respect to aluminum (Al) which is an impurity in molten silicon. Unlike boron, the vapor pressure of the product is low, so in this case it dissolves in the treatment agent, but is removed together when the treatment agent is evaporated off.
Al + 6NaF = Na ₃ AlF ₆ + 3Na

  On the other hand, a part of Na in NaF is taken into molten silicon, but this can be easily removed by alkali removal treatment.

NaBF ₄ and BF _3, etc., which are likely to first dissolved NaF, vapor pressure is high, the majority during the process evaporates. Even if the impurities remain dissolved in NaF, the impurities can be removed together with NaF by raising the temperature in step S6 or evaporating in a reduced pressure state.

Aluminum (Al) and calcium (Ca) are also removed from the molten silicon in the same process. Aluminum (Al) and calcium (Ca) react with NaF to form Na ₃ AlF ₆ and NaCaF ₅ respectively, dissolve in the treatment agent, and are removed in the process of removing the treatment agent.

NaF and Si may react to produce SiF ₄ , and gaseous SiF ₄ may react with impurities, but in any case, the impurities are fluorides with high vapor pressure. Can be removed.

(B) can also be used complex compounds NaF and SiF ₄ as the treating agent complex compounds NaF and SiF ₄ as if treatment agent used _{(Na 2 SiF 6) (Na} 2 SiF 6). In this case, Na ₂ SiF ₆ partially decomposes before becoming a liquid phase, and becomes NaF and SiF ₄ .

Since SiF ₄ is a gas, it is convenient to push Na ₂ SiF ₆ mechanically into the molten silicon because the gas reacts with impurities in the melt. Further, since the reaction between NaF and liquid phase silicon (Si) is suppressed, there is an advantage that the yield of silicon to be purified is improved.

These reactions are usually preferably carried out at 0.5 to 2 atmospheres, and atmospheric pressure sealed with an inert gas such as argon is economically desirable. Even at atmospheric pressure, the treatment agent can be almost evaporated. Furthermore, when removing completely, it is preferable to evaporate by making a vacuum of about 1.3 × 10 ^{2 to} 1.3 × 10 ⁻³ Pa (1 to 10 ⁻⁵ Torr). By doing so, the melt is only silicon, and can be easily recovered by casting into a mold in step S7 described later.

  In Steps S4 to S6, when oxygen is present in the system, the oxygen and molten silicon react to generate an oxide (particularly silica). Silica exists in a solid state at the interface between the molten silicon and the treatment agent, and may reduce the contact interface between the treatment agent and the molten silicon. That is, the production of silica hinders the reaction between the impurities and the treating agent, and there is a possibility that the impurities cannot be removed efficiently. In the above description, the oxide is described as being dissolved in the treating agent. However, the formation of silica may be prevented by providing the following steps.

  That is, it has a step of removing oxygen from the system to the outside by circulating a gas that does not contain oxygen in the system, and the molten silicon containing impurities and the treatment agent are brought into contact with each other in the system, and the molten By producing a silicon production method that includes a step of reacting impurities in the silicon with a treatment agent and removing the impurities out of the system, oxygen in the system is removed, resulting in generation of silica. Can be suppressed.

  In this case, a gas containing no oxygen may be circulated in the system by blowing a gas containing no oxygen into the liquid phase of the molten silicon. As a result, oxygen in the molten silicon can also be driven out of the system, and generation of silica can be further suppressed.

  Argon gas is preferable as the gas not containing oxygen.

  In addition, when a gas containing no oxygen is circulated in the system, the gas can be used as a carrier gas. That is, impurities removed by evaporation from molten silicon can be removed out of the system using a gas that does not contain oxygen as a carrier gas. Thereby, oxygen removal and impurity removal can be performed simultaneously.

  On the other hand, when it is desired to manufacture silicon on a large scale, it may be difficult to make the system completely in an inert gas atmosphere. From this point of view, if silicon can be manufactured in an air atmosphere, it is considered that silicon can be efficiently manufactured. Moreover, if it can manufacture in an air atmosphere, manufacturing cost can also be suppressed. However, as described above, in the air atmosphere, there is a problem that silica is generated by the reaction between oxygen and silicon, and the reaction interface decreases. This problem can be solved by, for example, the following silicon manufacturing method.

  That is, the process includes a step of bringing molten silicon containing impurities into contact with a treatment agent in a system containing oxygen, causing the impurities in the molten silicon to react with the treatment agent, and removing the impurities out of the system. An agent is supplied to the liquid surface portion and / or the inside of the molten silicon where the oxide generated by reacting with oxygen does not exist, and the processing agent is pushed below the liquid surface of the molten silicon. By using the silicon manufacturing method, it is possible to appropriately bring the molten silicon into contact with the treatment agent.

  In this case, for example, a portion where no oxide is present may be created in the liquid surface portion and / or inside of the molten silicon by moving the generated oxide to the liquid surface of the molten silicon.

  As for the movement of oxide, in addition to the form of moving using machines and tools, the form of moving the oxide in a certain direction by inducing and stirring the molten silicon by induction heating and inducing flow, or plasma It may be a form in which the oxide is moved or removed by treatment or the like.

  Alternatively, even if a treatment agent is added to the location where the oxide of the molten silicon exists, the treatment agent is pushed into a portion below the liquid level of the molten silicon to treat the portion of the molten silicon where no oxide exists. An agent can be supplied.

1.7. Step S7
Step S7 is a step of solidifying molten silicon in the system. The solidification of the molten silicon may be performed by cooling the molten silicon, such as casting the molten silicon into a mold. By solidifying the molten silicon, a high-purity silicon ingot from which impurities are removed can be obtained. Further, when the molten silicon is solidified, so-called unidirectional solidification is performed, and remaining impurities are removed by segregation, whereby higher purity silicon can be obtained.

  After removing the impurities by the above method, the alkali metal can be further removed to obtain higher-purity silicon. The alkali metal can be removed by a commonly used method known per se. For example, it is easily removed by processes such as vacuum processing and unidirectional solidification.

  Thus, in the manufacturing method S100, impurities in the molten silicon are removed by the steps S1 to S7. Then, after the removal of impurities is completed, the treatment agent may be removed by evaporation. Further, when it is desired to increase the purity, after removing the treatment agent by evaporation, a treatment agent is newly added, and the steps S3 to S6 are repeated again.

  Moreover, in manufacturing method S100, you may use a high purity processing agent and a low purity processing agent properly. For example, when the impurity concentration in the molten silicon is high, the impurities are removed to some extent using a low-purity treatment agent, and then the impurity concentration in the molten silicon is lowered (for example, 80% or more of the entire purification time has elapsed). Or when the boron concentration in the molten silicon becomes 1 ppm or less on the basis of mass), once the processing agent in the system is removed, a new processing agent (unused processing agent or recovered from outside the system) is removed. Then, the regenerated high-purity processing agent) is charged and pushed below the liquid level of the molten silicon, and then steps S4 to S6 may be performed.

  In the manufacturing method S100, the evaporated processing agent can be recovered and used again as the processing agent in the next and subsequent silicon purification. At this time, it is preferable to regenerate the treatment agent by removing impurities contained in the treatment agent by purification. With reference to FIG. 2, the process of recovering the processing agent (process S8) and the process of regenerating the processing agent (process S9) will be described.

1.8. Step S8
Step S8 is a step of recovering the processing agent from the system. For example, in the above step S5 or step S6, the treatment agent can be recovered.

  A processing agent containing concentrated impurities adheres and condenses on the closing means that has undergone step S5, and the processing agent can be recovered by scraping the condensate.

In addition, at the time of step S6, the processing agent (gaseous, liquid, or powder) can be recovered outside the system. For example, the processing agent can be collected by sucking and collecting the fumes containing the processing agent from the inside of the system to the outside of the system. At this time, the suction port and the distribution path are at a temperature higher than the melting point of the treatment agent from the viewpoint of being able to suck the treatment agent without unnecessary solidification at the suction port and preventing clogging of the treatment agent in the distribution path. It is preferable to set so that. Further, when the fumes are sucked together with the carrier gas, it is preferable that the wind speed (m · s ⁻¹ ) in the distribution channel is 5 or more and 30 or less. Also by this, adhesion of the processing agent in the distribution channel can be suppressed, and clogging of the distribution channel can be prevented. In suctioning, a suction port may be installed in the vicinity of the liquid surface of the processing agent or molten silicon. Accordingly, the temperature at the suction port can be easily set to a temperature equal to or higher than the melting point of the processing agent, and the evaporated processing agent can be efficiently sucked.

  For example, the fumes can be condensed by a cyclone or bag filter and recovered as a condensate. Alternatively, the fumes can be collected in a solvent by wet collection to form a slurry, and the slurry can be recovered as a massive condensate by drying. In this case, water is preferably used as the solvent. In addition, the following effects are also show | played by collect | recovering as a blocky aggregate through wet collection. That is, the massive aggregate can be melted and purified more easily than the powder in step S9 described later. This is considered to be because the voids are reduced and the density is increased by becoming a lump, resulting in an increase in thermal conductivity, and heat can be easily conducted to the inside. Thereby, the aggregate can be easily melted, and impurities existing inside can be efficiently removed and purified.

1.9. Step S9
Step S9 is a step of regenerating the treatment agent collected in step S8. In step S9, it can be regenerated by purifying the treatment agent. For example, by heating the treatment agent, impurities contained in the treatment agent can be removed, and the treatment agent can be regenerated. The heating temperature at the time of regenerating the treatment agent is, for example, about 400 to 1700 ° C., preferably 600 to 1600 ° C.

  In addition, the above-described massive treatment agent can be obtained by heating and sintering the treatment agent, or by cooling and solidifying the treatment agent after heating and melting. That is, by heating the treatment agent, impurities contained therein can be removed, and a massive treatment agent that can be suitably used for silicon production can be easily obtained.

  The regenerated treatment agent can be used as the treatment agent in step S3 or as a treatment agent arbitrarily supplied in step S6.

  As described above, the manufacturing method S100 reacts the intrusion step (steps S1 to S3) in which the processing agent is pressed below the liquid level of the molten silicon in the system, the impurities in the molten silicon and the processing agent, It is possible to reduce the processing agent that evaporates without contacting the molten silicon, and to react the processing agent without waste. Can contribute.

  In the silicon production method S100, after the treatment agent is added (step S3), the reaction is first performed in a closed system (step S4), and then the reaction is performed in an open system (step S5). However, the present invention is not limited to the embodiment. You may react by an open system immediately after adding a processing agent. Or it is also possible to react by an open system, adding a processing agent. In the present invention, since the processing agent is pushed below the liquid level of the molten silicon, the processing agent that evaporates without contacting the molten silicon can be reduced, and the reaction is not performed in a closed system. In both cases, impurities can be efficiently removed from the molten silicon. However, the treatment agent can be contributed to the reaction without waste by circulating the treatment agent in the reaction system or condensing the treatment agent, or the treatment agent can be recovered appropriately, and the treatment agent can be recovered. From the viewpoint of further reducing the loss, it is preferable to carry out the reaction in a closed system and then evaporate and remove the processing agent and impurities in an open system.

  Further, in the above description, in step S4, the reaction system is a closed system, the impurities in the molten silicon react with the treatment agent, the evaporated substance is condensed in the closing means, and in step S5, the closing means is renewed. Although it replaced with the closure means and demonstrated as what repeats process S3-process S5, this invention is not limited to the said form. In step S5, the closing means may be replaced with a new closing means, and steps S4 to S5 may be repeated without adding a new processing agent, or the closing means may be removed without performing step S5. Thus, the step S6 can be performed as it is from the step S4. Moreover, when performing process S6 as it is from process S4, you may perform process S3 simultaneously. That is, the reaction in the closed system (step S4) and the reaction in the open system (step S6) may be performed while continuously introducing the treatment agent from below the liquid level of the molten silicon (step S3).

2. Silicon Manufacturing Apparatus A manufacturing apparatus capable of performing the silicon manufacturing method according to the present invention will be described. An apparatus for producing silicon according to the present invention is a method of bringing molten silicon containing impurities into contact with a processing agent in the system, reacting the impurities in the molten silicon with the processing agent, and removing the impurities out of the system. This manufacturing apparatus is characterized in that the following (1) to (5) are provided in the system.
(1) A container having a bottom, a side, and an upper opening and filled with molten silicon containing impurities (2) Pushing means for pushing the treatment agent below the liquid level of molten silicon (3) Contains impurities Heating means for heating the molten silicon and the processing agent (4) Closing means for closing the container in order to make the reaction system a closed system (5) Evaporation from the molten silicon and the processing agent used when making the reaction system an open system Removal means to remove objects out of the system

  For example, by installing the container, the heating means, and the cooling means in a housing such as a chamber, the inside of the housing can be made “inside the system” and the outside of the housing can be made “outside the system”. By providing a discharge port as a removing means in a part of the casing, impurities can be evaporated and removed from the system to the outside through the discharge port during the purification of the molten silicon.

2.1. Container The container is filled with molten silicon and a processing agent, and the interface between the molten silicon and the processing agent is formed in the container to react the impurities in the molten silicon with the processing agent. Can do. The impurities are removed from the molten silicon out of the system through the upper opening and the discharging means by evaporating into the gas phase or dissolving in the processing agent. The material of the container is not particularly limited as long as the method for producing silicon according to the present invention can be performed, but it is preferable to use a container made of graphite or silicon carbide. The shape and size of the container may be appropriately determined according to the scale of the purification process (scale of the heating means).

2.2. Pushing means The pushing means is means for pushing the treatment agent below the liquid level of the molten silicon. For example, the pushing means 15 as shown in FIG. 3A and the pushing means 16 as shown in FIG.

  FIG. 3 (A) schematically shows a pushing means 15 capable of pushing the treatment agent on the liquid level of the molten silicon downward from the liquid level. As shown in FIG. 3 (A), the pushing means 15 has a container part 15a capable of capturing the processing agent on the liquid surface and a rod-like part 15b having the container part 15a fixed to the tip. The part 15a is provided with a hole 15c. A plurality of the holes 15c may be provided. According to such pushing means 15, the treatment agent is pushed downward from the molten silicon liquid level by pushing the rod-like portion 15b while capturing the treatment agent at the molten silicon liquid level by the vessel 15a. be able to. At this time, gas and molten silicon are trapped in the vessel part 15a together with the treatment agent, but the gas and liquid molten silicon escape upward from the holes 15c provided in the vessel part 15a. Further, it is possible to elute or eject the treatment agent from the hole 15c. In the pushing means 15, the inner diameter of the vessel portion 15a may be designed according to the inner diameter of the container. For example, the inner diameter of the vessel portion 15a can be about 1000 mm. The diameter of the hole 15c is preferably 2 mm or more from the viewpoint of preventing clogging, for example.

  In the form shown in FIG. 3 (B), the massive treatment agent 2 is fixed to the tip of the pushing means 16 that is a rod-like body. Even if it is such a form, the rod-shaped body 16 can be inserted in the system, and the block-shaped processing agent 2 can be pushed down below the liquid level of molten silicon.

  In this way, the pushing means is configured to push the treatment agent on the liquid level downwardly after adding the treatment agent to the molten silicon (FIG. 3A), bringing the treatment agent into contact with the molten silicon and lowering the liquid surface. Any of the forms to be pushed into (FIG. 3B) may be used. In addition to these, for example, the treatment agent can be pushed downward from the liquid surface of the molten silicon by pushing the treatment agent from the side surface of the container filled with molten silicon. In addition, although the material of the pushing means is not specifically limited, For example, it can be set as the material similar to said container. The size of the pushing means can be appropriately determined according to the scale of the silicon manufacturing apparatus.

2.3. Heating means The heating means is not particularly limited as long as it can heat the molten silicon filled in the container and the treatment agent. In particular, it is preferable to use an induction heating furnace because the molten silicon and the processing agent in the container are induction-stirred to promote the reaction.

2.4. Closing means The closing means is not particularly limited as long as it is provided above the upper opening of the container, and the reaction system is a closed system and condenses the volatiles from the molten silicon and the processing agent. What can drop an object from the upper opening part of a container to molten silicon is used suitably. For example, a lid member having a side wall extending in the vertical direction in the system and having an opening at the lower part and a closing part at the upper part can be provided. In the inside (hollow part) of such a lid member, a temperature distribution exists, and the temperature decreases as the distance from the container side increases. That is, the evaporated processing agent is cooled as it rises inside the lid member, and eventually condenses. The condensed treatment agent increases in density and spontaneously falls from the inside of the lid member to the upper opening of the container. The evaporated treatment agent may be cooled and condensed in the hollow space of the lid member, or may be condensed by adhering to the inner wall of the lid member. Even condensate adhering to the inner wall can be naturally dropped into the upper opening of the container by peeling off from the wall surface or flowing down from the wall surface. In this case, it is preferable to provide a means for applying vibration to the lid member because the treatment agent can be dropped. Or you may collect | recover, without dropping the adhering condensate, as demonstrated in said process S5.

  The shape and size of the lid member are not particularly limited. For example, a lid member having an opening of the same size as the upper opening of the container and having a side wall extending upward from the container can be used. The material of the lid member is not particularly limited as long as it can withstand the temperature in the system and does not easily react with the evaporated treatment agent. For example, it can be made of the same material as the container. Moreover, you may attach heat insulating materials, such as a ceramic, for temperature control around a cylindrical body. Further, the upper closing portion of the lid member may have a structure that allows only gas to escape. For example, the closed portion may be formed by a filter such as carbon felt.

  A partition member may be provided inside the lid member. The surface area inside the lid member can be increased by the partition member. The shape and material of the partition member are not particularly limited.

  On the other hand, the closing means may be a plate-like body extending in a direction intersecting with the vertical direction in the system. Even if it is such a form, the processing agent which evaporated can be condensed in the container side surface vicinity of a plate-shaped object. In particular, a water-cooled surface plate is preferable. This is because the evaporated treatment agent can be more appropriately condensed. About the material of a plate-shaped body, what is necessary is just to make it the same as the said cover member. Further, the shape and size of the plate-like body may be appropriately determined in consideration of the size of the container. In the case of a plate-like body, a gap or a hole may be provided as a gas escape path between the plate-like body and the container or part of the plate-like body. The installation position of a plate-shaped body should just be above the upper opening part of a container. In particular, it is preferable to provide at a position filled with the vapor of the processing agent in the system.

  In the closing means, if the evaporated processing agent is condensed below the melting point, the effect of dropping the processing agent can be expected. In particular, the closing means is preferably a means for cooling the evaporated treatment agent to below the freezing point. Therefore, it is preferable that the closing means is provided outside (above) the heating means in order to avoid an unnecessary temperature rise. For example, when the heating furnace is an induction furnace, it is preferable to use a lid member having a side wall extending upward from the coil, or a plate-like body provided above the coil.

  The surface on the molten silicon side of the closing means is preferably coated with an oxide or nitride, for example silica or silicon nitride. High purity silica or silicon nitride particles may be coated. By coating in this manner, the treatment agent can be easily prevented from sticking, and the treatment agent can be spontaneously dropped, and the treatment agent can be easily recovered.

2.5. Removal means The removal means is means for discharging / removing the evaporated substance from the molten silicon out of the system when the reaction system is an open system. An example of the removing means is a discharge port provided so as to communicate the inside and outside of the system. As described above, the discharge port can be provided in a part of a housing such as a chamber. In particular, it is preferably provided on the top of the housing.

  In the silicon manufacturing apparatus according to the present invention, the removing means may further include a suction means for sucking volatile matter (evaporated material) from the molten silicon liquid surface. The suction means preferably has a suction port provided above the liquid level of the molten silicon and in the vicinity of the liquid level. Thereby, the evaporated substance from the molten silicon liquid surface can be efficiently removed. The wind speed and the like at the suction port are as described above.

  Moreover, the silicon manufacturing apparatus according to the present invention may further include a recovery means for recovering volatile matter (evaporated matter) from the molten silicon liquid surface. The recovery means is preferably provided outside the system of the manufacturing apparatus. For example, when the treatment agent is removed by evaporation after the purification of silicon is completed, if the treatment agent removed by evaporation is recovered outside the system by the recovery means, it is reused as the treatment agent again at the next silicon purification. be able to. As a specific example of the recovery means, either a cyclone, a bag filter or a wet collection means is preferable. In particular, wet collecting means is preferred.

  When the reaction system is an open system, do not allow the closing means to function (for example, open a gap between the lid member or plate-like body and the container, or remove the lid member or plate-like body from the system. Etc.) Thereby, the reaction system can be an open system, and the evaporated material from the molten silicon liquid surface can be smoothly removed by evaporation by the removing means.

  Specific examples of the silicon manufacturing apparatus according to the present invention will be described in more detail, including other configurations other than those described above.

2.6.1. Silicon manufacturing apparatus 100
FIG. 4 schematically shows a silicon manufacturing apparatus 100 according to an embodiment of the present invention. The apparatus 100 includes a sealable chamber or a casing 7 that can be sealed with an inert gas such as argon, a container (crucible) 3 of graphite or the like disposed therein, a coil 4 for induction heating, a heat insulating material 8, a crucible. 3, and a mold 9 for casting silicon, and the raw metal silicon 1 is filled in the crucible 3. Further, the treatment agent 2 is pushed below the liquid level of the molten silicon 1 by the pushing means 15 provided in the system. Further, when the reaction system is a closed system, a lid member 13 as a closing means is installed above the crucible 3.

A gas introduction port 11, an exhaust port 12, a raw material input port 6, and the like are attached to the housing 7. The processing agent 2 is introduced into the system from the raw material inlet 6. When a vacuum vessel is used as the casing 7, the inside of the chamber can be controlled to a pressure range of about 0.01 to 2 × 10 ⁵ Pa (vacuum to 2 atm), but it is usually inert such as Ar. It is more economical to use a gas seal housing.

  In addition, the heating induction coil 4, the heat insulating material 8, and the crucible 3 can be tilted together, and the processed raw metal silicon 1 is poured into the mold 9.

  In the production of silicon, first, the gap between the lid member 13 and the crucible 3 above the crucible 3 is opened, and the raw material metal silicon 1 is filled in the crucible 3 and heated to obtain molten silicon. A predetermined amount of the processing agent 2 is introduced from the raw material inlet 6 into the liquid surface of the molten silicon. After the charging, the processing agent 2 is pushed downward from the liquid surface of the molten silicon 1 using the pushing means 15. Thereafter, the lid member 13 is installed again above the crucible 3 and the reaction system is closed. The charged processing agent 2 evaporates after being heated and melted, but when the vapor rises in the lid member 13, it cools and condenses, becomes liquid or solid, and drops naturally into the crucible 3 again because of its high density. Cycle by doing. As a result, it is possible to reduce the treatment agent that is not involved in the reaction and evaporates wastefully. Thus, after reacting in a closed system, a reaction system is made into an open system. In this case, for example, a gap may be provided between the lid member 13 and the crucible 3 or the lid member 13 may be removed from the system. Impurities in the silicon 1 react with the treating agent 2 to form a gaseous reaction product, so that the impurities are removed from the upper opening of the crucible 3 through the outlet and the molten silicon is purified. At this time, the treatment agent remaining in the molten silicon is also removed by evaporation. However, since the impurities are also dissolved in a small amount in the treatment agent, the molten silicon is also purified by this process. If necessary, the molten silicon 1 is highly purified by repeating these processes.

2.6.2. Silicon manufacturing apparatus 200
FIG. 5 schematically shows a silicon manufacturing apparatus 200 according to an embodiment of the present invention. The manufacturing apparatus 200 is not provided with the raw material charging port 6, and the manufacturing apparatus is configured to push the processing agent 2 below the liquid level of the molten silicon 1 using the pushing means 16 instead of the pushing means 15. The configuration is the same as 100. Even if it is such a structure, the processing agent 2 can be pushed down rather than the liquid level of the molten silicon 1, and a processing agent can be contributed to reaction without waste.

2.6.3. Silicon manufacturing apparatus 300
FIG. 6 schematically shows a silicon manufacturing apparatus 300 according to an embodiment of the present invention. In the apparatus 300 of FIG. 6, considering that it is advantageous for impurity treatment to move the interface between both liquid phases of the molten silicon 1 and the treatment agent 2, argon or the like which is an inert gas is gasified in the liquid phase. The liquid phase is agitated by blowing through the blowing tube 25, and the contact state at the interface between the two liquid phases can be improved. By doing so, the reaction product of impurities can be efficiently driven out together with the inert gas. In this case, a gap may be provided between the lid member 13 and the crucible 3 as a gas escape path.

  Regarding the stirring of the molten silicon 1, instead of the gas blowing as described above, the silicon liquid phase is induced and stirred using a high frequency induction furnace, or the stirring plate is rotated in the molten silicon 1 to stir the liquid phase. This method is also effective. In the case of induction heating, it is desirable to use a power source having a relatively low frequency, for example, about 0.5 to 5 KHz, because an induced current is generated in the silicon melt and a specific stirring phenomenon occurs. In particular, in this case, the melt can be stirred without mechanical stirring by inserting a stirring plate or the like into the silicon melt, which is preferable from the viewpoint of contamination.

2.6.4. Silicon manufacturing apparatus 400
In the above description, it has been described that the closing means is provided. However, the silicon manufacturing apparatus capable of performing the silicon manufacturing method according to the present invention may have a form without the closing means. FIG. 7 schematically shows a silicon manufacturing apparatus 400 according to an embodiment. In the apparatus 400 of FIG. 7, the suction means 30 is provided instead of the closing means. The suction means 30 is provided at a position where the suction port faces the liquid surface of the molten silicon 1. Moreover, since the suction port is provided inside the crucible 3 (below the upper opening), it is possible to efficiently suck the evaporated processing agent. Thereby, it is possible to efficiently suck the treatment agent without condensing it at the suction port. Further, in the present invention, the pushing means 15 is used to push the charged processing agent 2 below the liquid surface of the molten silicon 1, so that the processing agent 2 is appropriately reacted in the liquid of the molten silicon 1. Even when the suction means 30 is present, it is possible to suppress the treatment agent 2 from being evaporated and sucked without contributing to the reaction.

Here, in order to efficiently suck the evaporated processing agent and impurities, the wind speed (m · s ⁻¹ ) at the uppermost end of the container side wall filled with molten silicon and the processing agent is set to 0.5 or more. It is preferable. It is preferable to reduce the diameter of the flow path in order to increase the wind speed and prevent the treatment agent from adhering to the wall of the path, but if it is too small, the pressure loss increases. Therefore, it is preferable to determine the diameter and the air volume of the flow path so that the wind speed (m · s ⁻¹ ) of the flow path is 5 or more and 30 or less.

  In such a form, in order to purify the collected processing agent, it is preferable to further include a heating means for melting the processing agent outside the system. Impurities dissolved and remaining in the treating agent can be removed by heating and melting the collected treating agent. The form of the recovery means is as described above.

  The silicon manufacturing apparatus 100 (or 200) and the manufacturing apparatuses 300 and 400 may be combined. That is, after the treating agent 2 is pushed below the liquid level of the molten silicon 1 using the pushing means 15 (or 16), the closing means 13 is blown into the molten silicon 1 via the gas blowing means 25. The reaction is carried out in a closed system, and then the closing means 13 is removed to make an open system, and the removing means including the suction means 30 is used to suck out volatiles (evaporates) from the molten silicon liquid surface. The agent and impurities may be removed from the system.

  According to the silicon manufacturing apparatus as described above, the silicon manufacturing method according to the present invention can be appropriately implemented. The impurity concentration of silicon obtained by the method for producing silicon according to the present invention is preferably 2.0 ppm or less, more preferably 1.5 ppm or less, further preferably 1.0 ppm or less, and 0.5 ppm or less for boron (B). Is particularly preferred. Moreover, about aluminum (Al), 20 ppm or less is preferable normally, 18 ppm or less is more preferable, 2 ppm or less is further more preferable, and 1 ppm or less is especially preferable. Furthermore, about calcium (Ca), 20 ppm or less is preferable normally, 5 ppm or less is more preferable, 2 ppm or less is further more preferable, and 1 ppm or less is especially preferable. In addition, in the manufacturing method which concerns on this invention, impurity concentration can also be made still smaller than the said value by repeating said process S4-6 many times.

  The impurity concentration in silicon can be analyzed by, for example, ICP-MS (Inductively Coupled Plasma Mass Spectrometer).

  Silicon obtained by the method for producing silicon according to the present invention may be further purified by combining other purification methods.

3. Use of silicon Silicon obtained by the method for producing silicon according to the present invention can be used as, for example, a silicon ingot for a solar cell or a silicon wafer by processing it by a known method. Alternatively, it can be used as high-purity silicon used as a material for producing a solar cell panel.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein. The silicon manufacturing method and manufacturing apparatus, silicon wafer, and solar cell panel can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification. Moreover, it should be understood as being included in the technical scope of the present invention.

  Silicon obtained by the method for producing silicon according to the present invention can be used as a material for a silicon wafer or a solar cell panel.

1 Molten silicon 2 Treatment agent 3 Crucible (container)
4 Coils (heating means)
6 Raw material input (input pipe)
7 Housing 8 Heat insulating material 9 Mold 10 Support base 11 Gas inlet 12 Exhaust outlet (removing means)
13 Lid member (closing means)
DESCRIPTION OF SYMBOLS 15 Pushing means 16 Pushing means 25 Gas blow-in pipe 30 Suction means 100, 200, 300, 400 Silicon manufacturing apparatus

Claims (13)

An indentation step of pushing the treatment agent below the liquid level of the molten silicon in the system;
A reaction step of reacting the impurities in the molten silicon with the treatment agent and removing the impurities out of the system,
Silicon manufacturing method.   The treatment agent is in the form of a lump, and in the indentation step, the treatment agent and the molten silicon are brought into contact with each other by introducing the lump treatment agent into the liquid surface of the molten silicon, and the treatment agent is used by pushing means. The silicon manufacturing method according to claim 1, wherein the silicon is pushed below the liquid level of the molten silicon.   The treatment agent is in a lump shape, and the treatment agent is brought into contact with the molten silicon and fixed on the liquid surface of the molten silicon by fixing the lump treatment agent to the rod-like body and inserting the rod-like body into the system. The method for producing silicon according to claim 1, wherein the silicon is pushed downward.   The method for producing silicon according to claim 1, wherein the impurities include boron.   The manufacturing method of the silicon | silicone as described in any one of Claims 1-4 whose said processing agent is a salt.   The treatment agent is a group consisting of a salt of alkali metal and halogen, a salt of alkaline earth metal and halogen, a composite salt containing alkali metal and halogen, and a composite salt containing alkaline earth metal and halogen. The manufacturing method of the silicon | silicone as described in any one of Claims 1-5 which contains the at least 1 sort (s) of compound chosen from these. The treatment agent is lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), rubidium fluoride (RbF), cesium fluoride (CsF), sodium silicofluoride (Na ₂ SiF ₆ ). At least selected from the group consisting of cryolite (Na ₃ AlF ₆ ), a mixture of sodium fluoride and barium fluoride, a mixture of sodium fluoride, barium fluoride and barium chloride, and a mixture thereof The manufacturing method of the silicon | silicone as described in any one of Claims 1-6 containing 1 type of compounds.   The manufacturing method of the silicon | silicone as described in any one of Claims 1-7 whose quantity of the said processing agent is 5 to 300 mass% with respect to the said molten silicon. An apparatus for producing silicon, which comprises bringing molten silicon containing impurities into contact with a treatment agent in the system, reacting the impurities in the molten silicon with the treatment agent, and removing the impurities out of the system,
In the system,
A container having a bottom, a side, and an upper opening, and filled with molten silicon containing the impurities,
A pushing means for pushing the treatment agent below the liquid level of the molten silicon;
A heating means for heating the molten silicon containing the impurities and the treatment agent; and
Removing means for removing the evaporated material from the molten silicon and the treatment agent out of the system;
A silicon manufacturing apparatus.   The silicon manufacturing apparatus according to claim 9, wherein the pushing means pushes a massive treatment agent present on the liquid surface of the molten silicon downwardly of the liquid surface.   The silicon manufacturing apparatus according to claim 9, wherein the pushing means is a rod-like body capable of fixing a massive treatment agent at a tip.   The silicon wafer using the silicon obtained by the manufacturing method of the silicon | silicone as described in any one of Claims 1-8.   The panel for solar cells using the silicon obtained by the manufacturing method of the silicon | silicone as described in any one of Claims 1-8.

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