JP2013086994A - Method 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 step of adding the treating agent to molten silicon in a system, and a step of reacting the treating agent with the impurities in the molten silicon and removing the impurities from the system, wherein the treating agent has a median diameter of ≥70 μm.

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 investigations to solve the above problems, the present invention can appropriately prevent the treatment agent from being scattered in the system by using a treatment agent having a median diameter of a predetermined value or more. The present inventors have found that the treatment agent can be surely reached molten silicon and added without waste. As a result, the treatment agent could be reliably brought into contact with the molten silicon and efficiently contributed to the reaction with the impurities. The present invention has been accomplished based on the findings.

That is, the gist of the present invention resides in the following (1) to (10).
(1) a step of adding a treatment agent to molten silicon in the system, and a step of reacting impurities in the molten silicon with the treatment agent to remove the impurities out of the system. The method for producing silicon, wherein the median diameter is 70 μm or more.
(2) The method for producing silicon according to (1), wherein the impurities include boron.
(3) The method for producing silicon according to (1) or (2), wherein the treating agent is a salt.
(4) 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 (3), comprising at least one compound selected from the group consisting of:
(5) 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 (4), comprising at least one selected compound.
(6) The manufacturing method of the silicon | silicone as described in any one of (1)-(5) whose quantity of the said processing agent is 5 mass% or more and 300 mass% or less with respect to the said molten silicon.
(7) The method for producing silicon according to any one of (1) to (6), further including a step of obtaining the treatment agent having a median diameter of 70 μm or more by heating the treatment agent.
(8) After recovering the used treatment agent, it is heated to remove the impurities contained in the treatment agent and further to obtain the treatment agent having a median diameter of 70 μm or more. (7) The method for producing silicon according to any one of (7).
(9) A silicon wafer using silicon obtained by the method for producing silicon according to any one of (1) to (8).
(10) 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 “median diameter” means the 50% diameter (d50) of the cumulative distribution based on the volume, ie, the median diameter, of the particle diameter measured using a laser diffraction particle size distribution analyzer. .
In the case of a processing agent with a large particle size that cannot be measured by a laser diffraction particle size distribution analyzer (for example, a processing agent in which particles or lumps of 3.5 mm or more are present in a weight fraction of 51% or more), chemical products of JIS K 0069 Means the median diameter determined by the screening test method.

  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 phase The interface can be configured, 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, a treatment agent having a particle diameter of a predetermined size or more is introduced into the system, and scattering of the treatment agent in the system can be suppressed. 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 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 includes a step of adding a treatment agent to molten silicon in the system, and reacting impurities in the molten silicon with the treatment agent to remove the impurities out of the system. And the median diameter of the treatment agent is 70 μm or more. The “median diameter” means the 50% diameter (d50) of the cumulative distribution on the basis of the volume of particles measured using a laser diffraction particle size distribution analyzer, that is, the median diameter. A processing agent having a large particle size that cannot be measured with a laser diffraction particle size distribution analyzer (for example, when particles or lumps of 3.5 mm or more have a weight fraction of 51% or more) is a JIS K 0069 chemical product screening test method. Means the median diameter determined by

  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 heating and melting the injected silicon (step S2), and a treatment agent having a predetermined particle diameter in the molten silicon. Adding step (step S3), reacting molten silicon with the processing agent in a closed system (step S4), replacing the closing means (step S5), with the closing means removed, 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 a step of solidifying 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 a treatment agent having a predetermined particle diameter to 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.

  The treatment agent to be added has a median diameter of 70 μm or more, preferably 80 μm or more, more preferably 100 μm or more, and particularly preferably 200 μm or more. If it is such a magnitude | size, when adding a processing agent in molten silicon, it can prevent that a processing agent scatters etc., and it becomes possible to make a processing agent and an impurity react efficiently. The upper limit of the median diameter of the treatment agent may be any size that can be charged into the system, but is, for example, 100 cm or less, preferably 50 cm or less, more preferably 20 cm or less, and particularly preferably 10 cm or less. If it is such a magnitude | size, when adding a processing agent to molten silicon, it can prevent that molten silicon scatters, and it becomes possible to make it react safely and efficiently.

  The form of the treatment agent in the present invention may be, for example, a form composed of primary particles having a median diameter of 70 μm or more, or primary particles having a median diameter of less than 70 μm are sintered, or after heating and melting. The form which consists of a secondary particle and a lump with a median diameter of 70 micrometers or more obtained by making it cool and solidify may be sufficient. As a method for producing a treatment agent having such a median diameter, for example, by arbitrarily crushing the powder treatment agent after sintering, or by once heating and dissolving the powder treatment agent, A treatment agent having a median diameter of 70 μm or more can be obtained by arbitrarily crushing after cooling and solidification. In addition, the impurity contained in a processing agent can also be removed by heating a processing agent.

  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 the impurities are evaporated at the treatment temperature. So there is no problem. Therefore, it is possible to use a normal industrial chemical as the treating agent. However, in the present invention, the impurities in the treatment agent can be removed by heating, and the treatment having a predetermined median diameter can be performed by sintering as it is, or by cooling and solidifying after melting. An agent can be obtained.

  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.

  In the above description, only the raw material metal silicon is heated and melted to obtain molten silicon, and then the treatment agent is added thereto. However, as a mode of forming a liquid phase interface between the molten silicon and the treatment agent, For example, the raw metal silicon and the treatment agent may be mixed and then heated and dissolved at the same time. When the raw material metal silicon and the processing agent are mixed and heated and melted, the processing agent evaporates until the silicon melts. In the present invention, the molten silicon and the processing agent are reacted in a closed system by the step S4 described later. The loss of the processing agent can be suppressed. 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.

  However, from the viewpoint of suppressing the evaporation of the treatment agent and using it efficiently, preferably, only the raw metal silicon is heated and melted to form molten silicon, and then the treatment agent is added thereto.

  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, a treatment agent having a predetermined median diameter is added, so that the treatment agent can be prevented from scattering and the treatment agent can reliably reach the molten silicon liquid surface. 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. It can be transferred into 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, most of the treatment agent evaporates without reacting with impurities in the molten silicon. 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 upper treatment agent into the lower silicon layer. Alternatively, a method of mechanically pushing up the lower processing agent 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 a processing agent having a predetermined particle diameter to the molten silicon again, This is a step of removing the processing agent and impurities out 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. By supplying the agent to the liquid surface portion and / or the inside of the molten silicon, and to the portion where the oxide generated by reacting with oxygen is not present, the molten silicon and the treatment agent Can be properly brought into contact with each other.

  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.

  Furthermore, the form which supplies a processing agent to the part in which the oxide does not exist in the inside of molten silicon by pushing a processing agent in the inside of molten silicon may be sufficient.

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 treatment agent) may be added, 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, the processing agent can be recovered from the above step S5 or step S6.

  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.

  It is also possible to obtain a treatment agent having a median diameter of 70 μm or more 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 treatment agent having a predetermined median diameter that can be suitably used for silicon production can be easily obtained.

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

  As described above, in the manufacturing method S100, the step of adding the treatment agent to the molten silicon in the system (steps S1 to S3), the impurities in the molten silicon and the treatment agent are reacted, and the impurities are removed from the system. And the processing agent (steps S4 to S6) has a median diameter of 70 μm or more, the scattering of the processing agent in the system can be prevented and the processing agent can be used effectively.

  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 S6). 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 a processing agent having a median diameter of 70 μm or more is used, it is possible to prevent scattering of the processing agent in the system, and to ensure that the processing agent reaches the liquid level of the molten silicon. Impurities can be efficiently removed from the molten silicon without performing a reaction. 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 (4) are provided in the system.
(1) A container having a bottom, a side, and an upper opening and filled with molten silicon containing impurities and a processing agent. (2) Heating means for heating the molten silicon containing impurities and the processing agent. Closing means for closing the container to make the reaction system closed (4) Removal means for removing the evaporated silicon and molten material from the processing agent used when the reaction system is made open

  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. 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.

2.3. 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.

2.4. 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 at the suction port is 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.

2.5.1. Silicon manufacturing apparatus 100
FIG. 3 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, a casting mold 9 for casting silicon, and the like. The raw metal silicon 1 and the treatment agent 2 are filled in the crucible 3 in the form of liquid phase separation. Moreover, when making a reaction system into a closed system, the cover member 13 as a closing means is installed above the crucible b3.

A gas introduction port 11, an exhaust port 12, a raw material input port 6, and the like are attached to the housing 7. 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 treatment agent having a predetermined particle diameter is introduced into the molten silicon liquid surface from the raw material inlet 6 and then the lid member 13 is placed again above the crucible 3 to close the reaction system. System (state shown in FIG. 3). The charged treatment agent 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 naturally drops again into the crucible 3 because of its high density. Cycle through things. 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 dissolved in a trace amount in the remaining treatment agent, the molten silicon is also purified by this process. If necessary, the molten silicon 1 is highly purified by repeating these processes.

2.5.2. Silicon manufacturing apparatus 200
FIG. 4 schematically shows a silicon manufacturing apparatus 200 according to an embodiment of the present invention. In the apparatus 200 of FIG. 2, in view of the fact that it is advantageous for impurity treatment to move the interface between both liquid phases at the time of the reaction between the molten silicon 1 and the treatment agent 2, argon, which is an inert gas in the liquid phase. Etc. are blown through the gas blowing tube 25 to stir the liquid phase, thereby making it possible to improve the contact state at the interface between the two liquid phases. By doing so, the reaction product of impurities at the interface 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.

2.5.3. Silicon manufacturing apparatus 300
In the above description, it has been described that the closing means is essential, but the silicon manufacturing apparatus capable of performing the silicon manufacturing method according to the present invention is not limited to this mode. FIG. 5 schematically shows a silicon manufacturing apparatus 300 according to an embodiment. In the apparatus 300 of FIG. 5, 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 surfaces of the molten silicon 1 and the processing agent 2. 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. In the present invention, since the treatment agent having a predetermined particle diameter is used, the introduced treatment agent can reach the liquid level of the molten silicon without being sucked by the suction means 30.

Here, in order to efficiently suck the processing agent and impurities evaporated from the liquid surface of the molten silicon, the wind speed (m · s ⁻¹ ) at the uppermost end of the container side wall filled with the molten silicon and the processing agent is It is preferable to set it to 0.5 or more. 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 heating the processing agent outside the system. By heating the collected treatment agent, impurities dissolved and remaining in the treatment agent can be removed. The form of the recovery means is as described above.

  A combination of the silicon manufacturing apparatuses 100, 200, and 300 is also possible. That is, after reacting in the closed system using the closing means while blowing gas into the molten silicon, the closing means is removed to make the open system, and the removal means having the suction means removes the volatilization from the molten silicon liquid surface. It is good also as what removes a processing agent and impurities out of a system, sucking a thing (evaporated material).

  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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not restrict | limited by a following example, unless the summary is exceeded.

  In the following examples and comparative examples, raw metal silicon having impurity concentrations shown in Table 1 was used. The impurity concentration (ppm) in silicon is a value (mass standard) analyzed by ICP-MS (Inductively Coupled Plasma Mass Spectrometer).

  In Examples 1 to 3, NaF having a median diameter of 280.8 μm was used as the treating agent, and in Comparative Examples 1 and 2, NaF having a median diameter of 54.5 μm was used as the treating agent. The particle size of the treatment agent was measured by laser diffraction measurement (JIS Z8825-1). The “median diameter” means the 50% diameter (d50) of the cumulative distribution on the basis of the volume of particles measured using a laser diffraction particle size distribution analyzer, that is, the median diameter.

Example 1
Silicon was purified using an apparatus as shown in FIG. Specifically, after sealing with argon, the inside of the housing 7 was set to atmospheric pressure, 3.0 kg of raw material metal silicon for purification was placed in the graphite crucible 3, and heated and dissolved at about 1480 ° C. Then, after charging 3.0 kg of NaF from above the liquid level of the molten silicon through the charging tube 6, the lid member 13 having the same shape as that obtained by inverting the crucible 3 is put on the upper part of the crucible 3 and closed. The system was reacted for 6 hours. Thereafter, the lid member 13 was removed from the upper part of the crucible 3, and all NaF was removed by evaporation. Finally, the crucible 3 was tilted, and silicon was tilted into the mold 9 to be solidified.

Example 2
Silicon was purified using an apparatus as shown in FIG. Specifically, after sealing with argon, the inside of the housing 7 was brought to atmospheric pressure, 3.0 kg of raw material silicon metal for purification was put into a graphite crucible 3, and heated and dissolved at about 1490 ° C. Then, after charging 3.0 kg of NaF from above the liquid level of the molten silicon through the charging tube 6, the lid member 13 having the same shape as that obtained by inverting the crucible 3 is put on the upper part of the crucible 3 and closed. The system was reacted for 6 hours. Thereafter, the lid member 13 was removed from the upper part of the crucible 3, and all NaF was removed by evaporation. Finally, the crucible 3 was tilted, and silicon was tilted into the mold 9 to be solidified.

Example 3
Silicon was purified using an apparatus as shown in FIG. Specifically, after sealing with argon, the inside of the housing 7 was set to atmospheric pressure, 3.0 kg of raw material metal silicon for purification was placed in the graphite crucible 3, and heated and dissolved at about 1480 ° C. Then, after 1.5 kg of NaF was introduced from above the liquid level of the molten silicon through the introduction pipe 6, the lid member 13 having the same form as that obtained by inverting the crucible 3 was put on the upper part of the crucible 3 and closed. The system was reacted for 6 hours. Thereafter, the lid member 13 was removed from the upper part of the crucible 3, and all NaF was removed by evaporation. Finally, the crucible 3 was tilted, and silicon was tilted into the mold 9 to be solidified.

Comparative Example 1
Silicon was purified using an apparatus as shown in FIG. Specifically, after sealing with argon, the inside of the housing 7 was set to atmospheric pressure, and 3.0 kg of raw material silicon metal for purification was placed in the graphite crucible 3 and heated and dissolved at about 1485 ° C. After that, 1.2 kg of NaF was introduced from above the liquid level of the molten silicon through the introducing pipe 6, and then the lid member 13 having the same form as that obtained by inverting the crucible 3 was put on the crucible 3 and closed. The system was reacted for 4.5 hours. Thereafter, the lid member 13 was removed from the upper part of the crucible 3, and all NaF was removed by evaporation. Finally, the crucible 3 was tilted, and silicon was tilted into the mold 9 to be solidified.

Comparative Example 2
Silicon was purified using an apparatus as shown in FIG. Specifically, after sealing with argon, the inside of the housing 7 was set to atmospheric pressure, 3.0 kg of raw material metal silicon for purification was placed in the graphite crucible 3, and heated and dissolved at about 1480 ° C. Then, after charging 3.0 kg of NaF from above the liquid level of the molten silicon through the charging tube 6, the lid member 13 having the same shape as that obtained by inverting the crucible 3 is put on the upper part of the crucible 3 and closed. The system was reacted for 7.5 hours. Thereafter, the lid member 13 was removed from the upper part of the crucible 3, and all NaF was removed by evaporation. Finally, the crucible 3 was tilted, and silicon was tilted into the mold 9 to be solidified.

  In Table 1 below, for Examples 1 to 3 and Comparative Examples 1 and 2, the boron concentration, aluminum concentration and calcium concentration contained in silicon before purification (raw metal silicon), and the boron concentration contained in silicon after purification The aluminum concentration and calcium concentration are shown. In addition, the yield of purified silicon and the concentration of boron contained in NaF recovered after silicon purification are also shown.

  As is clear from the results in Table 1, Examples 1 to 3 using NaF having a median diameter of 280.8 μm as the treating agent are Comparative Examples 1 and 2 using NaF having a median diameter of 54.5 μm as the treating agent. As compared with, boron, aluminum and calcium (particularly boron and aluminum) contained in silicon could be removed, and high-purity silicon could be obtained. In addition, since Examples 1 to 3 have a higher boron concentration in the recovered NaF than Comparative Examples 1 and 2, NaF having a large median diameter is used particularly for efficiently removing boron. It can be said that it is preferable. That is, in Examples 1 to 3, by using a treatment agent having a particle diameter of a predetermined value or more, it is possible to appropriately prevent the treatment agent from being scattered in the system and to ensure that the treatment agent is molten silicon. As a result, it was considered that the treatment agent and the impurities could be reacted efficiently as a result of using the treatment agent without waste. On the other hand, in Comparative Examples 1 and 2, the processing agent scatters in the system when charged, or melts and evaporates due to heat in the system, and the processing agent is discharged out of the system without coming into contact with the molten silicon. It is thought that.

  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, silicon wafer, and solar cell panel with such changes can also be appropriately changed without departing from the spirit or concept of the invention that can be read from the claims and the entire specification. Should be understood as being included in the technical scope of

  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)
25 Gas blowing tube 30 Suction means 100, 200, 300 Silicon production apparatus

Claims (10)

Adding a processing agent to molten silicon in the system;
Reacting the impurities in the molten silicon with the treatment agent, and removing the impurities out of the system,
The median diameter of the treatment agent is 70 μm or more,
Silicon manufacturing method.   The method for producing silicon according to claim 1, wherein the impurities include boron.   The method for producing silicon according to claim 1, wherein the treatment 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 1-3 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 1-4 containing 1 type of compounds.   The manufacturing method of the silicon | silicone as described in any one of Claims 1-5 whose quantity of the said processing agent is 5 to 300 mass% with respect to the said molten silicon.   The manufacturing method of the silicon | silicone as described in any one of Claims 1-6 which further has the process of obtaining the said processing agent with a median diameter of 70 micrometers or more by heating a processing agent.   The process according to any one of claims 1 to 7, further comprising a step of recovering the treatment agent after use to remove the impurities contained in the treatment agent and obtaining the treatment agent having a median diameter of 70 µm or more. A method for producing silicon according to claim 1.   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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