JP2005220002A - APPARATUS FOR REFINING SiO, METHOD OF REFINING SiO USING THE SAME, AND METHOD OF MANUFACTURING HIGH PURITY SILICON USING THE OBTAINED SiO - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of refining SiO with a high content of P and a method of manufacturing high purity SiO using the SiO. <P>SOLUTION: The apparatus for refining SiO is equipped with an SiO gas reservoir which is installed between an SiO generator and an SiO condenser. The apparatus is used for the method of refining SiO and the obtained SiO is used as a raw material for the method of manufacturing high purity Si. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus for purifying SiO, a method for purifying SiO using such a purifier, and a method for producing high-purity silicon using the obtained SiO. More specifically, the present invention relates to a process for producing high-purity silicon usable for solar cells. .

  The Si used for the solar cell substrate is required to have an extremely high purity of 99.9999% or higher (hereinafter, Si having this level of purity is referred to as “high purity Si” and has a lower purity than this. This is referred to as “low purity Si”). In particular, impurity elements in Si, which adversely affect battery performance, are phosphorus, arsenic, antimony, boron, gallium, n-type impurity elements or p-type impurity elements that significantly reduce the electromotive force generated by sunlight. Indium and other metal elements that lower the electrical resistance to inhibit the insulation of the element and inhibit the movement of electric charges generated in the battery, such as iron, aluminum, nickel, and titanium. High-purity Si has heretofore been produced by the Siemens method (Patent Document 1, etc.). In this method, a metal silicon raw material having a purity of about 97% is once chlorinated, then purified and reduced to obtain high-purity silicon of 99.9999999% or more. In addition, the manufacturing cost is unavoidable.

  Therefore, a method for producing high-purity Si once from metal Si or the like via silicon monoxide (SiO) has been proposed. For example, Patent Document 2 discloses a method for obtaining high-purity Si from SiO by the following reaction at a high temperature.

SiO → Si + SiO ₂ (1)
In Patent Document 3,
SiO + H ₂ → Si + H ₂ O (2)
It is shown that Si can be obtained from SiO by the following reaction.
As a method for obtaining SiO, for example, as shown in Patent Document 4, a technique based on the following two reactions is known.

Si + SiO ₂ → 2SiO (3)
C + SiO ₂ → SiO + CO (4)
This is a large endothermic reaction that occurs under high temperature and low pressure. This method comprises a furnace for decompressing a mixture of SiO ₂ powder and metal silicon powder, a recovery device for recovering the SiO powder, and an airtight conveyance path connecting the furnace and the recovery device. Implemented by the device.

As another method for obtaining SiO, Patent Document 5 uses Si vaporized by a plasma jet,
2Si + O ₂ → 2SiO (5)
It is disclosed that SiO fine powder is obtained by the following reaction.

Furthermore, as another method for obtaining SiO, in Patent Document 6, for example, by burning silane (SiH ₄ ) gas in a hydrogen gas atmosphere,
_{SiH 4 + O → 2SiO + H} 2 (6)
It is disclosed that SiO fine powder is obtained by the following reaction.

  In these production methods for obtaining SiO in fine powder, compared to production methods for obtaining SiO in bulk in terms of handling fine powder and safety measures during production (SiO fine powder explodes when exposed to room temperature air). Manufacturing costs increase. Therefore, the method of obtaining SiO as fine powder as a high-purity Si production raw material is disadvantageous.

On the other hand, in the manufacture of SiO other than for solar cell substrates, for example, the manufacture of SiO deposited films, SiO may be the final product, and the optimum SiO component has been investigated and disclosed. For example, in Patent Document 7, as an SiO film for packaging foods and pharmaceuticals, impurity elements Fe, Al, Ca, Cu, Cr, Mn, Mg, Ti, Ni, P, As, Cd, Hg, Sb in SiO , Pb defines a range for the total amount. However, when this component system is directly used as the SiO for the Si raw material for the solar cell substrate, the battery performance is significantly varied. This is not specified in the art in terms of the component range of p-type impurities such as boron, which has a great influence on battery characteristics, and a specific element that has a particularly bad influence on battery performance, For example, even if P is contained in SiO at an unacceptable level for a solar cell substrate of the order of 10 ppm, if the total amount with other element component values is less than the reference value (50 ppm), Patent Document 7 This is because the standard is satisfied.
Japanese Patent Publication No. 35-2982 WO99 / 33749 US Patent No. 3010797 Japanese Patent Publication No. 4-81524 JP-A-60-215514 Japanese Patent Laid-Open No. 62-123209 JP 2002-194535 A

  In the conventional technique for producing Si from SiO, the final Si purity depends on the SiO purity as a raw material. However, in the prior art, although the impurities in the final Si product are well investigated for many elements, the interest in impurities in SiO is low, and a small number of components such as Fe, Al, P, etc. Only investigations and disclosures have been made. As a result, high-purity Si was produced using SiO having a large component variation as a raw material, so that the battery characteristics of the final Si product were not stable, the product yield was low, and inexpensive production was difficult. Here, there is a possibility that such a problem can be avoided if the reaction of the formula (3) is performed by using an extremely high purity raw material, for example, poly-Si for semiconductor, to generate SiO. No knowledge has yet been disclosed about the variation in the components of SiO obtained by various manufacturing methods. Also, using Si manufactured by using expensive poly Si for semiconductors for solar cell substrate Si, which is required to be produced in a low cost and in large quantities, is essentially unsatisfactory.

  On the other hand, conventionally, when Si is produced by the reaction of formula (1) using SiO containing a high concentration of P as a raw material, there is no particular P removal action, so P remains in Si at a high concentration. For this reason, there was a problem that the manufactured Si as it is cannot be applied as a material for a solar cell substrate.

  Among the impurity elements, P is a problem in the production of high purity Si. This is due to the following three reasons. First, even if P is a trace amount, it has a great adverse effect on battery characteristics. Secondly, a large amount of P is contained in raw materials that are inexpensive and available in large quantities, such as metal Si. Third, solidification purification, which is generally said to be effective for many impurity elements, has little effect on P and cannot be easily removed from Si.

  Therefore, when Si is produced by the reaction of the formula (1) using SiO containing a high concentration of P as a raw material, there is no particular P removal action, so P remains in Si at a high concentration. For this reason, there was a problem that the manufactured Si as it is cannot be applied as a material for a solar cell substrate.

  Accordingly, an object of the present invention is to provide an apparatus for purifying SiO having a low P concentration from an SiO raw material having a high P concentration.

  Another object of the present invention is to provide a method for purifying SiO having a low P concentration from a SiO material having a high P concentration.

  A further object of the present invention is to provide a method for producing high purity Si using such purified SiO.

  The present invention relates to a SiO purification apparatus comprising a SiO gas retention device between a SiO generator and a SiO condenser.

  The present invention also relates to a method for purifying SiO, characterized in that the apparatus is used.

A method of reducing the P concentration in the condensed SiO by setting P vapor in SiO to P ₂ or P _{4 in the} SiO gas retaining device is preferable.

  A method of introducing hydrogen gas, fluorine gas or chlorine gas into at least one location between the SiO generator and the SiO condenser and reacting with P contained in the SiO gas is preferable.

  A method in which the gas temperature of the SiO gas retainer is in the range of 1200 ° C. or more and 2000 ° C. or less is preferable.

  A method in which the average gas residence time in the SiO gas retainer is 0.1 seconds or more is preferable.

  Furthermore, the present invention relates to a method for producing high-purity Si, characterized by using the SiO obtained above as a raw material.

  According to the device of the present invention and the method using such a device, impurities P contained in SiO can be greatly reduced.

  Further, by using such purified SiO, high purity Si can be easily produced.

The present inventors, when holding a single P gas evaporated when SiO generated changes to _P 2, _{P 4} gas, such _P 2, _{P 4} gas was discovered phenomenon hardly adsorbed to the condensation SiO. Based on this knowledge, the form of the vaporized simple substance P in the gas phase can be changed easily and efficiently, and an inexpensive SiO refining device with a low P concentration, a method for purifying SiO, and a high-performance material using such purified SiO as a raw material. A method for producing pure Si has been devised.

  In the following, the description will be divided into SiO purification and Si production methods. In the present specification, the phenomenon in which the SiO gas is solidified in the condenser is referred to as condensation.

(Purification of SiO)
FIG. 1 is a schematic sectional view showing an example of an apparatus used for purifying SiO. In FIG. 1, a Si particle-SiO ₂ particle mixed raw material 5 previously installed in a crucible 3 in a reaction vessel 1 is heated by a heating device 7 disposed around the crucible 3. The reaction vessel 1 is connected to a condenser 11 through a stayer 9. Here, the retainer 9 includes a plurality of baffle plates 13 inside, and is kept warm by a heating device (not shown) from the outside. Further, the inside of the reaction vessel 1, the retainer 9 and the condenser 11 is maintained at a low pressure by the vacuum pump 15 and is monitored by the pressure gauge 17. When the raw material temperature rises sufficiently, the SiO gas 19 is generated by the reaction (3), and the impurity P in the SiO is changed into a form in which it is difficult to be adsorbed by the condensed SiO in the retainer 9 and then flows into the condenser 11. The outer wall of the condenser 11 is cooled, and SiO solidifies and adheres to the plate surface to form a SiO solid 21. The flow path in the condenser 11 is set long enough to recover most of the SiO as a condensate.

  FIG. 2 is a schematic cross-sectional view showing another example of an apparatus used for purifying SiO. In FIG. 2, a gas mixer 35 having a blowing gas cylinder 31 and a carrier gas cylinder 33 is further attached to the apparatus shown in FIG. 1. The gas mixer 35 is connected to the blow-in gas cylinder 31 via the first flow rate adjustment valve 39, is connected to the carrier gas cylinder 33 via the second flow rate adjustment valve 41, and is further connected to the reaction vessel via the third flow rate adjustment valve 43. 1 is connected. A preheater 37 is attached to the gas mixer 35 so that the gas can be preheated if necessary.

Here, the SiO generator or the reaction vessel can be used without particular limitation as long as it is a device that generates SiO gas from a mixture of Si and SiO ₂ . Examples of such an apparatus include a crucible and a reaction vessel provided therein with a heating device for heating a crucible provided around the crucible. A conventionally well-known apparatus can be used for this crucible and a heating apparatus. The reaction vessel guides the generated SiO gas to the next condenser without leaking outside. Therefore, the shape is usually an L shape rotated by 180 degrees in the front view. The reaction vessel generates a SiO gas by heating a mixture of Si particles and SiO ₂ particles and leads it to the next condenser, so that the temperature at which the SiO gas does not condense on the inner wall, for example, a temperature exceeding 1100 ° C., It is preferable to maintain the temperature in the range of more than 1100 ° C. and 2000 ° C. or less.

If the simple substance P gas which evaporates when SiO is generated is maintained for a sufficient time, the P gas is converted into P ₂ or P ₄ gas. Such gas has little adsorption to condensed SiO. Therefore, a retention device is provided between the reaction vessel and the condenser so that a sufficient holding time can be obtained. The retainer may be a simple cavity, but it is too large and requires a large space. A plurality of plates or baffle plates were provided in the SiO gas flow path, the plate surface was directed in the gas flow direction, and alternately provided at regular intervals from the facing surface forming the flow path, and the gas flow was configured to be zigzag. A container through which gas can pass can be used as a retainer. If such a retainer is used, it can be used even in a narrow place. In addition, the retention device extends the residence time of the SiO gas, but since it is not necessary to attach SiO, a heating device (not shown) that keeps the retention device warm so that SiO does not adhere to the wall surface or baffle plate. ).

  The condenser is a container whose purpose is to collect SiO gas as a solid by condensation. Normally, a plurality of plates or baffle plates are provided in the SiO gas flow path, the plate surface is directed in the gas flow direction, and alternately provided at predetermined intervals from the facing surface forming the flow path so that the gas flow is zigzag. In addition, a container through which gas can pass or an empty container can be mentioned. The interval is usually constant, and in order to increase the recovery efficiency, the upstream side of the SiO gas having a high SiO density may be shortened and the downstream side may be lengthened. The temperature of the condenser is not particularly limited as long as SiO gas can be condensed.

Next, a method for purifying SiO will be described. SiO gas is generated using a mixture of Si and SiO ₂ as a raw material. As Si and SiO ₂ , conventionally used Si metal grains and silica sand can be used. For example, as Si metal, P is 80 ppm, B is 9 ppm, Fe is 1500 ppm, other metal components are 500 ppm, and impurities in high-purity silica sand are P of 0.3 ppm, B of 0.5 ppm, Fe Is 400 ppm, and other metals are about 100 ppm.

A mixture of Si and SiO ₂ is put into a crucible as a raw material, and the inside of the reaction vessel is replaced with an inert gas such as Ar, He, or CO ₂ gas.

  The raw material is heated by a heating device, for example, a resistance heater, provided around the crucible, and the inside of the reaction vessel is maintained at a predetermined pressure reduction level by operating a vacuum pump.

  The raw material is heated to, for example, 1700 ° C., and a vacuum pump provided at the rear or rear of the condenser is operated to bring the inside of the reaction vessel to a predetermined pressure, for example, 10 Pa. It should be noted that when the raw material temperature exceeds a predetermined temperature, for example, 1410 ° C., the generation amount of SiO gas increases rapidly and the pressure in the reaction vessel also increases rapidly.

  The generated SiO gas is led from the reaction vessel to the staying device. At this time, a part of P contained in Si is also evaporated. In the Si melt, P is said to exist stably in a single atom state. For this reason, in particular, when the P concentration is several tens of ppm or less, the vaporized P gas is mainly composed of monoatomic P molecules. On the other hand, it is considered that the vaporized P vapor undergoes the following reaction in the retainer that is in the gas phase.

nP (gas) = Pn (gas)
However, in formula, n is an integer of 2-4.

This equilibrium is high in the ratio of the polymer gas on the right side under the temperature and pressure conditions of the operation of generating SiO. Therefore, the higher the P concentration in SiO, the higher the ratio of Pn. If the simple substance P gas which evaporates at the time of SiO generation is held for a sufficient time inside the staying vessel, the simple substance P gas in the SiO gas is reduced to a ratio corresponding to the amount of P ₂ and P ₄ gas in the equilibrium state. Here, the P ₂ and P ₄ gases have a characteristic that they are less likely to be adsorbed to the condensed SiO than the simple substance P gas. That is, SiO gas can be retained in the retention device, and P molecules can collide and bond with each other during the retention, thereby effectively increasing P ₂ and P ₄ .

  The stayer is intended only to reduce the single substance P, and it is not necessary to condense the SiO gas. Therefore, the stayer needs to be maintained at a temperature at which SiO does not condense. The temperature is maintained using a heating device. The heating device needs to be maintained at a temperature at which SiO gas does not condense on the inner wall or baffle plate of the device, for example, a temperature exceeding 1100 ° C., preferably in the range of 1200 to 2000 ° C. This is because below this temperature, SiO is condensed inside the retainer and the yield is greatly reduced. If necessary, a heating device may be provided in the baffle plate to improve the prevention efficiency of SiO condensation.

  Further, the residence time in the SiO gas retainer is not particularly limited as long as the simple substance P decreases, but usually a residence time of 0.1 seconds or more, preferably 0.1 seconds to 1 hour is provided. Is desirable. This is because when the residence time is less than 0.1 second, the effect of improving the obtained SiO purity is not recognized.

  After the single substance P in the generated SiO gas is retained and processed, the outside is condensed by a condenser cooled with a refrigerant such as water or air to form a solid SiO film. In order to increase the condensation efficiency, a refrigerant may be passed through the baffle plate. Since the temperature of the condenser is intended to recover the SiO gas, the temperature at which the SiO gas can be condensed on the baffle plate and does not condense the low boiling point compounding portion, for example, 1100 ° C. or less, preferably It is desirable that the temperature be in the range of 1100 ° C to 110 ° C. The pressure in the condenser at this time is maintained at a predetermined value, for example, 400 Pa. The residence time of the SiO gas in the condenser is not particularly limited as long as SiO is sufficiently adhered to the baffle plate.

  Next, SiO adhering to the condenser is recovered. As a recovery method, a conventionally used method can be adopted. For example, the entire condenser is cooled, and the solid SiO is peeled off from the baffle plate of the disassembled container and recovered.

  Since phosphorus contained in the SiO gas has changed into a form in which it is difficult to adsorb with condensed SiO, phosphorus does not substantially adhere to the condenser. That is, it passes through the condenser.

  In addition to the above method, the following method may be mentioned as a method for making it difficult to adsorb P contained in the SiO gas to the condensed SiO.

  A gas that reacts with phosphorus contained in the SiO gas to form a low boiling point compound is introduced into the reaction vessel. In addition, since the inside of the reaction vessel is usually maintained at a reduced pressure, the low boiling point compound forming gas can be introduced using the differential pressure, but can be effectively dispersed by blowing the gas. The low boiling point forming gas is not particularly limited as long as it is a gas capable of forming a low boiling point compound by reacting with phosphorus contained in SiO gas in a gas phase, for example, hydrogen gas, fluorine gas or chlorine gas. Is mentioned.

  When hydrogen gas is blown into the reaction vessel, hydrogen and P are considered to react as follows.

P (gas) + nH ₂ (gas) → phosphorus hydride [PHm] (gas) (7)
However, in formula, m is an integer of 1-4.

The produced phosphorus hydride is a low boiling point compound having a boiling point of about 60 ° C. or less, and has a property of being hardly adsorbed on SiO. For example, the boiling point of PH ₃ is −87 ° C. and the boiling point of P ₂ H ₄ is 51.7 ° C. (Revised 3rd edition, Chemical Handbook, Basics I, The Chemical Society of Japan, Maruzen Co., Ltd.).

However, the hydrogen gas also reacts with the SiO gas, and silicon hydride gases such as SiH ₄ and Si ₂ H ₆ are generated at the same time. Such silicon hydride need not take into account the effect on the quality of SiO. This is because the reaction for forming silicon hydride is slower than the formula (7), and the amount of silicon hydride generated is small. Further, since silicon hydride has a low boiling point and has a property of being less adsorbed on condensed SiO, most of it is exhausted out of the system together with phosphorus hydride. For example, the boiling point of SiH ₄ is -111.8 ° C., and the boiling point of Si ₂ H ₆ is −14.5 ° C. (Revised 3rd edition, Chemical Handbook). Further, most of the hydrogen remaining in the SiO is removed in a subsequent process (Si extraction process).

  When fluorine gas is blown into the reaction vessel, fluorine and P are considered to react as follows.

P (gas) + nF ₂ (gas) → phosphorus fluoride [PFm] (gas) (8)
However, in formula, m is an integer of 1-5.

The produced phosphorus fluoride is a low boiling point compound having a boiling point of 0 ° C. or less, and has a property of being less adsorbed on condensed SiO. For example, PF _{3 has} a boiling point of −101.5 ° C. and PF _{5 has} a boiling point of −75 ° C. (Revised 3rd edition, Chemical Handbook).

However, fluorine gas also reacts with SiO gas, and silicon fluoride gas such as SiF ₄ is generated at the same time. Such silicon fluoride gas need not take into account the effect on the quality of SiO. This is because the reaction for forming silicon fluoride is slower than the formula (8), and the amount of silicon fluoride generated itself is small.

  When chlorine gas is blown into the reaction vessel, chlorine and P are considered to react as follows.

P (gas) + nCl ₂ (gas) → phosphorus chloride [PClm] (gas) (9)
However, in formula, m is an integer of 1-5.

The produced phosphorus chloride is a low boiling point compound having a boiling point of about 100 ° C. or less and has a characteristic that it is hardly adsorbed onto SiO. For example, the boiling point of PCl ₃ : 75.5 ° C, the boiling point of PCl ₅ : sublimation 100 ° C (3rd revised edition, Chemical Handbook).

However, chlorine gas also reacts with SiO gas, and silicon chloride gas such as SiCl ₄ is generated at the same time. The effect of silicon chloride on the quality of SiO need not be considered. This is because the reaction for forming silicon chloride is slower than the formula (9), and the amount of generated silicon chloride itself is small.

  Representative examples of the low boiling point forming gas include hydrogen gas, fluorine gas, and chlorine gas. However, when these gases are mixed and introduced into the reaction vessel, these gases may react with each other. These gases are desirably used alone without being mixed. Of these, hydrogen gas is preferred from the viewpoint of the corrosion resistance of the reaction vessel.

The amount of the low boiling point forming gas introduced is not limited as long as impurities such as P contained in the raw materials Si and SiO ₂ can be completely converted into low boiling point compounds. Usually, the introduction amount of the low boiling point forming gas is in the range of the theoretical amount reacting with the impurity P present in the SiO to 50 mol% or less of the generated SiO. Here, the theoretical amount corresponds to a reaction that generates the simplest compound, for example, a reaction based on a reaction that generates PH _{3 in} the case of hydrogen gas, PF _{3 in} the case of fluorine gas, and PCl _{3 in} the case of chlorine gas. . If the amount is less than the theoretical amount, formation of a low boiling point compound is not sufficient, and on the other hand, the low boiling point forming gas reacts with SiO, so that it is not preferable to exceed 50 mol% of generated SiO.

  The introduction point of the low boiling point forming gas is not particularly limited as long as it is upstream of the SiO gas retaining device. Further, when there is a design restriction, the low boiling point forming gas may be introduced in the vicinity of the SiO gas inlet in the SiO gas retaining device. With such an arrangement, the low boiling point forming gas can be efficiently supplied into the SiO gas retaining device.

As a method for introducing the low boiling point forming gas, 1) a method from a gas cylinder through a flow rate adjusting valve, 2) a carrier such as Ar, CO ₂ gas, and He having low reactivity in the furnace once. The method of mixing with gas can be mentioned. In the case of 1), there is an advantage that the reaction rate and reaction rate are high in the local area of the SiO gas, but since the amount of blown gas is small, mixing with the SiO gas tends to be local and unreacted sites are likely to occur. , Have the disadvantages. In the case of 2), the amount of introduced gas is large, and there is an advantage that the mixing with SiO gas and the reaction can be made uniform, but on the other hand, there are disadvantages in that the reaction rate and reaction rate in the SiO gas local area are low. Both have advantages and disadvantages, but 2) is preferred from the standpoint of uniform mixing and reaction with SiO gas.

  Since the low-boiling point gas is reacted with phosphorus contained in the SiO gas to form a low-boiling point compound, phosphorus does not substantially adhere to the condenser. Further, the low boiling point forming gas, the reaction product of SiO and the low boiling point forming gas, and the non-condensable gas such as carrier gas pass through the condenser without being condensed.

  P, which is an impurity in SiO, can be greatly reduced by a simple means of retaining gas by providing a retention vessel between the reaction vessel and the condenser.

(Manufacture of Si)
A conventionally known method can be adopted for extracting Si from SiO. For example, the SiO obtained above is put into a crucible, for example, a high-purity graphite crucible, and the whole crucible is charged into a heating furnace. The SiO is heated at atmospheric pressure and in an inert gas atmosphere, for example, Ar, CO ₂ gas, He, a predetermined temperature, for example, 1550 ° C. for a predetermined time, for example, 1 hour, and then cooled and solidified. Thereafter, it is taken out of the furnace. Since the processing time varies depending on the size of the heating furnace and the amount of SiO to be processed, it can be appropriately changed.

Most of SiO is in a state of being separated into two phases of Si and SiO ₂ due to the disproportionation reaction, and Si is obtained by peeling the SiO ₂ grains from the Si lump. By removing impurities in the SiO raw material according to the present invention, the component specifications of Si for solar cell substrates can be satisfied even if inexpensive Si containing a high concentration of P is used as the raw material.

  Here, the component specification of Si for solar cell substrates refers to the following composition. In general, it is said that the higher the purity of Si for solar cell substrate, the higher the performance, but the performance improvement rate gradually decreases as the purity increases. On the other hand, the higher the purity of Si, the more rapidly the cost for increasing the purity, so a certain Si purity is the cost-effective optimum. This optimum point differs for each component, and it is desirable to use Si in the following range in order to satisfy the performance having market value as the present solar cell. That is, phosphorus (P) 0.1 ppm or less in mass ratio, arsenic (As) 0.1 ppm, antimony (Sb) 0.1 ppm or less, boron (B) 0.3 ppm or less, gallium (Ga) 0.1 ppm or less, indium (In) 0.1 ppm or less and other metal components 0.1 ppm or less.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples.

(Example 1)
1. Purification of SiO Production and purification of SiO were performed according to the apparatus shown in FIG.

  A crucible having a diameter of 0.5 m was placed in a reaction container having a diameter of 1 m, and a mixture of 40 kg of metal Si and 150 kg of high-purity silica sand was put therein. At this time, the average diameter of the grains was 0.4 mm for metal Si and 7 mm for silica sand. Further, the impurities of metal Si are 80 ppm for P, 9 ppm for B, 1500 ppm for Fe, and 500 ppm for other metal components, and the impurities in high-purity silica sand are all 0.3 ppm for P and 0. 5 ppm, Fe 400 ppm, and other metals 100 ppm.

  Next, the inside of the reaction furnace was filled with argon (Ar) gas, and the raw material was heated to 1700 ° C. with a resistance heater installed around the crucible, and the pressure inside the reaction vessel was adjusted to 10 Pa by operating the vacuum pump. When the raw material temperature exceeded 1410 ° C., the generation of SiO gas rapidly increased, and the pressure in the reaction vessel finally reached 1300 Pa.

  A reservoir is provided between the reaction vessel and the condenser. The retainer is a 2m square box-type container. By arranging a baffle plate inside, the SiO gas flow shortcut is prevented and the pressure in the upstream part of the condenser is maintained at a high value close to the internal pressure of the reaction container. In this case, the residence time of the SiO gas is extended. As the material of the retainer, the inner surface was pasted with high purity graphite. In addition, an electric heater was installed outside the stayer in order to keep the internal temperature at 1400 ° C. The average residence time of the SiO gas was 1 second.

  The generated SiO gas was solidified on the inner wall of the condenser whose outside was water-cooled to form a solid SiO film. The condenser internal pressure at this time was 400 Pa on average. After the heating operation at 1700 ° C. was continued for 1.5 hours, the apparatus was cooled, and the solid SiO was peeled off from the disassembled condenser inner wall and recovered. The metal Si remaining in the crucible was 0.06 kg, and the solid SiO exfoliated and recovered from the condenser was about 160 kg. The SiO raw material temperature was measured with a thermocouple attached to the inner wall of the crucible, and the pressure was measured with a non-contact type pressure gauge for the pressure inside the heat insulating tube drawn out of the container. As a result of component analysis in the obtained solid SiO, P was 0.4 ppm, B was 0.3 ppm, Fe was 0.07 ppm, and other metal components were 1 ppm in total.

The removal rate of P by this method was 99.5%.
2. Production of Si from SiO Next, Si was extracted from SiO in the Si extraction step. The SiO obtained above was put into a crucible made of high purity graphite, and the whole crucible was charged into a heating furnace. This SiO was heated at 1550 ° C. under an atmospheric pressure argon atmosphere for 1 hour, then cooled and solidified, and taken out of the furnace. Most of the SiO charged at this stage is separated into two phases of Si and SiO ₂ due to the disproportionation reaction. The SiO ₂ particles are peeled off from the Si lump by hand to obtain 25 kg of Si. It was. As a result of component analysis of a part of this Si, P was 0.4 ppm, B was 0.23 ppm, Fe was 0.08 ppm, H was 0.1 ppm, and other metal components were 0.01 ppm.

1 kg of the obtained Si is mixed with 3 kg of semiconductor scrap Si, which is the current Si raw material for solar cell substrates, and the impurities are diluted to satisfy the component tolerance as high-purity Si for solar cell substrates. was gotten. Further, in order to apply the obtained Si alone to high-purity Si for solar cell substrates, the remaining Si obtained was melted and subjected to vacuum degassing treatment. This is an application of the conventional technique of improving the purity by evaporating impurities in Si by melting commercial metal Si and exposing it under vacuum. However, as in this example, there was no precedent in which vacuum degassing treatment was performed on Si obtained from SiO. Unlike the case of using metal Si, it is inevitable that a very small amount of SiO ₂ particles are dispersed in the Si phase, although the amount is small in Si obtained from SiO. There is no knowledge about the influence of fine SiO ₂ grains on the vapor pressure of P in the Si liquid phase. Therefore, it is not obvious whether the conventional vacuum degassing technique is effective for the Si obtained in this example. The vacuum degassing process in this example was performed under the following conditions. First, Si which was crushed and formed into a lump having a diameter of about 10 mm was placed in a high-purity graphite crucible having a diameter of 0.35 m and placed in a vacuum heating furnace. The inside of the heating furnace was made into a weakly oxidizing atmosphere of 0.1 Pa, the Si lump was heated and melted, and the temperature of the Si solution was raised between 1600 ° C. and then kept under vacuum for 1 hour. After cooling Si, it took out from the furnace, and as a result of component analysis, what satisfy | filled the required component value of the high purity Si for solar cell substrates was obtained.

  When there is no retainer under the same production conditions, the average P concentration in SiO is 5 ppm, which means that the P concentration in SiO can be reduced by one digit or more, greatly reducing the subsequent vacuum degassing process load. did it.

  In this method, since gas blowing is not performed, there is an advantage that it is not necessary to consider the contamination by the blowing gas and the facilities are simplified.

(Example 2: Hydrogen gas blowing)
1. Purification of SiO Production and purification of SiO were performed according to the apparatus shown in FIG. Hydrogen gas was used as the blowing gas and Ar gas was used as the carrier gas, and was blown from the top of the SiO generator.

  A crucible having a diameter of 0.5 m was placed in a reaction container having a diameter of 1 m, and a mixture of 40 kg of metal Si and 150 kg of high-purity silica sand was put therein. At this time, the average particle diameter was 0.4 mm for metal Si and 7 mm for silica sand. Further, impurities of metal Si are 80 ppm for P, 9 ppm for B, 1500 ppm for Fe, and 500 ppm for other metal components, and all impurities in high-purity silica sand are 0.3 ppm for P and 0. 5 ppm, Fe 400 ppm, and other metals 100 ppm.

  Next, the inside of the reaction furnace was filled with argon (Ar) gas, and the raw material was heated to 1700 ° C. with a resistance heater installed around the crucible, and the pressure inside the reaction vessel was adjusted to 10 Pa by operating the vacuum pump. During the purification of SiO, hydrogen gas 1 mg / s and Ar gas 10 mg / s were always mixed, preheated to 1200 ° C., and then continued to be blown into the reactor. When the raw material temperature exceeded 1410 ° C., the generation of SiO gas rapidly increased, and the pressure in the reaction vessel finally reached 1300 Pa.

  The generated SiO gas was solidified on the inner wall of the condenser whose outside was water-cooled to form a solid SiO film. The condenser internal pressure at this time was 400 Pa on average. After the heating operation at 1700 ° C. was continued for 1.5 hours, the apparatus was cooled, and the solid SiO was peeled off from the disassembled condenser inner wall and recovered. The metal Si remaining in the crucible was 0.06 kg, and the solid SiO exfoliated and recovered from the condenser was about 160 kg. As a result of component analysis in the obtained solid SiO, P was 0.04 ppm, B was 0.3 ppm, Fe was 0.07 ppm, and other metal components were 1 ppm in total.

The removal rate of P by this method was 99.95%.
2. Production of Si from SiO Next, Si was extracted from SiO in the Si extraction step. The SiO obtained above was put into a crucible made of high purity graphite, and the whole crucible was charged into a heating furnace. This SiO was heated at 1550 ° C. under an atmospheric pressure argon atmosphere for 1 hour, then cooled and solidified, and taken out of the furnace. Most of the SiO charged at this stage is separated into two phases of Si and SiO ₂ due to the disproportionation reaction. The SiO ₂ particles are peeled off from the Si lump by hand to obtain 25 kg of Si. It was. As a result of component analysis of a part of this Si, P was 0.04 ppm, B was 0.23 ppm, Fe was 0.08 ppm, H was 0.1 ppm, and other metal components were 0.01 ppm. The obtained Si satisfied the component specifications of Si for solar cell substrates.

It is the schematic explaining an example of the apparatus for SiO manufacture of this invention. It is the schematic explaining the other example of the apparatus for SiO manufacture of this invention.

Explanation of symbols

1 reaction vessel,
5 Si grain-SiO ₂ grain mixed raw material,
3 crucible,
7 Heating device,
9 Retainer,
11 Condenser,
13 baffle,
15 vacuum pump,
17 Pressure gauge,
19 SiO gas,
21 solid SiO,
23 Impurity vapor,
31 Blowing gas cylinder,
33 Carrier gas cylinder,
35 gas mixer,
37 Preheater,
39, 41, 43 Flow control valve.

Claims (7)

  A SiO refining device comprising a SiO gas retention device between a SiO generator and a SiO condenser.   A method for purifying SiO, comprising using the apparatus according to claim 1. The method according to claim 2, wherein the P gas concentration in the condensed SiO is reduced by setting the P vapor in SiO to P ₂ or P _{4 in the} SiO gas retainer.   The method according to claim 2 or 3, wherein hydrogen gas, fluorine gas, or chlorine gas is introduced into at least one location between the SiO generator and the SiO condenser to react with P contained in the SiO gas.   The method according to any one of claims 2 to 4, wherein a gas temperature of the SiO gas retainer is set in a range of 1200 ° C or higher and 2000 ° C or lower.   The method according to any one of claims 2 to 5, wherein an average gas residence time in the SiO gas retainer is 0.1 seconds or more.   A method for producing high-purity Si, characterized in that SiO obtained by the method according to any one of claims 2 to 6 is used as a raw material.

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