JP2005225729A - PURIFYING APPARATUS OF SiO, PURIFYING METHOD OF SiO USING THE SAME AND MANUFACTURING METHOD OF HIGH PURIFIED SILICON - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purifying apparatus of SiO with the low P concentration from a SiO raw material with the high P concentration, and to provide a manufacturing method of a high purified Si using such a purified SiO. <P>SOLUTION: The purifying apparatus is a SiO purifying apparatus containing a SiO generator, a first SiO condenser and an displacement pump. The purifying apparatus is characterized by arranging a second SiO condenser between the first SiO condenser and the displacement pump. The purifying method uses such a apparatus. The manufacturing method of the high purified Si uses the purified SiO. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus for purifying SiO, a method for purifying SiO using such an apparatus, and a method for producing high-purity silicon, and more particularly, to a method for producing high-purity silicon that can be used for solar cells.

  Si used for the solar cell substrate is required to have an extremely high purity of 99.9999% or more (hereinafter referred to as "high purity Si"), and a lower purity than this. Hereinafter referred to as “low purity Si”). In particular, impurity elements in Si that adversely affect battery performance are phosphorus, arsenic, antimony, boron, gallium, and indium, which are called n-type impurity elements or p-type impurity elements that significantly reduce the electromotive force generated by sunlight. In addition, other metal elements that lower the electrical resistance to inhibit the insulation of the element or inhibit the movement of electric charges generated in the battery, such as iron, aluminum, nickel, titanium, and the like. 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.

  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 impurities in the final Si product are well investigated for many elements, interest in impurities in SiO is low, and only a small number of components such as Fe, Al, and P are present. However, it has only been investigated and disclosed. 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, 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.

  Further, it is required to efficiently recover the condensable material discharged from the SiO recovery device.

  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.

  Therefore, 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 and a purification method using such an apparatus.

  Another 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 including a SiO generator, a first SiO condenser, and an exhaust pump, wherein a second SiO condenser is disposed between the first SiO condenser and the exhaust pump. It is related with the refinement | purification apparatus characterized by these.

  The present invention also relates to a method for purifying SiO, characterized by using the above-described purification apparatus.

  A method of flowing SiO gas into the second SiO condenser at a rate of 0.1% or more of the SiO generation rate is preferable.

  A method of setting the gas temperature inside the second condenser to be lower than the gas temperature inside the first condenser is preferable.

  A method in which the condensation surface temperature of the second condenser is 100 ° C. or less is preferable.

  Furthermore, this invention relates to the manufacturing method of high purity Si characterized by using refined SiO obtained by the said method.

  According to the SiO purification apparatus of the present invention and the purification method using such a purification apparatus, the raw material yield at the time of SiO purification can be greatly improved, and a vacuum pump with a smaller capacity can be provided. Can be greatly reduced.

  According to the high purity Si production method of the present invention, high purity Si can be easily obtained by using the purified SiO obtained above as a raw material.

  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)
The SiO purification apparatus of this invention is demonstrated based on drawing. FIG. 1 is a schematic drawing showing an example of an SiO purification apparatus. 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. Further, the inside of the reaction vessel 1, the first condenser 11 and the second condenser 15 is maintained at a low pressure by the vacuum pump 9 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 flows into the first condenser 11. The outer wall of the first condenser 11 is cooled, and as a result, SiO solidifies and adheres to the plate surface to form a SiO solid 21. The flow path in the first condenser 11 is set sufficiently long, and most of the SiO is recovered as a condensate. A second condenser 15 is connected after the first condenser 11. Further, a vacuum pump 9 is provided at the rear or rear of the second condenser 15. The second condenser 15 condenses and collects the SiO that has passed through the first condenser 11 and collects impurity vapor 23 of a low-boiling point substance such as P contained in a large amount in the SiO raw material. To the condenser 15 as deposit 25.

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 equipped with a crucible heating device provided around the crucible. A conventionally well-known apparatus is 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 desirable to maintain the temperature in the range of more than 1100 ° C. and 2000 ° C. or less.

  The first condenser is not particularly limited as long as SiO gas can be condensed and deposited and recovered as a SiO solid. 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 the SiO gas can be condensed, but the SiO gas can be effectively condensed by cooling the first condenser. Since the purpose is to recover the SiO gas, the temperature at which the SiO gas can be condensed is, for example, 1100 ° C. or lower, preferably 1100 ° C. to 100 ° C.

  The second condenser may be of the same type as the first condenser, but it condenses the condensable material from the gas after most of the target SiO has already been recovered, so it may be different. Good. For example, when the first condenser uses a container configured such that the gas flow is zigzag as described above, an empty container is used as the second condenser. Similarly, as the first and second condensers, an empty container may be used, the first condenser may be air-cooled, and the second condenser may be water-cooled. The temperature of the second condenser is not particularly limited as long as unrecovered SiO gas and impurities P can be condensed. However, it is preferable to effectively condense the SiO gas by cooling the second condenser. . Since the purpose is to condense SiO gas and the like, the temperature at which SiO gas can be condensed and impurities P and the like can be condensed, for example, less than 100 ° C., preferably less than 100 ° C. to −50 It is desirable that the temperature be in the range of ° C, more preferably less than 100 ° C to room temperature. By adopting such a combination of condensers, it is possible to condense condensable substances such as SiO and P which is an impurity without overloading the vacuum pump.

  As the vacuum pump, a conventionally known pump can be used without particular limitation as long as the inside of the reaction vessel and the first and second condensers can be maintained in a reduced pressure state.

  Here, the reason why the condenser is divided into the first and the second will be described. In SiO refining, when SiO gas is generated from the reaction vessel, P contained in the raw material is also released as a large amount of vapor. P vapor flows into the condenser together with the SiO gas. In the condenser, SiO is condensed to form a solid surface, and this SiO solid surface has a property of efficiently adsorbing P vapor. For this reason, when the total amount of the generated SiO gas is condensed and recovered, the average concentration of P in the SiO solid is as high as that of the raw material Si, which is a problem in terms of quality. Furthermore, as the SiO condensed downstream, the P concentration in SiO is higher. These phenomena have been found by the present inventors. Therefore, if the SiO gas downstream of the condenser is discharged outside the condenser without being condensed, the P concentration in the SiO gas condensed in the condenser becomes the average P concentration when all the generated SiO is condensed. Compared to this, it can be greatly reduced.

  When such work is performed, if the SiO gas downstream of the condenser is exhausted through the vacuum pump as it is, the following problems occur. First, in order to perform this operation, it is necessary to provide a large-capacity vacuum pump, which requires extra equipment costs. This is because when the entire amount of SiO gas is condensed in the condenser, only a small amount of non-condensable gas should be discharged out of the system by a vacuum pump, whereas a part of the SiO gas is exhausted. This is because, for example, a large amount of exhaust of several percent of the amount of generated SiO gas must be performed. Second, the maintenance load of the vacuum pump increases. This is because the flow path of the vacuum pump and the surface of the blades are rotating machines, so it is difficult to maintain at a high temperature in terms of material (to maintain a high temperature, an expensive pump material must be used, Not realistic.) For this reason, when SiO gas passes a low-temperature vacuum pump wall surface, a part of SiO gas condenses within the vacuum pump and adheres to the vacuum pump wall surface. As a result, if the work is continued for a certain time or longer, the phenomenon that the blades of the vacuum pump cannot be rotated due to the SiO condensate or the vacuum pump flow path is blocked, making it difficult to continue the work. This is because the vacuum pump must be replaced and serviced.

  It seems that these problems can be solved at a glance by condensing the entire amount of SiO gas in a single condenser and recovering only high-purity sites from the condensed SiO. However, the temperature, pressure distribution in the condenser, and the SiO condensation rate distribution inside the condenser change every moment during the operation. This is because the SiO condensate continuously grows on the condenser wall inside the condenser, and the operating conditions on the SiO generator side often fluctuate during the operation. Therefore, it is practically difficult to make a strict judgment as to which part of the finally obtained SiO solid is recovered in order to recover quality only. When such work is selected, it is necessary to discard a large proportion of the condensed SiO solids, such as several tens of percent, in view of quality safety, avoiding a large drop in yield. I can't.

  Therefore, in the present invention, the first and second condensers are divided into two, and each is made to have completely different working conditions, so that in the first condenser, higher purity SiO is condensed and recovered. In the second condenser, the remaining low-purity SiO gas is condensed entirely. Here, the concept of the method for setting the working conditions of each condenser will be described.

  In the present invention, it is easy to greatly change the working conditions between the two condensers. Therefore, for example, a high temperature working condition, for example, 500 ° C. is set so that the first condenser can be sent to the second condenser without always condensing a certain amount of SiO gas. Thus, the second condenser is maintained at a low-temperature working condition near normal temperature. Alternatively, a flow control valve is installed between the first and second condensers, and this flow control valve is operated so that the indicated value of the pressure gauge installed in the first condenser is always a constant value. Thus, the first condenser may always be sent to the second condenser without condensing a certain amount or more of the SiO gas. By setting such a condition, a relatively small amount of lower purity SiO can always be condensed only in the second condenser, and only a relatively small amount of non-condensable gas in which no SiO gas remains. Can be evacuated through a vacuum pump. As a result, it is possible to avoid a large yield drop as in the case of manufacturing SiO using a single condenser, to reduce the capacity of the vacuum pump, and to further reduce the maintenance load of the vacuum pump. be able to. As described above, it is easy in the present invention to suddenly change the working conditions such as temperature and pressure in the longitudinal direction of the flow in the condenser, but it is difficult when there is only one condenser.

Next, a method for purifying SiO will be described. As a method for purifying SiO, any method can be used without particular limitation as long as it is a method for obtaining SiO from a mixed raw material of Si and SiO ₂ .

  Reaction in the contact surface between both materials of 3000 Pa or less in a temperature range of 1400 ° C. to 1800 ° C. after laminating a mixture of silicon containing impurities of 1 ppm or more and a solid material mainly composed of silicon dioxide in a reaction vessel The silicon monoxide gas is generated by the above, and the gas is further cooled to solidify part of the silicon monoxide and then recovered by the first condenser, and the other silicon monoxide is condensed by the second condenser. Method.

In the SiO purification method, the apparatus shown in FIG. 1 is used to generate SiO gas 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 40 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 sufficiently dissolved and heated to, for example, 1700 ° C., and the vacuum pump provided at the rear of the second condenser is operated to set 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 condensed by a first condenser having the inside cooled with a refrigerant such as air and formed into a solid SiO film. A desirable range of the working temperature of the first condenser will be described. For the purpose of recovering SiO, the first condenser needs to be at a temperature at which SiO can condense on the SiO condensation surface, for example, 1100 ° C. or lower. Further, as a result of investigation by the present inventor, it has been found that a suitable operation cannot be performed unless the condensing surface temperature of the first condenser is higher than the condensing surface temperature of the second condenser. That is, when the condensation surface temperature of the second condenser is higher than the condensation surface temperature of the first condenser and the SiO gas generation pressure is low, all of the generated SiO gas is condensed in the first condenser. On the other hand, when the SiO gas generation pressure is high, there arises a problem that the entire amount of SiO gas cannot be condensed in the second condenser. Further, the present inventor has found that when the condensing surface temperature of the second condenser is 100 ° C. or less, the SiO flowing into the second condenser is easily condensed. From this result, the suitable temperature range of the second condenser condensing surface is 100 ° C. or less, and the condensing surface temperature of the second condenser may be about 100 ° C. in some cases. For this reason, in the first and second condensers cooled from the outside of the condenser, the gas temperature inside the condenser is generally higher than the condensation surface temperature, so that it is higher than the condensation surface temperature of the second condenser. In order to do this, the gas temperature immediately before the outflow in the first condenser needs to be at least over 100 ° C., and in order to keep this gas temperature condition, the first condenser that cools the gas in the first condenser The condensation surface must be at this temperature as a minimum. That is, the condensation surface temperature of the first condenser needs to exceed 100 ° C. Further, the present inventors have found that when the condensation surface temperature is less than 500 ° C., the adsorptivity of P vapor to the SiO solid surface is enhanced. For this reason, in order to obtain the required purity SiO when the condensation surface temperature is less than 500 ° C., it is necessary to condense more SiO gas in the second condenser (that is, the yield decreases), The inventor found. Therefore, a more desirable condition of the condensation surface temperature of the first condenser is in the range of 500 to 1100 ° C. At this time, the pressure in the first condenser is maintained at a predetermined value, for example, 400 Pa. The residence time of the SiO gas in the first condenser is not particularly limited as long as SiO is sufficiently deposited.

  The second condenser is an empty container in the water-cooled type. Here, it is desirable to allow SiO gas to flow into the second condenser at a mass ratio of usually 0.1% or more, preferably 0.1 to 50% of the generation rate of SiO. Here, the basis of the limit value of this work condition will be described. First, the lower limit of the mass ratio of the SiO gas flowing into the second condenser with respect to the SiO generation rate will be described. According to the investigation by the present inventor, when a gas amount less than 0.1% (mass ratio) of the SiO generation rate is caused to flow into the second condenser, a large proportion of these gases is in the second condenser. It flowed into the vacuum pump without condensing inside and condensed on the wall surface of the vacuum pump. The reason for this phenomenon is as follows. Since the temperature in the second condenser is generally set to a low temperature, the SiO gas flowing into the second condenser is rapidly cooled, and a large amount of fine particles due to uniform nucleation are generated in the gas phase. . Since the SiO condensation rate due to the generation of fine particles is generally the same or higher than the rate at which SiO is condensed on the wall of the condenser, almost the entire amount of SiO gas can be condensed in the second condenser. The SiO fine particles generated in the gas phase are then deposited on the wall of the condenser on which the SiO solid has grown or are exhausted out of the system through a vacuum pump. At this time, if there is no SiO condensate on the wall surface of the vacuum pump, the SiO fine particles passing through the vacuum pump are not adsorbed on the wall surface of the vacuum pump and do not hinder the operation of the vacuum pump. However, when the SiO gas partial pressure in the second condenser is extremely low, the generation of SiO fine particles in the gas phase is significantly inhibited. For this reason, when the uncondensed SiO gas flows into the vacuum pump, SiO condensation occurs and grows on the wall surface of the vacuum pump, thereby hindering the operation of the vacuum pump. Therefore, the mass ratio of the SiO gas flowing into the second condenser to the SiO generation rate needs to be at least 0.1%.

  Next, from the viewpoint of the P concentration in the SiO solid recovered from the first condenser, the mass ratio of the SiO gas flowing into the second condenser with respect to the SiO generation rate is preferably at least 1%. The inventor found out. This is because when the SiO exhausted from the first condenser is less than 1%, the P concentration in the SiO solid recovered by the first condenser is clearly higher than that exhausted at this mass ratio or higher. Because it is inferior.

  Next, the upper limit of the mass ratio of the SiO gas flowing into the second condenser with respect to the SiO generation rate will be described. In principle, there is no such upper limit in the present invention. However, increasing the displacement from the first condenser to the second condenser reduces the yield of higher purity SiO solids recovered in the first condenser relative to the SiO generated from the raw material. It will be. Therefore, from the viewpoint of economy, the mass ratio of the SiO gas flowing into the second condenser with respect to the SiO generation rate is preferably, for example, 50% or less.

  The second condenser condenses SiO or the like that has passed through the first condenser, and the gas temperature inside the second condenser is usually lower than the gas temperature inside the first condenser. . By setting as such, SiO having higher purity can be efficiently recovered in the first condenser. Furthermore, it is desirable that the condensation surface temperature of the second condenser is 100 ° C. or less, preferably in the range of less than 100 ° C. to −50 ° C., more preferably in the range of less than 100 ° C. to room temperature. By setting the temperature to 100 ° C. or lower, most of the SiO gas that has passed through the first condenser and the condensable gas such as the impurity P can be condensed and excluded from the gas phase.

  Next, the SiO adhering to the first condenser is recovered. As a recovery method, a conventionally used method can be adopted. For example, the entire condenser is cooled, and solid SiO is peeled off and collected.

  The substance adhering to the second condenser is recovered from the condenser by, for example, scraping off the condensation surface as appropriate in an off-line operation or the like.

  Thus, since the condensable gas is condensed by the first and second condensers, the remaining small amount of non-condensable gas is sucked into the vacuum pump.

  By the above-described method, the phosphor contains 7 ppm or less of phosphorus, 0.3 ppm or less of boron, 0.1 ppm or less of arsenic, antimony, gallium, and indium, respectively, and a total of other metal impurities of 20 ppm or less. A raw material for producing high-purity silicon that is silicon oxide is obtained. In particular, the amount of P as an impurity can be greatly reduced.

As a method for purifying SiO, when the SiO is obtained from a mixed raw material of C and SiO ₂ , the present invention can be applied based on the same concept.

(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.

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, impurities of metal Si are 40 ppm for P, 9 ppm for B, 1500 ppm for Fe, and 500 ppm for other metal components, and impurities in high-purity silica sand are 0.3 ppm for P and B is 0. 5 ppm, Fe was 400 ppm, and other metals were 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. The generated SiO gas was solidified on the inner wall of the first condenser whose outside was air-cooled to form a solid SiO film. The gas temperature in the first condenser at this time was 300 to 1000 ° C. The second condenser was a 2m square, stainless steel box-type container, and the outside was water-cooled. The average gas temperature in the second condenser was 70 ° C. The SiO mass exhausted to the second condenser with respect to the generated SiO mass was 10%. The first and second condenser internal pressures at this time were 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 inner wall of the disassembled first condensing container and recovered. The amount of P in the reused SiO was 200 ppm.

  The metal Si remaining in the crucible was 0.06 kg, and the solid SiO exfoliated and recovered from the first 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 6 ppm by mass, B was 0.3 ppm, Fe was 0.07 ppm, and other metal components were 1 ppm in total.

  According to this method, the repair frequency of the vacuum pump could be greatly reduced. That is, the repair frequency of the vacuum pump was 1/10 as compared with the case without the second condenser.

2. Production of Si Next, Si was extracted from SiO in the Si extraction step. Details are as follows. 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 6.7 ppm, B was 0.23 ppm, Fe was 0.08 ppm, and other metal components were 0.01 ppm.

  Next, P was removed in a vacuum degassing step. The details are as follows. The Si lump obtained in the previous step was placed in a high-purity graphite crucible having a diameter of 0.8 m and charged into a vacuum heating furnace. While heating and melting this Si, the pressure in the vacuum heating furnace is kept constant at 0.1 Pa by a vacuum pump, and degassing is performed for 5 hours while keeping the melt at 1710 ° C. Obtained. At this time, the inside of the furnace was a weak oxidizing atmosphere. In the result of component analysis of Si, P was 0.05 ppm, B was 0.23 ppm, Fe was 0.07 ppm, and other metal components were 0.01 ppm, which satisfied the component reference value of Si for solar cell substrates.

It is a schematic drawing which shows an example of SiO refinement | purification apparatus.

Explanation of symbols

1 reaction vessel,
3 crucible,
5 mixed raw materials,
7 Heating device,
9 Vacuum pump,
11 first condenser,
15 second condenser,
17 Pressure gauge,
19 SiO gas,
21 SiO solid,
23 Impurity vapor,
25 Deposits.

Claims (6)

  In a SiO purification apparatus including a SiO generator, a first SiO condenser, and an exhaust pump, a second SiO condenser is disposed between the first SiO condenser and the exhaust pump. A purification device characterized by.   A method for purifying SiO, comprising using the purifier according to claim 1.   The method according to claim 2, wherein SiO gas is allowed to flow into the second SiO condenser at a rate of 0.1% or more of the SiO generation rate.   The method according to claim 2 or 3, wherein a gas temperature inside the second condenser is set lower than a gas temperature inside the first condenser.   The method according to any one of claims 2 to 4, wherein a condensation surface temperature of the second condenser is 100 ° C or less.   A method for producing high-purity Si, characterized in that the purified SiO according to any one of claims 2 to 5 is used.

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