JP2006315879A - Dephosphorization purification apparatus of silicon and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for dephosphorizing and purifying silicon realizing sufficient rate of removing impurities by promoting diffusion of impurity concentration in the silicon melt in the removal of impurities represented by phosphorus by virtue of the vacuum fusion method. <P>SOLUTION: This dephosphorization purification apparatus of silicon is equipped with a crucible 4 for accommodating silicon and a heating device for heating the crucible 4 both disposed in a vacuum container 2 provided with a vacuum pump 1, where an agitating device 6 is installed to agitate the silicon melt 3 in the crucible 4. The method for dephosphorizing and purifying silicon utilizes the apparatus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a refining apparatus and a refining method for refining from an inexpensive metal silicon raw material having a high impurity concentration to high-purity silicon used for manufacturing solar cells and the like.

  As silicon raw materials for manufacturing solar cells, scrap silicon generated in the semiconductor manufacturing process has been used so far. However, due to the rapid growth in demand for solar cells in recent years, the supply of scrap cannot catch up, and there is a concern that the supply of silicon raw materials for solar cells will be short in the future. The silicon raw material used in the semiconductor manufacturing process is manufactured using the Siemens method, but the silicon raw material manufactured by the Siemens method is expensive and does not match the cost of the route directly supplied to the solar cell manufacturing process. . Therefore, development of a metallurgical process for producing high-purity silicon from an inexpensive metal silicon raw material having a high impurity concentration by using vacuum melting or solidification purification has been advanced.

  The above metallurgical process is a process in which several metallurgical sub-processes utilizing a difference in physical behavior between an impurity element and silicon (Si) are combined for purification. For a sub-process for removing an impurity element having a higher vapor pressure than Si represented by phosphorus (P), application of a vacuum melting method has been studied. Hereinafter, expressions such as phosphorus removal (P removal) or dephosphorization (deP) by a vacuum melting method are used, but an impurity element having a higher vapor pressure than Si other than P is also removed along with P removal.

  As a basic configuration of an apparatus used for the vacuum melting method, a heating apparatus such as a crucible and a heater is installed in a vacuum container having a vacuum pump capable of reducing pressure. A crucible is filled with a metal silicon raw material containing high P of several tens of ppm or more, and heated and melted under reduced pressure or under an inert gas, and the molten metal is kept under reduced pressure and at a temperature equal to or higher than the melting point for a certain time. Since P having a higher vapor pressure than Si evaporates selectively, the P concentration in Si decreases with time.

  Up to now, there are conventional techniques for refining silicon by a vacuum melting method such as (Patent Document 1), (Non-Patent Document 1), (Non-Patent Document 2), (Non-Patent Document 3), and (Non-Patent Document 4). In these prior arts, it is a combination of a crucible installed in a depressurizable container and a general heating device, and the device cost is low. However, the P removal rate is low, that is, the productivity is low and there is a problem in practical use. In addition, in the above-mentioned document, it has been reported that the P concentration in silicon cannot be reduced to about 0.05 ppm or less, which is required as a raw material for solar cells, and there is a problem in quality.

On the other hand, (Non Patent Literature 5), (Patent Literature 2), (Patent Literature 3), (Patent Literature 4), (Patent Literature 5), (Patent Literature 6), (Patent Literature 7), (Patent Literature 8). In the conventional technology such as P, the P removal rate is high, and the production cost is practical. However, these prior arts are based on the premise of electron beam melting, and the equipment and equipment cost become enormous, and there is a practical problem in terms of equipment cost. In particular, as disclosed in (Patent Document 2) and (Patent Document 7), in the method using an electron beam, it is necessary to set a plurality of crucibles in a vacuum vessel, and there is a problem that a larger equipment cost is required. there were.
U.S. Pat. No. 4,304,763 Japanese Patent Application Laid-Open No. 7-315827 JP-A-7-309614 JP-A-9-309716 Japanese Patent Laid-Open No. 10-167716 JP-A-10-182130 Japanese Patent Laid-Open No. 11-209195 JP 2000-247623 A Suzuki et al., Journal of the Japan Institute of Metals, February 1990, Vol. 54, No. 2, p. 161-167 Ikeda et al., IISJ International, 1992, Vol. 32, no. 5, p. 635-642 Yushita et al., Journal of the Japan Institute of Metals, October 1997, Vol. 61, No. 10, p. 1086-1093 Morita, Metals, Agne Technical Center, 1999, Vol. 69, No. 11, p. 949 Photovoltaic Material Technology Association, 1998 Energy and Industrial Technology Development Organization, Survey and Research on Practical Use Analysis of Solar Cell Silicon Raw Material Manufacturing Technology, March 1999, p. 81

  Therefore, the present inventors have proposed, as Japanese Patent Application No. 2004-44255, a silicon purification apparatus and method using an impurity condensing apparatus as a simpler technique than before. The invention of Japanese Patent Application No. 2004-44255 is a silicon refining device in which a crucible containing silicon and a heating device for heating the crucible are installed in a decompression vessel equipped with a vacuum pump, and the inside of the crucible A silicon refining device is used, which is characterized in that an impurity condensing device is arranged at a position where one or both of the surface of the molten silicon or the crucible opening can be seen, and a simple and inexpensive device configuration is sufficient. The present invention provides a low-cost silicon purification apparatus and a purification method that achieve a high P removal rate.

  However, in the course of carrying out the invention, the following new problem that hinders the P removal treatment by the vacuum melting method has been clarified.

  It became clear that the shape of the molten silicon held in the crucible has a great influence on the P removal rate. (Depth of molten metal) / (Diameter of molten metal surface) is defined as the aspect ratio of the molten metal. In a conventional test, treatment was performed with a small crucible with a small aspect ratio, in which case the P removal rate was proportional to the molten metal surface area. By increasing the surface area of the molten metal, that is, by using a crucible having a large diameter, it was possible to increase productivity. However, in an actual processing apparatus, since it is necessary to further increase the silicon processing amount and increase the productivity, it is necessary to select a deep crucible shape having a somewhat large aspect ratio. Therefore, as a result of conducting a test using a crucible having a large aspect ratio, it was found that the diffusion of P in the molten silicon becomes rate-limiting as the aspect ratio increases. That is, if the processing time increases in proportion to the depth of the molten silicon, the productivity for processing per unit mass is not changed, but the processing time is further increased, and the productivity is greatly deteriorated. .

  Accordingly, an object of the present invention is to provide a silicon de-P purification apparatus that promotes diffusion of P in a molten silicon and has a sufficient P removal rate, and a silicon de-P purification method using the same.

The present invention has been made to solve the above problems,
(1) A silicon de-P refining device comprising at least a crucible for storing silicon and a heating device for heating the crucible in a vacuum container equipped with a vacuum pump, which is housed in the crucible. A silicon de-P purifying apparatus characterized by comprising a stirring apparatus for molten silicon,
(2) The silicon de-P purification apparatus according to (1), wherein the stirring device includes a stirring blade installed in the silicon melt and a rotating device that rotates the stirring blade.
(3) The silicon de-P refining device according to (1), wherein the stirring device comprises an inert gas jet pipe in which a jet port is disposed in the molten silicon.
(4) The silicon de-P purification apparatus according to (1), wherein the stirring device is an induction stirring device using an electromagnet disposed outside the heating device,
(5) The silicon de-P purifying apparatus according to (1), wherein an impurity condensing device is disposed at a position where one or both of the surface of the molten silicon or the crucible opening in the crucible can be seen (a position that can be expected).
(6) The silicon de-P purification device according to (5), wherein the impurity condensing device has a cooling device,
(7) The silicon de-P purification apparatus according to (5) or (6), including a first lifting device that allows the impurity condensing device to be lifted and lowered.
(8) The silicon de-P purification apparatus according to (7), wherein a preparation chamber for storing an impurity condensing device is disposed in the decompression vessel,
(9) The silicon de-P purification apparatus according to (5), further including a second lifting device that allows the crucible to be lifted and lowered.
(10) A silicon purification method using the silicon de-P purification apparatus according to any one of (1) to (9), wherein the inside of the decompression vessel is set to 500 Pa or less, and the silicon in the crucible is set to a melting point or more. A silicon de-P purification method characterized by removing impurities mainly composed of P evaporating from the silicon melt while heating and stirring the silicon melt with a stirrer,
It is.

  According to the present invention, diffusion of P in the molten silicon can be promoted, a large P removal rate can be obtained, and an inexpensive and high-purity silicon raw material for solar cells can be supplied.

  The present invention is a silicon dephosphorization purification apparatus and purification method using a simple apparatus comprising a crucible set in a vacuum container and a general heating apparatus. However, although the expression dephosphorization (dephosphorization) is used as an apparatus and method for the purpose of removing phosphorus (P), other than P, for example, aluminum (Al), arsenic (As), antimony ( Sb), lithium (Li), magnesium (Mg), zinc (Zn), sodium (Na), calcium (Ca), nickel (Ni), germanium (Ge), copper (Cu), tin (Sn), silver ( The present invention is also applicable to the removal of elements having a higher vapor pressure than silicon (Si) such as Ag), indium (In), manganese (Mn), lead (Pb), and thallium (Tl).

  With respect to the first invention, the configuration of the purification apparatus will be described with reference to FIG. First, a crucible 4 for holding a silicon melt 3 and a heating device 5 for dissolving silicon and holding it in a liquid phase are set in a depressurizable container 2 equipped with a vacuum pump 1. At the upper part of the crucible 4, a molten metal stirring device 6 is arranged.

  The vacuum pump 1 only needs to be able to depressurize to 500 Pa or less, and an oil rotary pump alone is sufficient. However, a mechanical booster pump may be provided according to the size of the container 2, and an oil diffusion pump or a turbo molecular pump may be provided. It is also possible to shorten the vacuum sweep time and further shorten the P removal time.

  The crucible 4 is optimally made of high-density graphite that does not generate a reaction gas with silicon. Quartz crucibles react with silicon under high vacuum to generate silicon oxide (SiO) gas, so there is a problem that high vacuum cannot be maintained, or there is a problem that the molten silicon bumps into boil, and silicon purification It is not suitable for vacuum melting.

  Any heating device 5 can be applied as long as it can be heated to the melting point of silicon or more. However, a heater heating method in which a voltage is applied to a heating element such as graphite and the crucible 4 and the molten silicon 3 are heated by Joule heating is the most. Convenient. An induction heating method in which an induction coil is disposed outside the graphite crucible 4 and the silicon melt 3 is heated by heating the graphite crucible by an induced current is also a low-cost heating method. Both heating apparatuses are simple heating methods for melting metals that are widely used in general.

  The molten metal stirring device 6 which is the point of the present invention will be described in detail. The molten metal stirring device 6 in FIG. 1 includes a stirring blade 7, a rotating shaft 8, a vacuum seal 9, a rotating motor (rotating device) 10, and a lifting device 11. The stirring blade 7 is inserted into the molten metal, and the stirring blade 7 is rotated through the rotating shaft 8 by the rotation motor 10 to stir the molten metal. The size of the stirring blade 7 is preferably not less than 0.3 times the diameter of the crucible 4 in order to sufficiently stir the entire molten metal, and 0.95 times to ensure mechanical clearance with the crucible inside. The following diameters are preferred. That is, a range of 0.3 to 0.95 times is preferable. Further, the rotational speed is preferably 10 rpm or more, but if it is too large, there is a problem that the molten silicon is scattered, and the range up to 120 rpm is preferable. That is, a range of 10 to 120 rpm is preferable. The material of the stirring blade and the rotating shaft is preferably ceramics such as quartz, alumina and magnesia, or graphite, which is excellent in heat resistance and less deteriorated by reaction with silicon, but graphite is the most excellent. However, if these materials are used in a portion in contact with the vacuum seal 9, the processing accuracy and wear resistance are inferior, which may cause leakage. For this reason, it is desirable that the rotary shaft 8 is divided and the upper part is made of a metal material such as stainless steel. By providing the lifting device 11, the insertion position of the stirring blade 7 can be adjusted according to the state of the raw material inserted into the crucible and the position of the crucible. Moreover, it is possible to obtain a larger stirring effect by rotating the stirring blade and periodically moving it up and down at the same time. It is preferable that the vertical movement period is once per 5 to 30 revolutions and the stroke is as large as possible in the range from the bottom of the crucible to the melt surface. It is desirable that the vacuum seal 9 has a specification (for example, a magnetic seal) that can hold the container 2 in a vacuum state even when the rotation shaft repeatedly rotates and moves up and down.

  FIG. 2 shows a case where the molten metal stirring device 6 is constituted by a gas introduction mechanism. The molten metal stirring device 6 includes a gas introduction pipe (inert gas ejection pipe) 12, a vacuum seal 9, and a lifting device 11. The gas introduction pipe 12 is inserted into the molten metal, and the gas is fed into the molten metal to stir the molten metal. The material of the gas introduction pipe 12 is preferably ceramics such as quartz, alumina, and magnesia, or graphite, which is excellent in heat resistance and less deteriorated by reaction with silicon, but graphite is most excellent. However, if these materials are used in a portion in contact with the vacuum seal 9, the processing accuracy and wear resistance are inferior, which may cause leakage. Therefore, it is desirable that the gas introduction pipe 12 is of a split type and the upper part is made of a metal material such as stainless steel. The effect of the invention is manifested even if only one gas ejection hole (ejection outlet) is provided at the tip of the pipe, but the stirring effect is increased by installing a plurality of holes within a range that can be installed in the melt. The hole diameter is preferably as small as possible in order to increase the ejection speed, but if it is too small, clogging occurs, so a diameter of 0.5 mm or more and 3 mm or less is preferable. Moreover, the effect of agitation is increased by branching a plurality of pipes horizontally from the tip and installing gas ejection holes not only in the melt center but also in the surrounding area. The stirring effect is further increased by providing a plurality of ejection holes in the plurality of branching vipes. In this case, the stirring effect is further increased by rotating the pipe. Rotating the pipe is effective in increasing the stirring effect by introducing a plurality of pipes.

  By providing the lifting / lowering device 11, the insertion position of the gas introduction pipe 12 can be adjusted according to the state of the raw material inserted into the crucible and the position of the crucible. The vacuum seal 9 desirably has a specification (for example, a magnetic seal) that can hold the container 2 in a vacuum state even when the gas introduction pipe 12 repeatedly moves up and down. The amount of gas introduced depends on the diameter and number of holes. However, if the amount of gas introduced is too large, the degree of vacuum in the container decreases and the P removal rate decreases. Since it also depends on the exhaust capacity of the vacuum vessel or vacuum pump, the amount of gas introduced is preferably an amount that can maintain a pressure of 500 Pa or less, more preferably an amount of gas that is less than an amount capable of maintaining a pressure of 10 Pa or less. preferable.

FIG. 3 shows a case where the molten metal stirring device 6 is constituted by an electromagnetic induction stirring device using an electromagnet disposed outside the heating device 5. The electromagnetic induction stirrer is disposed outside the vacuum vessel 2 that is less affected by heat because the distance over which the stirring force reaches is relatively long. Exciting a flow different from normal thermal convection greatly increases the diffusion rate of P in Si. The number of slots of the electromagnetic coil 13 (number of magnetic poles, generally about 12) and the number of poles (2 × n when the period of the electromagnetic field is n cycles per round, generally 2 to 4) are general. The specifications are fine. The frequency is preferably about 0.1 to 10 Hz. The smaller the frequency, the greater the distance at which the electromagnetic field is induced. Therefore, it is preferable that the frequency be small as the apparatus becomes larger. The stirring force applied to silicon is about 10 N / m ³ .

  The fifth invention is a de-P purifying apparatus in which an impurity condensing device is added to the silicon de-P purifying apparatus described in the first invention. This will be described in detail with reference to FIG. The code | symbol 14 described in FIG. 4 is the impurity condensing part of an impurity condensing apparatus. The impurity condensing part 14 is disposed at a position where the molten metal surface and the crucible opening in the upper part of the crucible 4 can be seen (a position to be seen), and P evaporated from the molten metal surface together with Si and SiO is the impurity condensing part 14. The Si—SiO film in which P is concentrated at a high concentration adheres to the surface of the impurity condensing part 14. The impurity condensing part 14 in FIG. 4 is a cylinder formed by combining metals such as iron, stainless steel, and copper, graphite, alumina, or a plurality of these materials.

  6th invention adds the cooling device which introduce | transduces and cools the refrigerant | coolants 15, such as water, to the impurity condensation part 14. FIG. The surface of the impurity condensing part 14 is cooled by flowing the refrigerant 15 in the direction of the arrow in the figure. By cooling the surface, the P removal effect is further increased.

  7th invention is the silicon | silicone refinement | purification apparatus which added the raising / lowering apparatus (1st raising / lowering apparatus) 20 to the impurity condensing apparatus like FIG. With this configuration, it is possible to keep the distance between the impurity condensing part 14 and the molten metal surface, or the distance between the impurity condensing part 14 and the crucible opening.

  The eighth invention will be described with reference to FIGS. 4 (a) and 4 (b). The present invention is an apparatus configuration indispensable in continuous operation. Although the Si-SiO film in which P is concentrated at a high concentration adheres to the impurity condensing part 14, it peels off when the film thickness exceeds a certain level, falls into the treated silicon, and the P concentration rises again. Need to be cleaned. In the apparatus of FIG. 4, the depressurizable container includes a processing chamber 16 and a preliminary exhaust chamber 17 (preparation chamber). The processing chamber 16 and the preliminary exhaust chamber 17 can be partitioned by a gate valve 18. The processing chamber 16 and the preliminary exhaust chamber 17 are each equipped with a vacuum pump 1, 1 ′, and the preliminary exhaust chamber 17 can be freely reduced from atmospheric pressure to reduced pressure to atmospheric pressure without breaking the vacuum of the processing chamber 16. I can go back and forth. The impurity condensing unit 14 includes an elevating device 20 that freely moves between the processing chamber 16 and the preliminary exhaust chamber 17 across the position of the gate valve 18. Since the gate valve 18 is opened and closed, the molten metal stirring blade 7 is also configured to be movable between the processing chamber 16 and the preliminary exhaust chamber 17 by the lifting mechanism 11. In addition, the preliminary exhaust chamber 17 is equipped with a door 19 for cleaning the impurity condensing unit 14 and replacing parts of the molten metal stirring device 6. 4A shows the state of the apparatus during impurity removal, and the molten metal stirring blade 7 and the impurity condensing unit 14 are in the processing chamber 16. FIG. FIG. 4B shows a state of the apparatus when the impurity condensing unit 14 is cleaned, and the melt stirring blade 7 and the impurity condensing unit 14 are in the preliminary exhaust chamber 17.

  The ninth invention is a silicon refining device in which an elevating device (second elevating device) is added to the crucible 4. As in the seventh invention, the distance between the impurity condensing part 14 and the molten metal surface, or the distance between the impurity condensing part 14 and the crucible opening can be kept optimal.

  A tenth aspect of the present invention is a silicon purification method in which the inside of the container is depressurized to 500 Pa or less and the silicon is heated to the melting point or higher and dissolved and held using the apparatus of the first to ninth aspects. By this method, it is possible to eliminate the diffusion rate limiting in the molten Si of P, or both the diffusion rate limiting rate in the molten Si and the vapor phase diffusion rate limiting of P, and to remove the impurity element from the silicon at a high removal rate. Under a pressure higher than 500 Pa, the impurity removal rate is low, which causes a practical problem. Further, a high impurity removal rate can be obtained by reducing the pressure preferably to 10 Pa or less.

  Now, the principle by which the present invention improves the impurity removal rate will be described by taking P removal as an example. Here, P is described as a representative element having a higher vapor pressure than Si, and the basic principle described below is based on all elements having a higher vapor pressure than Si, for example, Al, As, Sb, Li, Mg, Zn. , Na, Ca, Ni, Ge, Cu, Sn, Ag, In, Mn, Pb, and Tl can be applied to remove elements having a higher vapor pressure than Si.

  The process of removing P from the Si liquid phase includes (a) diffusion of P in the Si liquid phase, (b) evaporation of P from the Si liquid phase surface to the gas phase, and (c) P in the gas phase. It consists of three elementary processes: diffusion. That is, P diffuses in the Si liquid phase, reaches the gas-liquid interface, and evaporates at the gas-liquid interface. Any one of the elementary processes (a) to (c) that controls the movement of P most determines the total P removal speed.

  First, the principle that the molten metal stirring device of the present invention improves the P removal rate will be described. When the depth of the molten silicon is shallow, the diffusion of P in the liquid phase is sufficiently fast, and there is almost no difference in the concentration of P in the depth direction of the molten silicon. Therefore, the diffusion in the liquid phase of (a) is rate limiting. It is not a process. However, when the depth of the molten silicon increases, even if the moving speed of P in the liquid phase does not change (when it is shallow), there is a difference in the concentration of P in the depth direction of the molten silicon, and the reaction (b) The driving force of the process is reduced, and therefore the P removal rate is reduced. Specifically, when the depth of the molten silicon is up to about 100 mm, the P removal processing time increases in proportion to the depth of the molten silicon, and the P removal rate does not depend on the depth of the molten silicon. However, when the depth of the molten silicon exceeds 100 mm, it becomes necessary to perform the P removal treatment for a time that is clearly longer than the P removal treatment time proportional to the depth of the molten silicon. Further, in the range where the depth of the molten silicon exceeds about 500 mm, the P removal processing time is proportional to the square of the depth of the molten silicon, and the P removal rate is approximately inversely proportional to the depth of the molten silicon. is there. If the molten metal stirring apparatus of the present invention is used, the moving speed of P in the liquid phase itself increases, so that even if the depth of the molten silicon increases, the concentration difference of P in the depth direction of the molten silicon decreases. The degree of rate limiting of diffusion in the liquid phase of a) can be weakened.

  Next, the principle that the impurity condensing apparatus of the present invention improves the P removal rate will be described. The P molecules detached from the surface of the molten metal are exhausted to the vacuum pump, or reach and adhere to any surface in the decompression vessel. However, as can be seen from the high vapor pressure of P, the adhesion coefficient is low and the probability of re-evaporation is high. In particular, the inside of the decompression vessel is at a high temperature due to radiation and heat transfer, and the probability of reevaporation is even higher. Therefore, P is not quickly exhausted out of the system, and the P concentration in the gas phase cannot be quickly reduced. In the prior art that does not use the electron beam melting method, the P concentration in the gas phase is decreased at a low rate and the driving force for P evaporation is small by simply evacuating the P released in the gas phase to a vacuum pump. Therefore, the P removal rate is small. That is, in the prior art, the diffusion of P in the gas phase in (c) has been a rate-determining process.

Now, although the vapor pressure of Si is lower than that of P, since P in Si originally has a concentration of several tens of ppm, Si has a larger evaporation amount. Therefore, one or both of Si and SiO always fly on the surface of the impurity condensing apparatus of the present invention. Since the surface temperature is lower than the melting point of Si and SiO, one or both of Si and SiO are solidified and evaporated. However, SiO is generated by reacting Si vapor with one or both of O ₂ (oxygen) remaining in one or both of the Si liquid phase and the gas phase, or O ₂ due to leakage. If only P comes to the surface of the impurity condensing device, P has a high probability of re-evaporation. However, if one or both of Si and SiO is solidified on the surface where P has just arrived, since P has a high affinity with Si and SiO, P is solid-solidified in those solids, ie traps. Is done. That is, it is quickly removed from the gas phase. That is, the impurity condensing apparatus of the present invention dramatically increases the diffusion rate of P in the gas phase, and weakens the rate limiting rate in the gas phase diffusion process.

(Example 1)
An overview of the equipment used is shown. The basic structure conforms to FIG. The vacuum vessel has a water-cooled jacket structure and is equipped with a two-stage vacuum pump of an oil rotary pump and a mechanical booster pump. Inside the vacuum vessel is a high-purity graphite crucible with an outer diameter of 1000 mm, an inner diameter of 900 mm, and a depth (inner dimension) of 700 mm, a high-purity graphite heater at a position covering the side and bottom of the crucible, and a carbon insulation on the outside. is set up. A graphite heater can supply a maximum of 300 kW of power.

  The molten silicon stirring device is basically a 600 mmφ two-blade shaped stirring blade made of high-density graphite, and is attached to a high-density graphite rotating shaft having a length of 1500 mm and a diameter of 50 mm. Further, the rotating shaft is made of a stainless steel rotating shaft. It is linked to. A vacuum seal mechanism is attached to the introduction hole of the vacuum vessel, and the atmosphere is sealed by the stainless steel rotating shaft. The stainless steel shaft is further connected to a rotary motor and a lifting mechanism, and the vacuum seal mechanism is designed to keep the inside of the container in a vacuum even when the stainless steel shaft is rotated and lifted. The number of rotations was 60 rpm at the maximum, and the lifting stroke was 1000 mm.

  In the P removal process, the silicon raw material is filled in the crucible in the cold, and then vacuum sweep is performed. After reaching a vacuum level of 5.0 Pa or less, the heater was energized to start melting. After all the silicon raw materials were completely dissolved, they were heated and held in a vacuum. As the silicon raw material to be filled, one having an initial P concentration of 30 ppm was used. The P concentration of silicon after the treatment was measured using ICP emission analysis, and the P removal rate was evaluated in consideration of time and the amount of silicon.

  In all of the examples and comparative examples, 150, 300, 600, and 900 kg of silicon raw material were treated, and the dependency of the P removal rate on the depth of the molten silicon was tested. The treatment time was proportional to the mass of the molten metal, and 150, 300, 600, and 900 kg of silicon raw material were treated for 2, 4, 8, and 12 hours, respectively, after confirming the completion of melting. In the examples, the stirring blade was retracted above the crucible before melting, and after melting, the stirring blade was inserted into the molten metal and rotated at 30 rpm. In the comparative example, stirring with a stirring blade was not performed.

  Table 1 lists the comparative examples, and Table 2 lists the results of this example. In the case where stirring was not performed, the P removal rate decreased almost in inverse proportion to the amount of silicon. When stirring was performed, the P removal rate slightly decreased as the amount of silicon was increased, but the processing rate was 1.15 to 4.5 times larger than that of the comparative example with the same amount of silicon. Is very expensive.

(Example 2)
In this example, the same apparatus as that described in Example 1 was used, and silicon was processed under the same conditions. The difference is that the graphite agitation blade and rotating shaft, stainless steel rotating shaft, and motor used in Example 1 were removed, and a graphite pipe having an outer diameter of 30 mm, an inner diameter of 20 mm, and a length of 1500 mm was connected to the stainless steel pipe. Replaced with piping. A graphite pipe can be inserted into the silicon melt, and the stainless steel pipe passes through the vacuum seal portion of the vacuum vessel. The stainless steel pipe was connected to an Ar gas cylinder so that Ar gas could be introduced into the molten silicon. As in Example 1, the pipe was withdrawn above the crucible before melting, the pipe was inserted into the molten metal after melting, and Ar was introduced into the molten metal. The amount of Ar introduced was 1.0 mL / min, and the degree of vacuum was 10 Pa.

  Table 3 lists the results of this example. In this example, as in Example 1, the P removal rate was slightly reduced as the amount of silicon was increased. However, the processing rate was 1.02 to 4.0 times larger than that of the comparative example with the same amount of silicon, and the stirring rate was increased. The effect of was remarkable.

(Example 3)
Also in this example, the same apparatus as that described in Example 1 was used, and silicon was processed under the same conditions. The difference was that the graphite stirring blade and rotating shaft, stainless steel rotating shaft and motor used in Example 1 were removed, and an electromagnetic coil for induction stirring was attached to the outside of the vacuum vessel. The approximate shape of the entire electromagnetic coil is a donut shape having an outer diameter of 3300 mm, an inner diameter of 2500 mm, and a height of 1000 mm. The slot was 12, the iron core of the magnetic pole had a length of 300 mm, a rectangular cross section of 200 mm × 500 mm, and the coil of each magnetic pole had 300 turns. The frequency was designed at 2 Hz and the number of poles was 4.

  Table 4 lists the results of this example. In this example, as in Example 1, the P removal rate slightly decreased as the amount of silicon was increased. However, the processing rate was 1.06 to 4.2 times larger than that of the comparative example with the same amount of silicon, and the stirring rate was increased. The effect of was remarkable.

(Example 4)
In this example, 900 kg of silicon was purified by an apparatus similar to the specification of FIG. 4 (Table 5). When the impurity condensing apparatus was not used, the impurity condensing apparatus was used but the cleaning was not performed. When the impurity condensing apparatus was used, the impurity condensing part was cleaned every two hours, and the comparison was made in three cases. When the impurity condensing apparatus was not used, the P removal rate was almost the same as in Example 1. When the impurity condensing device was used, the P removal rate was about 3 times as high as when the impurity condensing device was not used. When the impurity condensing device was cleaned, the P removal rate was about 5 times higher than when the impurity condensing device was not used.

It is a conceptual diagram (stirring blade stirring) of the silicon purification apparatus of the present invention. It is a conceptual diagram (gas stirring) of the silicon refinement | purification apparatus of this invention. It is a conceptual diagram (electromagnetic stirring) of the silicon refinement | purification apparatus of this invention. It is a conceptual diagram of the apparatus which added the impurity condensing apparatus, Comprising: It is an apparatus state at the time of P removal process. It is a conceptual diagram of the apparatus which added the impurity condensing apparatus, Comprising: It is an apparatus state when cleaning an impurity condensing apparatus.

Explanation of symbols

1 vacuum pump,
2 Depressurizable container,
3 Silicon melt,
4 Crucible,
5 heating device,
6 Molten metal stirring device,
7 stirring blades,
8 rotation axis,
9 Vacuum seal,
10 motor,
11 Lifting device,
12 Gas introduction pipe,
13 Electromagnetic coil,
14 Impurity condensation section,
15 refrigerant,
16 treatment room,
17 Spare room,
18 Gate valve,
19 Door,
20 Lifting device for impurity condensing part.

Claims (10)

A dephosphorizing and purifying apparatus for silicon comprising at least a crucible containing silicon and a heating device for heating the crucible in a vacuum container equipped with a vacuum pump,
An apparatus for dephosphorizing and purifying silicon, comprising a stirring device for molten silicon contained in the crucible.   The silicon dephosphorization and purification apparatus according to claim 1, wherein the stirring device comprises a stirring blade installed in the molten silicon and a rotating device for rotating the stirring blade.   The silicon dephosphorizing and purifying apparatus according to claim 1, wherein the stirring device comprises an inert gas jet pipe having a jet port disposed in the molten silicon.   The silicon dephosphorizing and purifying apparatus according to claim 1, wherein the stirring apparatus comprises an induction stirring apparatus using an electromagnet disposed outside the heating apparatus.   2. The apparatus for dephosphorizing and purifying silicon according to claim 1, wherein an impurity condensing device is disposed at a position where one or both of the surface of the molten silicon or the crucible opening in the crucible can be seen.   The silicon dephosphorization purification apparatus according to claim 5, wherein the impurity condensing apparatus includes a cooling device.   The silicon dephosphorization purification apparatus according to claim 5, further comprising a first lifting device that allows the impurity condensing device to freely move up and down.   The silicon dephosphorization purification apparatus according to claim 7, wherein a preparation chamber for storing an impurity condensing apparatus is disposed in the decompression vessel.   The silicon dephosphorization purification apparatus according to claim 5, further comprising a second elevating device that allows the crucible to be moved up and down. A silicon purification method using the silicon dephosphorization purification apparatus according to any one of claims 1 to 9,
The inside of the decompression vessel is set to 500 Pa or less, and while the silicon in the crucible is heated to a melting point or higher, and the molten silicon is further stirred with a stirrer, impurities mainly composed of phosphorus evaporating from the molten silicon are removed. To dephosphorylate and purify silicon.