JP2007191342A - Apparatus and method for purifying silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for purifying silicon which is composed of a comparatively simple and inexpensive apparatus, has remarkably high removal speed for P, and can separate and remove impurities such as P in a raw material silicon industrially, easily and inexpensively, and by which high-purity silicon useful for a solar cell or the like can be manufactured commercially. <P>SOLUTION: The apparatus is equipped with a chamber having pressure reduced to a prescribed value or less by a pressure-reducing means, a crucible for housing silicon installed in the chamber under reduced pressure, and a heating means for heating silicon in the crucible, where silicon is heated and melted under reduced pressure and impurities in the molten silicon are separated and removed by evaporation. The apparatus is equipped with a ripple induction means for enlarging the liquid surface area of the molten silicon. This apparatus is used for the method for purifying silicon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a silicon purification apparatus for producing relatively high-purity silicon suitable for applications such as solar cells from inexpensive silicon having a relatively high impurity concentration, and a silicon purification method using the same.

  Silicon (Si) used in solar cells generally has a purity of 99.9999% by mass (6N) or more and various metal impurities are 0.1 ppm by mass or less, and phosphorus (P) has a purity of 0.8. It is said that it is necessary to be not more than 05 mass ppm. And as a silicon | silicone which satisfy | fills such conditions, the ultra high purity silicon of the purity 99.99999999999% (11N) or more used for a semiconductor use is known.

  However, the silicon used in this semiconductor application converts metallurgical grade metal silicon having a purity of about 98% by mass obtained by reducing silica into silicon chloride, and then pyrolyzes after distilling the silicon chloride. Manufactured by the so-called Siemens method, it requires a very complicated manufacturing process and extremely strict process control, which inevitably increases the manufacturing cost. For this reason, this silicon for semiconductor use is not suitable for a solar cell application for which cost reduction is required as demand increases, because it is excessive quality and manufacturing cost is too high.

  Therefore, conventionally, an inexpensive metallurgical grade metal silicon is used as a raw material, and this is further used in a metallurgical method, for example, by bringing molten silicon into contact with a lower density molten slag to remove impurities in the molten silicon. Slag refining method that moves to the inside and elements with higher vapor pressure than silicon, such as lithium (Li), sodium (Na), aluminum (Al), phosphorus (P), calcium (Ca), magnesium (Mg) ), Manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), germanium (Ge), arsenic (As), silver (Ag), indium (In), tin (Sn), antimony (Sb) ), Lead (Pb), thallium (Tl), etc. (hereinafter referred to as “impurities such as P”) are heated under reduced pressure and evaporated to separate and remove by evaporation, etc. Cheaper than purity 6N Attempts have been made to be manufactured at low cost silicon suitable for solar cell applications.

  Here, several proposals have been made regarding the vacuum melting method so far. For example, in Patent Document 1, Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4, and the like, decompression is possible. Proposed a silicon refining device having a relatively low-cost apparatus configuration comprising a simple decompression chamber, a crucible disposed in the decompression chamber, and a general heating device for heating silicon contained in the crucible It is described that impurities such as P are removed (the former method).

  In Non-Patent Document 5, Patent Documents 2-8, and the like, impurities such as P can be efficiently removed by using an electron beam as a heating means in a silicon purification apparatus equipped with a decompression chamber, a crucible, and a heating means. Removal is described (the latter method).

  However, the former method has a problem that the removal rate of phosphorus (P removal rate) is particularly slow and is not practical for industrial use, and the P concentration in silicon is a level required for solar cell applications. In some cases, it cannot be reduced to a certain level, and there is a problem in quality. In the latter method, the P removal rate is fast and industrially practical. However, since it is premised on electron beam melting, the equipment and equipment costs become enormous, and the production cost is low. Therefore, in practice, there is a problem that it is not practical in industry, and there is also a problem that it is necessary to accommodate a plurality of crucibles in the decompression chamber, which further increases the equipment cost.

Therefore, the present inventors previously determined that the P removal rate in the dephosphorization of silicon includes the diffusion rate of P in the molten silicon, the evaporation rate of P from the surface of the molten silicon, and the gas phase on the molten silicon. From this point of view, as a method for solving the above-mentioned various problems, in addition to the decompression chamber, the crucible, and the heating means, it is evaporated from the liquid surface of the molten silicon. A silicon purifier has been developed and proposed which has an impurity trapping means for efficiently trapping impurities such as P and improves the diffusion rate of P in the gas phase on the molten silicon (Japanese Patent Laid-Open No. 2005-231956).
U.S. Pat. Japanese Unexamined Patent Publication No. 7-315827 Japanese Unexamined Patent Publication No. 7-309614 JP-A-9-309716 JP-A-10-167716 Japanese Patent Laid-Open No. 10-182130 JP-A-11-209195 JP 2000-247623 A Suzuki et al., The Japan Institute of Metals, 54 (2), p.161 (1990) Ikeda et al., IISJ International, Vol.32, No.5, p.635 (1992) Yushita et al., The Japan Institute of Metals, 61 (10), p.1086 (1997) Morita, Metal, Vol.69, No.11, p.949 (1999) Photovoltaic Material Technology Association, 1998 New Energy and Industrial Technology Development Organization, Survey and Research on Practical Use Analysis of Solar Cell Silicon Raw Material Production Technology, p.81 (March 1999)

  The present invention includes a decompression chamber that is decompressed to a predetermined pressure or less by the decompression means, a crucible that is disposed in the decompression chamber and that contains silicon, and a heating means that heats the silicon in the crucible. In a silicon purification apparatus that heats and melts silicon and evaporates and removes impurities in the generated molten silicon, the amount of P evaporation from the molten silicon surface is further improved, thereby increasing the P removal rate. The processing time required to further increase the concentration of impurities such as P, particularly the P concentration to a predetermined value, for example, 0.05 mass ppm or less, preferably 0.02 mass ppm or less, is greatly shortened. As a result of intensive investigations on the possible methods, this can be achieved without increasing the opening area of the crucible opening by forming a predetermined ripple on the surface of the molten silicon in the crucible. The liquid surface area of the molten melt can be easily increased, and this can greatly promote the evaporation of impurities such as P from the molten metal surface without increasing the heat dissipation from the crucible opening. The present invention has been completed.

  Accordingly, an object of the present invention is a relatively simple and inexpensive apparatus configuration, and the P removal rate is remarkably fast, and impurities such as P in the raw material silicon can be separated and removed industrially easily and inexpensively. Thus, an object of the present invention is to provide a silicon purification apparatus capable of industrially advantageously producing high-purity silicon suitable for applications such as solar cells.

  Another object of the present invention is to use a relatively simple and inexpensive silicon refining apparatus to separate and remove impurities such as P in raw silicon easily and inexpensively because the P removal rate is remarkably fast. An object of the present invention is to provide a method for purifying silicon.

  That is, the present invention includes a decompression chamber that is decompressed to a predetermined pressure or less by the decompression means, a crucible disposed in the decompression chamber and containing silicon, and a heating means for heating the silicon in the crucible, A silicon purifier that heats and melts silicon under reduced pressure to evaporate and remove impurities in the generated molten silicon, and includes ripple-inducing means for increasing the surface area of the molten silicon. This is a silicon purification device.

  In addition, the present invention is the silicon purification apparatus provided with the silicon melt stirring means in addition to the ripple inducing means for increasing the liquid surface area of the silicon melt in the silicon purification apparatus. Furthermore, in the present invention, in the above-described silicon purification apparatus, in addition to the ripple inducing means for increasing the liquid surface area of the molten silicon, an impurity capturing means for capturing impurities evaporating from the liquid surface of the molten silicon is provided. This is a silicon purification device.

  Then, the present invention is a silicon purification method for removing phosphorus-based impurities in silicon using any of the above-described silicon purification apparatuses, wherein the pressure in the vacuum chamber is reduced to 500 Pa or less and the silicon in the crucible is reduced. It is a silicon purification method characterized in that it is heated to the melting point or higher and melted, and at the same time, a ripple-inducing means removes impurities mainly composed of phosphorus while forming ripples on the surface of the molten silicon in the crucible.

  In the present invention, the decompression chamber that is decompressed to a predetermined pressure or less by the decompression means is only required to be decompressed to 500 Pa or less and about 0.01 Pa by an appropriate decompression means, and the degree of vacuum of less than 0.01 Pa increases the cost. . A vacuum pump typically used for this purpose is a vacuum pump. For example, only an oil rotary pump may be used depending on the degree of vacuum. However, depending on the volume of the decompression chamber, or shortening of the vacuum sweep time or P For the purpose of further shortening the removal time, a mechanical booster pump, an oil diffusion pump, a turbo molecular pump, or the like may be provided.

The crucible disposed in the decompression chamber may be any material as long as it does not react with silicon to generate gas, and the crucible itself is hardly melted under reduced pressure. A material such as Si ₃ N ₄ can be used, but a graphite crucible having high purity (ash content of 10 ppm or less) and high density (bulk density of 1.8 g / cm ³ or more) is optimal. On the other hand, a quartz crucible generally used as a crucible for holding a molten silicon reacts with silicon under a high vacuum to generate SiO gas, and the high vacuum cannot be maintained. The gas that rises may cause problems such as bumping, and is not suitable for silicon purification by the vacuum melting method.

  Furthermore, as for the heating means for heating the silicon in the crucible, it is sufficient that the silicon in the crucible can be heated to a melting point or higher to form a molten silicon, for example, applying a voltage to a heating element such as graphite, A heater heating method may be used in which the molten silicon in the crucible is heated by the generated Joule heat. In addition, an induction coil is arranged outside the graphite crucible, and the graphite crucible is heated by an induced current, thereby the molten silicon It may be an induction heating system that heats. Any of these heating methods is a low-cost and simple heating method for metal dissolution that is widely used in general.

  The silicon purification apparatus of the present invention includes ripple induction means for increasing the liquid surface area of the molten silicon in the crucible in addition to the above-described decompression chamber, crucible, and heating means.

  As for the ripple inducing means, as long as ripples can be formed on the liquid surface of the silicon melt in the crucible, means for forming ripples by directly applying a force such as vibration to the silicon melt or the liquid surface, Any means such as a means for forming ripples by applying a force such as vibration to a crucible containing molten silicon is not particularly limited. For example, preferably, the decompression chamber is partitioned. A support shaft that is disposed so as to be able to move up and down through the wall to be moved, and is attached to the vicinity of the liquid surface of the silicon melt inside the wall at one end of the support shaft, thereby causing ripples on the liquid surface of the silicon melt And a ripple forming device having a ripple forming element and a driving means attached to the outside of the wall body on the other end side of the support shaft and applying vertical vibrations to the ripple forming element through the support shaft. More preferably, the ripple shape Child has a disc located at the liquid surface near the liquid silicon melt, it may be between a vibration device the drive means for imparting a vertical vibration to the support shaft.

  Preferably, the ripple forming device is provided with a support shaft lifting device that holds the support shaft so as to be movable in the vertical direction, and the support shaft is moved up and down by the support shaft lifting device to form ripples in the decompression chamber. It is preferable to move the child in the vertical direction, so that the ripple former can be accurately positioned in the vertical direction with respect to the liquid surface of the molten silicon, and the ripple means is given vertical vibration by the driving means. In this case, ripples can be efficiently formed on the surface of the molten silicon.

In the present invention, preferably, in addition to the ripple inducing means for increasing the liquid surface area of the molten silicon, a stirring means for the molten silicon is additionally provided.
Any stirring means may be used as long as the molten silicon contained in the crucible can be stirred to improve the diffusion rate of P in the molten silicon. For example, the decompression chamber is preferably defined. A rotating shaft that is rotatably disposed through the wall body, a stirrer that is attached to the inner end of the wall body of the rotating shaft and is formed in a silicon melt, and the like, and a wall of the rotating shaft A stirrer that is attached to the outside of the body and includes a rotational drive device that imparts forward and / or reverse rotational motion to the stirrer via a rotating shaft, and a wall that partitions the decompression chamber. Preferably, the tip end portion which is arranged to be movable up and down and is inserted into the silicon melt has one or a plurality of gas jet holes at the tip and / or the peripheral wall, and the inert gas is supplied from the gas jet holes to the silicon melt. Erupt inside It can be given a stirring device or the like provided with an inert gas inlet tube for agitating the silicon melt.

  When this silicon melt stirring means is constituted by a stirring device provided with a rotating shaft, a stirrer and a rotation driving device, preferably, the stirring shaft is shared with the support shaft of the ripple forming device as the rotating shaft of the stirring device. The stirrer is attached to the tip of the rippler provided on the support shaft, the rippler of the rippler is positioned in the liquid near the surface of the molten silicon, and the stirrer of the stirrer is It is preferable that the silicon melt is positioned deep in the liquid of the silicon melt, and in the case of a stirrer equipped with an inert gas introduction pipe, the support shaft of the ripple forming device is formed of a hollow pipe material and its tip and / or Alternatively, it is preferable to provide one or a plurality of gas ejection holes on the peripheral wall so that the support shaft of the ripple forming device can be used as an inert gas introduction pipe of the stirring device.

  In the present invention, preferably, in addition to the ripple inducing means for increasing the liquid surface area of the molten silicon, an impurity trapping means for capturing impurities evaporated from the liquid surface of the molten silicon is provided. This impurity trapping means may be provided separately from the stirring means, or may be provided together with the stirring means.

  The impurity trapping means may be basically an impurity trapping device having an impurity condensing part having a steam cooling surface for cooling and condensing impurity vapor evaporating from the liquid surface of the molten silicon. The impurity condensing part provided with a cooling surface may be a flat plate shape, a cylindrical shape, a coil shape, or the same or different materials and stacked with a space between them to ensure a wide steam cooling surface. The impurity condensing part may have a cooling structure that cools the steam cooling surface by preferably circulating a coolant such as water inside and / or outside of the impurity condensing part. It is good to be.

  In order to operate the silicon refining process continuously or intermittently when the impurity trapping means is mounted, it is preferable that the processing chamber and the opening / closing door accommodate the crucible in the chamber by a gate valve capable of opening / closing the decompression chamber. In addition to the impurity condensing unit, the impurity trapping device includes a condensing unit lifting device that holds the impurity condensing unit movably between the processing chamber of the decompression chamber and the preparatory chamber. And during the operation of the silicon refining process, the impurity condensing part is located in the processing chamber to capture impurities evaporating from the surface of the molten silicon, and before and / or after the silicon refining process operation, the impurity condensing part May be placed in the preparation chamber to perform pre-preparation and / or post-treatment of the silicon purification process. And the raising / lowering operation of this impurity condensing part can be performed simultaneously with the raising / lowering operation of said ripple formation apparatus, a stirring apparatus, or an inert gas introduction pipe | tube, or separately. By configuring in this way, the impurity condensing part can be cleaned without breaking the vacuum in the processing chamber during continuous operation or intermittent operation, and continuous operation or intermittent operation can be performed efficiently.

  In the present invention, the silicon refining process is continuously performed on the support shaft and the ripple forming element of the ripple forming device, the rotation shaft of the stirring device (the support shaft in the case of sharing with the support shaft of the ripple forming device) and the stirring piece. Even if the operation is performed intermittently or intermittently, it is not always necessary to divide the decompression chamber into the processing chamber and the preparation chamber and raise the preparation chamber before and / or after the operation of the silicon purification treatment. When the decompression chamber is divided into a processing chamber and a preparation chamber for the continuous or intermittent operation of the silicon purification process by mounting the impurity trapping means, preferably, the support shaft of the ripple forming device is connected to the stirring device. The rotation shaft is shared, and the ripple forming device of the ripple forming device and the stirring device of the stirring device are provided on the support shaft, and the support shaft, the ripple forming device and the stirring device are connected to the processing chamber by the support shaft lifting device of the ripple forming device. And the preparation room The support shaft, the ripple former and the stirrer are positioned in the processing chamber during the silicon purification process, and before and / or after the silicon purification process, the support shaft and ripple formation are performed. The child and stirrer may be retracted into the preparation chamber, which makes it easy to design the setting position of the gate valve that partitions between the processing chamber and the preparation chamber during continuous operation or intermittent operation, and Operation is also easy. The setting position of the support shaft of the ripple forming device and / or the rotation shaft of the stirring device need not be the same as the setting position of the impurity trapping device. It is also possible to set the support shaft and / or the rotation shaft of the stirring device. When the support shaft of the ripple forming device and / or the rotation shaft of the stirring device are set at different positions, it is not necessary to provide a special chamber partitioned by a gate valve for them.

  In the present invention, when removing impurities mainly composed of phosphorus in silicon using the silicon purification apparatus as described above, the pressure in the vacuum chamber is about 500 Pa or less and about 0.01 Pa depending on the apparatus configuration of the silicon purification apparatus used. Preferably, the pressure in the crucible is reduced to 100 Pa or less, more preferably 10 Pa or less to 0.1 Pa, and the silicon in the crucible is heated to its melting point, preferably 1600 ° C. to 1800 ° C. and melted. Impurities such as P are removed while forming ripples of a predetermined size on the surface of the molten silicon. When the pressure in the decompression chamber exceeds 500 Pa, a sufficient P removal rate cannot be obtained. On the other hand, in order to realize a pressure of less than 0.01 Pa, there arises a problem that the decompression equipment becomes expensive. Also, with respect to the heating temperature, silicon purification cannot be performed by a vacuum melting method below the melting point, and conversely, when the temperature is higher than 1800 ° C., the amount of silicon evaporation increases, and the yield of purified silicon obtained decreases. Moreover, the problem that the lifetime of a crucible falls arises.

  According to the silicon purification apparatus and the purification method of the present invention, by forming a predetermined ripple on the liquid surface of the molten silicon in the crucible, the liquid surface area of the molten silicon without increasing the opening area of the crucible opening. Since the evaporation of impurities such as P from the surface of the molten silicon can be greatly promoted without increasing the amount of heat released from the crucible opening, the same shape and size can be achieved. If it is the crucible, the removal rate of impurities such as P can be improved according to the size of the liquid surface area formed on the liquid surface of the molten silicon in the crucible.

  Hereinafter, preferred embodiments of the present invention will be specifically described based on the embodiments and examples shown in the accompanying drawings.

[First Embodiment]
In FIG. 1, the conceptual diagram of the silicon refinement | purification apparatus which concerns on the 1st Embodiment of this invention is shown. This silicon purification apparatus basically includes a decompression chamber 1 which is provided with a vacuum pump (decompression means) 5 and can be decompressed to a predetermined degree of vacuum, and a silicon melt 6 which is disposed in the decompression chamber 1 and accommodates therein. Made of high purity (ash content 10 ppm or less) and high density (bulk density 1.8 g / cm ³ or more) graphite crucible 2 and high purity high density graphite for heating silicon melt 6 in the crucible 2 A high-purity and high-density graphite support shaft 4a penetrating through a wall 1a defining the decompression chamber 1 through a vacuum seal 7 so as to move up and down, and one end of the support shaft 4a A high-purity, high-density disc (ripple former) 4b attached in the liquid near the liquid surface of the silicon melt 6 inside the wall 1a on the side, and outside the wall 1a on the other end of the support shaft 4a It has a vibration device (drive means) 4c that is attached and applies vertical vibration to the disk 4b via the support shaft 4a. And a ripple forming device (ripple inducing means) 4.

  In the first embodiment, the crucible 2 has a size of an outer diameter of 1000 mm × an inner diameter of 900 mm × an inner dimension depth of 700 mm, and the outside is covered with a heat retaining device 8 made of a carbon heat insulating material. A heater 3 is disposed between the outside of the crucible 2 and the inside of the heat retaining device 8 so as to cover the side road surface of the crucible 2. Further, the disk 4b of the ripple forming device 4 has a diameter of 100 mm, and when a vertical vibration having a predetermined amplitude Am is applied by the vibration device 4c, as shown in FIG. A ripple having a predetermined amplitude Wa is formed.

  In the first embodiment, the disk 4b of the ripple forming apparatus 4 is subjected to 2. under the conditions of a degree of vacuum of the decompression chamber 1 of 1 Pa, a heating temperature of the molten silicon 6 of 1700 ° C. and a frequency of 100 Hz applied to the disk 4b by the vibration device 4c. A vertical vibration with an amplitude Am of 5 mm, 5.0 mm, or 7.5 mm is applied, and the P removal rate from the molten silicon 6 at each amplitude Am is obtained by ICP emission analysis. The amplitude Am is 5.0 mm. The relative value when the amplitude Am was 2.5 mm and 7.5 mm was obtained with the P removal rate of 1 as the time, and the relative relationship of the P removal rate with respect to the amplitude Am was examined. The results are shown in FIG.

  As is apparent from the results of FIG. 3, it can be seen that the P removal rate from the molten silicon 6 is substantially proportional to the amplitude Am of the vertical vibration applied to the disk 4b by the vibration device 4c. In order to stably form ripples with the disk 4b, the amplitude Am of the vertical vibration is up to about twice the wavelength λ to be generated. Less than 1 times, the effect can not be expected.

[Second Embodiment]
In FIG. 4, the conceptual diagram of the silicon refinement | purification apparatus which concerns on the 2nd Embodiment of this invention is shown. As in the case of the first embodiment shown in FIG. 1, the silicon purification apparatus includes a decompression chamber 1 provided with a vacuum pump 5, a crucible 2 in which a silicon melt 6 is accommodated, and silicon in the crucible 2. A heater 3 for heating the molten metal 6, a support shaft 4a penetrating through the wall 1a defining the decompression chamber 1 through a vacuum seal 7 so as to be movable up and down, and silicon inside the wall 1a at one end of the support shaft 4a A disk 4b attached in the liquid near the liquid surface of the molten metal 6, and a vibration device attached to the outside of the wall 1a at the other end of the support shaft 4a and applying vertical vibration to the disk 4b via the support shaft 4a. Unlike the case of the first embodiment shown in FIG. 1, the support shaft 4a is formed of a hollow pipe material, and a gas ejection hole 9b is formed at the lower end thereof. And inside the molten silicon 6 from the outside of the decompression chamber 1 through the support shaft 4a. A stirring device (stirring means) 9 including an inert gas introduction pipe 9a for introducing the inert gas 9 and stirring the molten silicon 6 with the inert gas 9c introduced into the molten silicon 6 is provided. The ripple forming device 4 also serving as the stirring device 9 moves the ripple forming device 4, the support shaft 4 a of the stirring device 9, and the disk 4 b of the ripple forming device 4 in the vertical direction, and the disc 4 b in the silicon melt 6 and A position adjusting device 10 for adjusting the vertical position of the gas ejection hole 9b is provided.

  According to the silicon refining device of the second embodiment, ripples can be formed on the liquid surface of the molten silicon 6 in the crucible 2 by the ripple forming device 4 as in the case of the first embodiment. The liquid surface area of the molten silicon 6 can be increased to promote the evaporation of impurities such as P from the molten metal 6 and the inert gas 9c is ejected from the gas ejection hole 9b at the lower end of the support shaft 4a by the stirring device 9. By doing so, the inside of the silicon melt 6 can be stirred, the diffusion rate of impurities such as P in the silicon melt 6 can be improved, and the removal rate of impurities such as P can be further improved.

[Third Embodiment]
In FIGS. 5-7, the conceptual diagram of the silicon | silicone refinement | purification apparatus which concerns on the 3rd Embodiment of this invention is shown. As in the case of the first embodiment shown in FIG. 1, the silicon purification apparatus includes a decompression chamber 1 provided with a vacuum pump 5, a crucible 2 in which a silicon melt 6 is accommodated, and silicon in the crucible 2. A heater 3 for heating the molten metal 6 and a ripple forming device 4 are provided.

  In the third embodiment, as in the case of the first embodiment, the ripple forming device 4 includes a support shaft 4a penetrating the wall body 1a of the decompression chamber 1 in a vertically movable manner, and the support shaft 4a. A disc 4b attached in the liquid near the liquid surface of the silicon melt 6 inside the wall 1a on one end side, and attached to the outside of the wall 1a on the other end side of the support shaft 4a, and the disc via the support shaft 4a Unlike the case of the first embodiment, the support shaft 4a used as the rotation shaft 9a and the disk 4b of the support shaft 4a (9a) are provided. Is also attached to the tip side and is placed on the outside of the wall 1a on the other end side of the support shaft 4a and imparts rotational motion to the support shaft 4a. A stirring device 9 for the molten silicon 6 having a rotation driving means is attached, and the ripple forming device 4 Drive device 4c having both functions (9e) is provided as a rotation driving means of the vibrating means and a stirrer 9. Further, in the silicon refining device of the third embodiment, the detachable liquid surface heat retaining portion 8a that heats the silicon molten metal 6 so as to cover the upper portion of the liquid surface peripheral portion of the silicon molten metal 6 in the crucible 2 with the heat retaining device 8. Is attached.

  In the third embodiment, the decompression chamber 1 is divided into a processing chamber 1b for accommodating the crucible 2 and a preparation chamber 1c having an opening / closing door 12 by a gate valve 11 that can be opened and closed. The processing chamber 1b and the preparation chamber 1c are provided with vacuum pumps 5a and 5b, respectively, the support shaft 4a (9a) of the ripple forming device 4 and the stirring device 9, the disk 4b of the ripple forming device 4 and the stirring. A support shaft lifting / lowering device 13 is provided to hold the stirring blade 9d of the apparatus 9 so as to be movable between the processing chamber 1b and the preparation chamber 1c, whereby the support shaft 4a, The disk 4b and the stirring blade 9d are positioned at predetermined positions in the processing chamber 1b to form ripples on the molten silicon 6 and stir the molten silicon 6, and before and / or after the operation of the silicon refining treatment, Prepare the support shaft 4a, disk 4b and stirring blade 9d. And is configured so that it can by positioned in the chamber 1c performs preparatory and / or post-treatment of the silicon purification process.

  Further, in the decompression chamber 1, an impurity trapping device (impurity) is located above the opening 2a of the crucible 2 and cools, condenses and traps the impurity vapor of impurities such as P rising from the opening 2a. (Capturing means) 14 is provided. The impurity trapping device 14 includes an impurity condensing unit 15 formed in a cylindrical shape having a slightly larger inner diameter than the opening 2a of the crucible 2 by a hollow wall material, and the impurity condensing unit 15 as a processing chamber 1b of the decompression chamber 1 And a condensing unit lifting / lowering device 16 that is movably held between the first and second preparation chambers 1c, and the impurity condensing unit 15 has a vapor cooling surface 17 formed on the inner surface of the inner wall thereof and an upper portion thereof. Is provided with a refrigerant pipe 18 for introducing a refrigerant 19 such as water into the hollow portion of the hollow wall material to cool the steam cooling surface 17, thereby allowing the impurity condensing part 15 to be connected to the treatment chamber during the silicon purification process. Impurities such as P evaporating from the liquid surface of the molten silicon 6 are captured at a predetermined position in 1b, and the impurity condensing unit 15 is provided in the preparation chamber 1c before and / or after the operation of the silicon purification process. Pre-preparation and / or silicon purification process And it is configured so as to perform post-processing.

  Therefore, according to the silicon purification apparatus of the third embodiment, during the operation of the silicon purification process, the inside of the processing chamber 1b and the preparation chamber 1c are depressurized to a predetermined degree of vacuum by the vacuum pump 5, and the heater 3 is used. The molten silicon 6 is heated to a predetermined temperature, and after the silicon is melted, the gate valve 11 is opened to allow communication between the processing chamber 1b and the preparation chamber 1c. As shown in FIGS. 13 is operated to lower the support shaft 4a (9a) of the ripple forming device 4 and the stirring device 9, the disk 4b of the ripple forming device 4 and the stirring blade 9d of the stirring device 9, and the disk 4b is molten silicon in the processing chamber 1b. 6 is positioned in the liquid near the liquid surface, and the stirring blade 9d is positioned in the liquid of the silicon melt 6 below the disk 4b. The impurity condensing part 15 is lowered and the processing chamber 1b The impurity condensing part 15 is located above the opening 2a of the crucible 2 so that the impurity vapor of impurities such as P rising from the opening 2a can be cooled and condensed by the vapor cooling surface 17, and supplemented. The silicon purification process is performed.

  According to the third embodiment, ripples are formed by driving the drive device 4c (9e) and applying predetermined vertical vibration and rotational motion to the support shaft 4a (9a) of the ripple forming device 4 and the stirring device 9. The disk 4b of the apparatus 4 vibrates up and down in the liquid near the liquid surface of the molten silicon 6 to form ripples on the liquid surface of the molten silicon 6 to increase the surface area of the liquid and improve the evaporation rate of impurities such as P. Further, since the stirring blade 9d of the stirring device 9 rotates in the silicon melt 6 to improve the diffusion rate of impurities such as P in the silicon melt 6, P in silicon by the vacuum melting method of silicon, etc. The impurity removal rate, particularly the P removal rate, is greatly improved.

  After the operation of the silicon refining process is completed, as shown in FIG. 7, the support shaft lifting device 13 is operated to support the ripple forming device 4 and the support shaft 4a (9a) of the stirring device 9, and the disc 4b of the ripple forming device 4. The stirring blade 9d of the stirring device 9 is raised and accommodated in the preparation chamber 1c, and the impurity condensing unit 15 of the impurity trapping device 14 is raised by operating the condensing unit lifting / lowering device 16 and accommodated in the preparation chamber 1c. Next, after closing the gate valve 11 again to shut off the space between the processing chamber 1b and the preparation chamber 1c, the inside of the preparation chamber 1c is returned to atmospheric pressure, and in this state, the open / close door 12 is opened to enter the preparation chamber 1c. Post-treatment of silicon purification treatment such as cleaning and repairing of the support shaft 4a (9a), the disk 4b and the stirring blade 9d, the impurity condensing unit 15 of the impurity trapping device 14, etc. of the contained ripple forming device 4 and stirring device 9 To prepare for the next silicon purification process.

  Thus, by preparing the preparatory chamber 1c in the decompression chamber 1 and performing the pre-treatment and / or post-treatment of the silicon purification treatment in the preparatory chamber 1c, continuous operation can be performed particularly in the treatment chamber 1b of the decompression chamber 1. Therefore, it becomes an industrially extremely useful silicon purifier.

[Example 1]
In the apparatus configuration of the third embodiment, a graphite crucible 2 having an outer diameter of 1000 mm, an inner diameter of 900 mm, and an inner depth of 700 mm is used, and the heater 3 can be supplied with a maximum of 300 kW. As the ripple forming device 4, a support shaft 4a having a length of 1500 mm and a disk 4b having a diameter of 100 mm is used, and as the stirring device, a stirring blade 9d has two blades and a rotating diameter of 300 mm. And the distance between the disk 4b and the stirring blade 9d is set to 500 mm, and the depth of the stirring blade 9d in the silicon melt 6 is set to 500 mm. For the liquid level 6 (as a flat state without ripples), the area ratio of covering the crucible opening by the liquid level thermal insulation 8a of the thermal insulation device 8 was set to 80%.

The crucible 2 was charged with 900 kg of raw silicon having an initial P concentration of 30 ppm, the pressure in the decompression chamber 1 (processing chamber 1b) was reduced to a vacuum of 5.0 Pa or less, and then the heater 3 was energized to melt the raw silicon. The silicon refining treatment was performed by adjusting the amplitude of vertical vibration of the disk 4b to 2.5 mm and the rotation speed of the stirring blade 9d to 30 rpm and maintaining the vacuum at 1 Pa and 1700 ° C. for 12 hours under the conditions of the molten silicon 6 .
For this silicon purification treatment, the vibration by the disk 4b, the rotation by the stirring blade 9d, and the heat insulation by the liquid surface heat retaining part 8a are set as three parameters. And the P removal rate was evaluated. The results are shown in Table 1.

  As is apparent from the results shown in Table 1, in Comparative Example 1 in which neither vibration nor rotation was given, the processing speed was 1.4 times in the present invention example 1 in which only vibration was given, and the rotation In the present invention example 2 to which vibration was applied, the treatment speed was 5.5 times, and in the present invention example 3 to which rotation and heat retention were given, the treatment speed was 4.0 times, and furthermore, In Example 4 of the present invention in which heat retention was combined with rotation and vibration, the processing speed was 15 times that of Comparative Example 1.

[Example 2]
In the apparatus configuration of the third embodiment, 900 kg of raw silicon is used, and purification is performed under the same conditions (1 Pa, 1700 ° C., 12 hours) as in Example 1 of the present invention. In addition, when the impurity is condensed by the impurity trapping device 14 (with or without impurity condensation) and when the impurity condensing unit 15 is cleaned with or without impurity condensing (with or without condensing unit cleaning) Silicon purification treatment was performed in three cases, and the P removal rate was evaluated. In Invention Example 6, the impurity condensing part 15 was cleaned every 2 hours. The results are shown in Table 2.

  As is apparent from the results shown in Table 2, the P removal rate is about 2.4 in the case of the present invention example 5 in which only the impurity condensation is performed, compared with the case of the present invention example 2 in which the impurity condensation is not performed. In addition, in the case of the present invention example 6 in which the condensation part cleaning was performed in addition to the impurity condensation, the P removal rate was increased by about 5.1 times.

  According to the silicon purification apparatus and the purification method of the present invention, the P removal rate is remarkably increased using industrially practical equipment and heating means without using costly equipment or special heating means such as an electron beam. Impurities can be improved and impurities such as P in the raw material silicon can be separated and removed industrially easily and inexpensively, so that high-purity silicon suitable for applications such as solar cells is produced industrially advantageously. can do.

FIG. 1 is an explanatory view conceptually showing a silicon purification apparatus according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining a liquid surface state of the silicon melt in the crucible of FIG. 1.

FIG. 3 is a graph showing the relative relationship between the disk amplitude Am and the P removal speed of the ripple forming apparatus in the first embodiment. FIG. 4 is an explanatory view conceptually showing the silicon purification apparatus according to the second embodiment of the present invention.

FIG. 5 is an explanatory diagram conceptually showing a silicon purification apparatus according to the third embodiment of the present invention. FIG. 6 is an explanatory diagram for explaining a liquid surface state of the silicon melt in the crucible of FIG. 4.

FIG. 7 is an explanatory diagram conceptually showing a state during pre-processing and / or post-processing of the silicon purification process in the silicon purification apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Decompression chamber, 1a ... Wall body, 1b ... Processing chamber, 1c ... Preparation chamber, 2 ... Crucible, 2a ... Opening, 3 ... Heater (heating means), 4 ... Ripple formation device (ripple induction means), 4a, 9a ... support shaft, 4b ... disc (ripple former), 4c ... vibration device (drive means), 5,5a, 5b ... vacuum pump (pressure reduction means), 6 ... silicon melt, 7 ... vacuum seal, 8 ... heat retention device , 8a ... Liquid temperature retaining part, Wa ... Ripples, 9 ... Stirring device (stirring means), 9a ... Inert gas introduction pipe, 9b ... Gas ejection hole, 9c ... Inert gas, 4c (9e) ... Drive device, 9d DESCRIPTION OF SYMBOLS ... Stirring blade, 10 ... Position adjusting device, 11 ... Gate valve, 12 ... Opening / closing door, 13 ... Support shaft raising / lowering device, 14 ... Impurity trapping device (impurity trapping means), 15 ... Impurity condensing part, 16 ... Condensing part lifting / lowering device , 17 ... Steam cooling surface, 18 ... Refrigerant piping, 19 ... Refrigerant.

Claims (9)

  A decompression chamber decompressed to a predetermined pressure or less by a decompression means, a crucible disposed in the decompression chamber and containing silicon, and a heating means for heating the silicon in the crucible, and heating the silicon under reduced pressure In the silicon refining apparatus for evaporating and separating and removing impurities in the generated molten silicon, the silicon purifying is characterized by comprising ripple inducing means for increasing the liquid surface area of the molten silicon apparatus.   The support shaft in which the ripple inducing means is arranged to move up and down and / or rotate through the wall defining the decompression chamber, and near the liquid surface of the silicon melt inside the wall at one end of the support shaft And a ripple former that forms ripples on the surface of the molten silicon, and is attached to the outside of the wall body at the other end of the support shaft, and is vertically oscillated and / or rotated to the ripple former via the support shaft. 2. The apparatus for purifying silicon according to claim 1, wherein the apparatus is a ripple forming apparatus having a driving means for imparting motion.   3. The silicon purification apparatus according to claim 2, wherein the driving means applies a vertical vibration to the support shaft, and the ripple former is a disk located in the liquid near the liquid surface of the molten silicon.   The silicon purifier according to any one of claims 1 to 3, wherein a stirring means for the molten silicon is provided in addition to the ripple inducing means for increasing the liquid surface area of the molten silicon.   The stirring means is attached to the support shaft of the ripple forming device on the tip side of the ripple forming element and is located in the silicon melt, and the rotation that imparts forward and / or reverse rotational motion to the support shaft. The silicon purifier according to claim 4, which is a stirring device having a driving device.   The silicon purification according to any one of claims 1 to 5, wherein an impurity trapping means for trapping impurities evaporating from the liquid surface of the molten silicon is provided in addition to the ripple inducing means for increasing the liquid surface area of the molten silicon. apparatus.   The silicon purifier according to claim 6, wherein the impurity trapping means is an impurity trapping device including an impurity condensing unit having a vapor cooling surface for cooling and condensing the impurity vapor evaporated from the liquid surface of the molten silicon.   The decompression chamber is divided into a processing chamber that accommodates the crucible in the chamber by a gate valve that can be opened and closed, and a preparation chamber that includes an opening / closing door, and the impurity trapping device divides the impurity condensing portion and the impurity condensing portion into the processing chamber of the decompression chamber. And a condensing unit lifting / lowering device that is movably held between the chamber and the preparation chamber. During the operation of silicon purification, the impurity condensing unit is located in the processing chamber to capture impurities that evaporate from the surface of the molten silicon Further, before and / or after the operation of the silicon purification treatment, the silicon purification apparatus according to claim 7, wherein the impurity condensing part is located in the preparation chamber to perform the preparation and / or post-treatment of the silicon purification treatment. .   A silicon purification method for removing impurities mainly composed of phosphorus in silicon using the silicon purification apparatus according to any one of claims 1 to 8, wherein the pressure in the vacuum chamber is reduced to 500 Pa or less and the melting point of silicon in the crucible is reduced. A method for purifying silicon characterized in that it is heated and melted as described above, and at the same time, ripples are formed on the liquid surface of the molten silicon in the crucible by means of ripple inducing means while removing phosphorus-based impurities.

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