JP2013035712A - Method and apparatus for producing silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing silicon, by which high-purity silicon material can be obtained which cannot be obtained just by sintering silicon powder through a spark plasma sintering method, from the silicon powder that contains impurities such as carbon and oxygen.SOLUTION: The method includes: steps S02 to S04 of sintering the silicon powder through the spark plasma sintering method; and steps S11 to S12 of melting the silicon powder thus sintered, in a chamber, thereby producing a melt of high-purity silicon material, for example, a melted silicon having an impurity concentration reduced to the ppm order.

Description

  The present invention relates to a technique for obtaining a high-purity silicon material from silicon powder generated from a silicon wafer manufacturing process.

  When a semiconductor chip or a wafer serving as a base material for a solar cell is cut out from a silicon ingot using a slicing device such as a wire saw or a band saw, a large amount of silicon sludge (swarf) is generated that accounts for about 40% of the weight of the silicon ingot. To do. At present, some of this silicon sludge is sometimes used as a deoxidizer, but most of it is incinerated and disposed of as landfill without being reused.

  In recent years, with increasing awareness of the environment, the importance of recycling silicon sludge, which is currently treated as waste, is increasing from the viewpoint of effective use of limited resources. If silicon sludge can be recycled, it can greatly contribute to the stable supply of silicon materials to the rapidly growing solar cell industry and the cost reduction of solar cells.

  However, silicon sludge discharged from a silicon ingot slicing apparatus is dispersed in a working fluid (coolant) used during slicing. In order to recover this and return it to high-purity silicon, it is necessary to separate only the silicon sludge from the processing liquid by means such as centrifugation and then dry it, and to remove impurities from the dried silicon sludge. Various treatments for removing impurities have hindered the profitability of mass production practicality.

  As a means for solving this problem of profitability, Patent Document 1 proposes a method using a discharge plasma sintering apparatus as a prior example. This preceding example is a method of processing silicon powder obtained by drying silicon sludge recovered from a working fluid (coolant) into a high-purity silicon material using a discharge plasma sintering apparatus. The outline of this precedent case will be described below with reference to FIG.

The silicon powder separated from the processing liquid and dried has an oxide film (SiO ₂ ) formed on the surface to become an oxide. Therefore, it is not possible to obtain a high-purity silicon material simply by sintering silicon powder.

  Therefore, in the preceding example, as shown in FIG. 8, the silicon powder 8 as the starting raw material is filled in the sintering die 6 and the inside of the vacuum chamber 9 is evacuated, and then the upper punch 4 and A pulse current is supplied from the pulse power source 1 to the upper punch 4 and the lower punch 5 through the upper punch electrode 2 and the lower punch electrode 3 while applying a pressure P to the lower punch 5 from above and below. In this way, Patent Document 1 describes that an oxidation-reduction reaction occurs and high-purity silicon can be easily obtained.

  The upper punch electrode 2 and the lower punch electrode 3 generate heat at the same time as the current flows, so that the temperature rise is prevented by cooling with the vacuum chamber 9 while the current is flowing.

  Moreover, in this precedent example, SPS-520 made by SPS Shintex Co., Ltd. is used as the discharge plasma sintering apparatus, and the sintering die 6 having an inner diameter of about 20 mm and a height of 40 mm is used. A carbon sheet having a thickness of 0.2 mm is used for peeling the sintered die 6 and the silicon powder 8. At the time of sintering, with the silicon powder 8 being pressed through the upper punch 4 and the lower punch 5, a pulse current is further supplied to raise the temperature of the sintering die 6 to 800 ° C., hold it for 5 minutes, and then turn off the current. Cooling. The degree of vacuum in the vacuum chamber 9 during sintering is about 3 Pa.

  As described above, as a technique for recycling the silicon powder generated from the silicon wafer manufacturing process, a method for obtaining a high-purity silicon material by sintering the silicon powder by the discharge plasma sintering method has been proposed. .

JP 2008-247670 A

  However, the sintered silicon material obtained by the conventional method has a purity that does not cause any problem as long as it is reused as a deoxidizer or an alloy raw material. It is not pure enough to be used as a raw material for silicon. For example, in order to use it as a raw material of polysilicon, the concentration of impurities (for example, carbon and oxygen) remaining in the silicon material needs to be on the order of ppm.

  The present invention relates to a silicon manufacturing method and a silicon manufacturing apparatus capable of obtaining a high-purity silicon material that cannot be achieved from silicon powder containing impurities such as carbon and oxygen by only sintering it by a discharge plasma sintering method. The purpose is to provide.

  In order to achieve the above object, the silicon production method of the present invention sinters silicon powder in a container by a discharge plasma sintering method, and then flows the silicon powder in the container by passing an electric current through the container. It is characterized by melting to produce molten silicon.

  In order to achieve the above object, the silicon manufacturing apparatus of the present invention includes a container, a punch for pressurizing the contents of the container, a power source for flowing a current through the container, an operation of the punch, and the power source. A control device for controlling the operation of the apparatus, and under the control of the control device, the silicon powder in the container is pressurized with the punch, and a current is passed from the power source to the container to sinter the silicon powder. Then, an electric current is supplied from the power source to the container, and the sintered silicon powder is melted to generate molten silicon.

  According to the present invention, it is possible to obtain a high-purity silicon material that cannot be achieved from silicon powder containing impurities such as carbon and oxygen by simply sintering it by a discharge plasma sintering method. In particular, when silicon powder generated from a silicon wafer manufacturing process is used as a starting raw material, a high-purity silicon material in which the impurity content is reduced to the ppm order can be obtained.

The figure which shows schematic structure of the silicon | silicone recycling apparatus in embodiment of this invention. Diagram showing the relationship between the graphite mold temperature and the amount of displacement in the punch indentation direction when using the spark plasma sintering method The figure which shows the relationship between the graphite type temperature and pulse current in embodiment of this invention Flowchart of silicon manufacturing method in the embodiment of the present invention Flow chart of spark plasma sintering method (A) External view showing the positional relationship before sintering of the graphite mold and punch in the embodiment of the present invention, (b) External appearance showing the positional relationship of the graphite mold and punch in the embodiment of the present invention during sintering Figure, (c) External view showing the positional relationship when the graphite mold and the punch are melted in the embodiment of the present invention (A) Cross-sectional view showing the positional relationship before sintering of the graphite mold and punch in the embodiment of the present invention, (b) Cross section showing the positional relationship during sintering of the graphite mold and punch in the embodiment of the present invention FIG. 4C is a sectional view showing the positional relationship when the graphite mold and the punch are melted in the embodiment of the present invention The figure which shows the discharge plasma sintering apparatus of patent document 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the same components may be denoted by the same reference numerals, and redundant description may be omitted. In addition, the drawings schematically show each component as a main component for easy understanding. In addition, the thickness, length, and the like of each of the illustrated components are different from the actual for convenience of drawing. In addition, the numerical value shown by the following embodiment is an example, and is not specifically limited, A various change is possible in the range which does not deviate substantially from the effect of this invention.

  First, the spark plasma sintering (SPS method) will be briefly described.

  One of the conventional sintering methods is a hot press method. The hot press method is a sintering method in which heat is applied to a powder while applying pressure to sinter. The spark plasma sintering method, like the hot press method, is a sintering method in which heat is applied to the powder while applying pressure to sinter, but the powder is heated using a pulse current to heat the powder. It differs from the hot press method in that discharge plasma is generated at the mutual contact part.

  In the spark plasma sintering method, a powder is filled in a graphite female mold (graphite mold), and then pressure is applied to the powder filled in the female mold with a male mold called a punch. Apply front and rear pulse voltage. This pulse voltage causes a current of several hundred amperes or more to flow in the form of pulses at microsecond intervals, thereby causing the female die itself to generate heat, and directly applying a pulse current to the powder inside the female die to bring the powder into contact with each other. Generates a spark discharge. Combined with the heat generated by the female mold itself, the thermal diffusion and electric field diffusion of the high energy (joule heat and electromagnetic energy) of the discharge plasma generated instantaneously by the spark discharge, the powder is bonded to the sintered body. Become.

  The reason why sintering is performed with a pulse current is to efficiently diffuse the current path between the powders by alternately repeating ON (application) and OFF of the current.

  According to the spark plasma sintering method, sintering can be performed in a temperature range as low as 200 ° C. to 500 ° C. in a super-high temperature region from a low temperature to 2000 ° C. or higher compared with a conventional method such as a hot press method. . Furthermore, according to the discharge plasma sintering method, the time until sintering including temperature rise and holding can be shortened by about 5 to 20 minutes as compared with a conventional method such as a hot press method. The spark plasma sintering method is also characterized in that a dense and homogeneous sintered body can be obtained because the crystal growth of the powder itself is suppressed because the time required for sintering is short.

  Subsequently, regarding the sintered body obtained by sintering the silicon powder recovered from the machining liquid with a discharge plasma sintering apparatus, the result of an experiment in which the content of impurities contained in the sintered body was examined will be described.

  As a result of measuring the carbon and oxygen contents before sintering for the silicon powder used as an experimental material by a combustion method, oxygen was 26.1% and carbon was 3.6%. Here, among the contents of carbon and oxygen, which are impurities, the oxygen amount is prominent and the silicon sludge recovered from the processing liquid is long in a state where it is left in the atmosphere after being squeezed by a filter press machine. Since it was stored for a long time, it is estimated that a natural oxide film was generated on the surface. Moreover, since the color of the surface of the silicon powder was reddish brown (rust color), it was confirmed that an oxide film was formed on the surface.

  After filling 2.3 g of this starting raw material silicon powder into a graphite mold (female mold) and lightly pressing and solidifying with a hand press machine, sintering is performed in a non-oxidizing atmosphere with a discharge plasma sintering apparatus. It was. The graphite mold has an inner diameter of 20 mm, an outer diameter of 50 mm, and a height of 40 mm. The size of the punch (made of graphite) is 20 mm in outer shape and 20 mm in length.

  FIG. 2 shows the relationship between the graphite mold temperature and the amount of displacement in the punch indentation direction when the discharge plasma sintering method is used. In FIG. 2, the black circle graph represents the graphite mold temperature [° C.], and the black square graph represents the displacement amount [mm] in the indentation direction of the punch. The horizontal axis represents the elapsed time [minutes]. Here, the graphite mold temperature is the temperature outside the mold of the graphite mold.

  As can be seen from FIG. 2, the amount of displacement in the pressing direction of the punch greatly changes before and after the time when the graphite mold temperature reaches 1100 ° C. (approximately 10.5 minutes to approximately 12 minutes). . This is considered to indicate that the powder filled in the graphite mold changed from the powder state to the sintered state. In this experiment, the graphite mold outer frame temperature was maintained at a temperature of about 1100 ° C. for about 5 minutes (elapsed time 11.5 minutes to elapsed time 16.5 minutes), and then cooled. When the cross section after sintering was observed, it became a gray metal color, and it was confirmed that it became a sintered body.

  As a result of analyzing the oxygen and carbon contents of the sintered body produced under the above conditions using the discharge plasma sintering method, the oxygen content was 3.9% and the carbon content was 3.2%. Although there was a decrease in oxygen, no significant decrease was observed in carbon. In order to reduce the content of oxygen and carbon, sintering was performed by changing the maintenance time of the graphite mold temperature 1100 ° C., which is a sintering temperature, from 5 minutes to 30 minutes. There was no significant difference in the content of oxygen and carbon after sintering.

  The above is an explanation of the discharge plasma sintering method.

  On the other hand, as described above, in order to return the sintered material to the ingot material, a method of obtaining a higher purity is required, and in the purity when simply sintered by the discharge plasma sintering method, It is insufficient. Specifically, as a high-purity ingot material, for example, it is necessary to reduce the impurity concentration to the ppm order.

  In the present embodiment, the impurity concentration is reduced to the ppm order. Hereinafter, this embodiment will be described.

  FIG. 1 shows an outline of an apparatus configuration for carrying out the silicon manufacturing method of the present embodiment. In the silicon manufacturing method of the present embodiment, the silicon powder 12 as a starting raw material is sintered by a discharge plasma sintering method in a non-oxidizing atmosphere, and then the sintered silicon powder (sintered body) is used. This is a method of melting in a graphite mold 11 to produce a high purity silicon material melt. Here, the graphite mold 11 is an example of a container. In the following description, a series of steps of the silicon manufacturing method of the present embodiment is controlled using a control device (not shown).

  FIG. 1 shows a schematic configuration of a silicon recycling apparatus (an example of a silicon manufacturing apparatus) in the present embodiment. As shown in FIG. 1, the silicon recycling apparatus of the present embodiment includes a graphite mold 11, a punch 13, and a pulse power source 17 for causing a pulse current to flow through the graphite mold 11. Then, using this silicon recycling apparatus, in a non-oxidizing atmosphere, the silicon powder 12 filled in the graphite mold 11 was pressed by the punch 13 while flowing a pulse current through the graphite mold 11 and sintered. Thereafter, a pulse current is further passed through the graphite mold 11 to melt the sintered silicon powder (sintered body) to produce a high-purity silicon material melt (hereinafter referred to as molten silicon).

  According to the present embodiment, an impurity concentration is obtained from silicon powder 12 containing impurities such as carbon and oxygen by flowing a pulse current through graphite mold 11 to melt the sintered silicon powder (sintered body). Can be obtained a high-purity silicon material reduced to the ppm order. By reducing the impurity concentration of the silicon material to the order of ppm, it becomes possible to supply a high-purity silicon material that can be used for the production of polysilicon as a raw material of the wafer.

  In the present embodiment, the molten silicon inside the graphite mold 11 is recovered by flowing outside through a runner (described later) formed in the graphite mold 11 under pressure. By doing in this way, molten silicon can be collected efficiently. In addition, it is thought that pressurizing while melting the silicon powder as in the present embodiment not only increases the efficiency of recovery of the molten silicon but also increases the purity of the molten silicon. .

  In the present embodiment, the sintered silicon powder (sintered body) is melted inside the graphite mold 11 filled with the silicon powder 12 as the starting raw material. In this way, it is not necessary to transfer to another container in order to melt the sintered body.

  In the present embodiment, the silicon powder 12 is sintered in the same graphite mold 11 by continuously applying a pulse current after the silicon powder 12 is sintered in the graphite mold 11 by the discharge plasma sintering method. It is continuously changed to molten silicon through the body. In this way, since the starting raw material can be changed to the melt at the same location, the processing time can be shortened.

  That is, in the present embodiment, a pulse current continues to flow even after the silicon powder 12 filled in the graphite mold 11 is in a sintered state by using a discharge plasma sintering apparatus. By changing from a powder sintered body to molten silicon, high-purity silicon materials from which the impurity concentration is removed to the order of ppm are manufactured. Further, by providing the graphite mold 11 with a runner through which the molten silicon flows, the molten silicon can be efficiently recovered. These will be described in further detail below.

  In the present embodiment, a graphite female type (graphite type 11) and male type (punches 13 and 14) were used as in the sintering experiment of the discharge plasma sintering method described above. Silicon powder 12 generated from the silicon wafer manufacturing process was used as the starting raw material to be filled in the graphite mold 11. The filling amount of the silicon powder 12 was 2.3 g, and the impurity content of the silicon powder 12 before sintering was 2.2% for oxygen and 5% for carbon.

  After filling the graphite mold 11 with the silicon powder 12, it was hardened with a hand press machine, sintered in a non-oxidizing atmosphere by the discharge plasma sintering method, and further pulsed.

  FIG. 3 shows the relationship between the graphite mold temperature and the pulse current in the present embodiment. In FIG. 3, the black circle graph represents the graphite mold temperature [° C.], and the black triangle graph represents the pulse current [A]. The horizontal axis represents the elapsed time [minutes]. The graphite mold temperature is the temperature outside the mold of the graphite mold.

  Compared with the sintering experiment using the discharge plasma sintering method (see FIG. 2), the silicon manufacturing method of the present embodiment maintains the temperature of the graphite mold 11 at about 1350 ° C. for about 10 minutes ( The difference is that after the elapsed time of about 14 minutes to the elapsed time of about 24 minutes, it is maintained at about 1450 ° C. for about 5 minutes (the elapsed time of about 28 minutes to the elapsed time of about 33 minutes).

  FIG. 4 is a flowchart showing the silicon manufacturing method in the present embodiment. FIG. 5 shows a flowchart when only the discharge plasma sintering method is used to clarify the difference between the silicon manufacturing method and the discharge plasma sintering method in the present embodiment.

  First, each step of the discharge plasma sintering method shown in FIG. 5 will be described. In addition, the general discharge plasma sintering apparatus was used for the discharge plasma sintering apparatus which implement | achieves the process shown in the flowchart of FIG.

  First, silicon powder, which is a starting raw material, is filled into a graphite mold (step S01 in FIG. 5). Then, the upper punch is pushed into the graphite mold and pressurized at 30 MPa and pulsed, and the graphite mold is heated to 1100 ° C. (step S02 in FIG. 5), and this state is maintained for 10 minutes (step S03 in FIG. 5). .

  By thus maintaining the pressure and pulse energization, the silicon powder in the graphite mold changes to a sintered body (step S04 in FIG. 5). The sintering is performed in a non-oxidizing atmosphere such as a vacuum.

  The temperature at the time of sintering is a temperature inherent to the starting raw material. In the case of silicon, a good sintered state can be obtained in a temperature range of 1000 ° C. to 1400 ° C. In the case of silicon, if the temperature is below 1000 ° C., sintering does not proceed sufficiently. If the sintering does not proceed sufficiently, the shape will be lost when taken out from the graphite mold, and silicon powder will remain inside the graphite mold, resulting in insufficient strength after sintering. On the other hand, when sintering is performed at a temperature higher than 1400 ° C., the state of silicon inside the graphite mold changes from a sintered state (solid) to a molten state, which makes it difficult to maintain the shape of the silicon after sintering. Become.

  When the sintering is completed, pressurization and pulse energization are stopped (step S05 in FIG. 5), the upper punch is moved upward, and the silicon material that has become a sintered body is taken out from the graphite mold (step S06 in FIG. 5). .

  As described above, the silicon material manufactured only by the discharge plasma sintering method is a sintered body, and thus has a stable shape without being out of shape, and can be easily transported and processed as compared with powder. However, oxygen and carbon, which are examples of impurities, have not greatly decreased from before sintering, and remain on the order of several percent. Such a silicon material containing a large amount of impurities cannot be used for semiconductors or solar cells. That is, the silicon material manufactured only by the discharge plasma sintering method cannot be used for semiconductors or solar cells.

  Subsequently, each step of the silicon manufacturing method shown in FIG. 4 will be described. In the present embodiment, a high-purity silicon material is manufactured by performing each step shown in FIG.

  The silicon recycling apparatus shown in FIG. 1 was used as a silicon manufacturing apparatus for realizing the steps shown in the flowchart of FIG. The basic configuration of the silicon recycling apparatus shown in FIG. 1 is the same as that of a general discharge plasma sintering apparatus. However, in the present embodiment, a point where a pulse current flows through the graphite mold 11 even after the starting raw material is sintered, and a runner (described later) through which molten silicon flows is formed in the graphite mold 11. This is very different from general spark plasma sintering equipment. However, the runner is not shown in FIG.

  First, the graphite mold 11 is filled with silicon powder 12 as a starting raw material (step S01 in FIG. 4). The graphite mold 11 has an inner diameter of 20 mm, an outer diameter of 50 mm, and a height of 40 mm.

  Next, the upper punch 13 is pushed into the graphite mold 11 and pressurized at 30 MPa, and pulsed power is supplied from the pulse power source 17 to raise the temperature of the graphite mold 11 to 1350 ° C. (step S02 in FIG. 4). Then, this state is held for 10 minutes (step S03 in FIG. 4). In step S02 of FIG. 4, pulse energization from the pulse power source 17 energizes the upper punch 13 by supplying ON-OFF DC pulse current via the pressure shaft 15 and pressurizes the lower punch 14. The lower part is energized by supplying an ON-OFF direct current pulse current through the shaft 16.

  By thus maintaining the pressure and pulse energization, the silicon powder 12 in the graphite mold 11 changes to a sintered body (step S04 in FIG. 4). During sintering, the inside of the vacuum chamber 18 is evacuated to a non-oxidizing atmosphere.

  Here, the temperature at the time of sintering in the present embodiment will be described. In the spark plasma sintering method shown in FIG. 5, the temperature during sintering is 1100 ° C., but the temperature during sintering in the present embodiment shown in FIG. 4 is as high as 1350 ° C. In the present embodiment, the sintering temperature is as high as 1350 ° C. in order to further reduce oxygen as an impurity.

That is, as described above, the surface of the silicon powder 12 that is a starting raw material filled in the graphite mold 11 is covered with an oxide film (SiO ₂ ). In this state of being covered with the oxide film, the oxide film serves as a heat insulating material, so that heat conduction from the graphite mold 11 to the silicon powder 12 becomes extremely poor. Therefore, in the state where the oxide film remains on the surface, there is a possibility that the sintering is not sufficiently performed. Since this oxide film is a substance containing a large amount of oxygen as an impurity, it is desirable to sinter after removing it. Therefore, in the sintering process of the present embodiment, the oxygen contained in the SiO ₂ film is removed by a reduction reaction by maintaining the temperature of the graphite mold 11 at 1350 ° C. for 10 minutes. This reduction reaction is expressed by a reaction formula of SiO ₂ + Si → 2SiO. Therefore, it can be estimated that oxygen is removed in a gaseous state of SiO.

  Here, the holding time of the graphite mold 11 at 1350 ° C. varies depending on the filling amount of the silicon powder 12 and the oxygen content of the silicon powder 12 before sintering. Therefore, it is necessary to obtain an appropriate time by experiments or the like. is there.

  As described above, in the flowchart of the discharge plasma sintering method shown in FIG. 5, when the silicon powder is sintered, silicon that has become a sintered body is taken out of the graphite mold. After the silicon powder became a sintered body, the pulse current was kept flowing while being pressurized at 30 MPa to raise the temperature of the graphite mold 11 to 1450 ° C. Further, in this embodiment, this state is maintained for 5 minutes (step S11 in FIG. 4). By this treatment, the sintered body of the silicon material inside the graphite mold 11 is changed to molten silicon (step S12 in FIG. 4). Even during melting, the inside of the vacuum chamber 18 is evacuated to a non-oxidizing atmosphere. In this case, the pulse current is supplied while being pressurized. However, depending on the conditions, the pulse current may be supplied without being pressurized and melted, and then the pressure may be applied.

As described above, in this embodiment, after removing the SiO ₂ film covering the surface of the silicon powder 12 to obtain a sintered body, the pulsed current is continuously supplied to raise the temperature of the graphite mold 11 to 1450 ° C. I am letting. In this way, the carbon component of silicon can now be removed by an oxidation reaction with oxygen remaining slightly in the graphite mold 11.

  As described above, with respect to silicon manufactured using the present embodiment, the impurities were measured by the combustion method. As a result, oxygen was 10 ppm and carbon was 120 ppm. Could be reduced.

  In the process of the present embodiment, when the graphite mold 11 is heated to 1450 ° C., the silicon powder 12 in the graphite mold 11 is heated to a temperature higher than 1410 ° C., which is the melting point of silicon. Therefore, as already described, silicon changes from a sintered state to a molten state inside the graphite mold 11 (step S12 in FIG. 4).

  In the present embodiment, a pressure of 30 MPa is applied to the silicon when the graphite mold 11 is heated from 1350 ° C. to 1450 ° C. When the silicon inside the graphite mold 11 exceeds the melting point and changes from a sintered body to a molten state with pressure applied to the silicon, the upper punch 13 is further pushed into the graphite mold 11 due to a decrease in the Young's modulus of silicon. When the upper punch 13 is further pushed into the graphite mold 11, the molten silicon inside the graphite mold 11 is pushed out, and the molten silicon oozes out from the gap between the upper punch 13 and the graphite mold 11 (step S13 in FIG. 4).

  In the present embodiment, as shown in FIGS. 6 (a) to 6 (c) and FIGS. 7 (a) to 7 (c), the molten silicon 21 moves from the gap between the graphite mold 11 and the upper punch 13. In order to prevent spraying and scattering well, a runner 19 through which the molten silicon 21 flows is provided on the inner surface and the end surface of the graphite mold 11. The molten silicon 21 that has flowed out of the graphite mold 11 through the runner 19 is collected in a collection container 20 installed outside the graphite mold 11 without leaking or splashing (step S14 in FIG. 4).

  When the recovery of the molten silicon 21 is completed, pressurization and pulse energization are stopped (step S05 in FIG. 4), and the upper punch 13 is moved upward.

  Next, a method for recovering molten silicon in the present embodiment will be described with reference to FIGS. 6 (a) to 6 (c) and FIGS. 7 (a) to 7 (c).

  FIGS. 6 (a) to 6 (c) and FIGS. 7 (a) to 7 (c) show the operation of the punch in the present embodiment. FIGS. 6 (a) to 6 (c) FIG. 7A to FIG. 7C are cross-sectional perspective views. Specifically, FIG. 6A and FIG. 7A show a state immediately before the upper punch 13 is inserted into the graphite mold 11. FIGS. 6B and 7B show a state in which the upper punch 13 is inserted into the graphite mold 11 and sintering is started. FIG. 6C and FIG. 7C show a state where the molten silicon 21 flows out through the runner 19. In particular, FIG. 7C shows a state in which the molten silicon 21 is pushed upward through the runner 19 provided on the inner surface of the graphite mold 11.

  As shown in FIGS. 6 (a) and 7 (a), the upper punch 13 disposed above the graphite mold 11 is lowered as shown in FIGS. 6 (b) and 7 (b). Silicon powder 12 (not shown) filled in the graphite mold 11 is compressed inside the graphite mold 11. In the present embodiment, simultaneously, a pulse current is supplied to the graphite mold 11. Thereby, at the same time as the temperature of the graphite mold 11 rises, the oxide film on the surface of the silicon powder 12 is removed, and sintering is started.

  Furthermore, by continuing to flow a pulse current and raising the temperature of the graphite mold 11 to 1450 ° C., which is 1410 ° C. or higher, which is the melting point of silicon, the silicon inside the graphite mold 11 changes from the sintered state to the molten state.

  By further lowering the upper punch 13, the molten silicon 21 passes through the runner 19 provided between the graphite mold 11 and the upper punch 13 as shown in FIG. Pushed up to the top.

  When the mold shape is circular like the graphite mold 11 in the present embodiment, the runner 19 is desirably arranged point-symmetrically with respect to the center of the mold. This arrangement is effective for uniformly dispersing the flow of the molten silicon 21. In the present embodiment, the runners 19 are arranged at three locations equally spaced by 120 ° with respect to the center of the circular graphite mold 11.

  The cross-sectional size of the runner 19 needs to be within a certain range. For example, when the cross-sectional area of the runner 19 is large and the volume of the runner 19 is too larger than the filling amount (volume) of the silicon powder 12, when the molten silicon 21 is extruded from the graphite mold 11, the upper punch 13 and the lower punch Even if it is pushed in until it comes into contact with the punch 14, most of the molten silicon 21 collects in the runner 19 and does not overflow from the graphite mold 11, and it is assumed that the molten silicon 21 cannot be efficiently recovered. . Further, when the cross-sectional area of the runner 19 is small and the volume of the runner 19 is too small with respect to the filling amount of the silicon powder 12, when the molten silicon 21 is extruded from the graphite mold 11, the narrow cross-sectional area is reduced. Therefore, it is assumed that the molten silicon 21 overflowing from the graphite mold 11 through the runner 19 has a strong momentum and is difficult to recover due to scattering to the surroundings.

  Therefore, in the present embodiment, the size of the cross section of the runner 19 in the graphite mold 11 is 2 mm in length and 2 mm in width.

  Since the material of the graphite mold 11 is graphite, the runner 19 in the present embodiment is formed by a slotter machine used for keyway processing. It is also possible to mold the graphite mold 11 having the shape of the runner 19 in advance using a mold.

  The molten silicon 21 can be stably recovered by arranging the recovery container 20 along the runner 19. Moreover, the silicon | silicone hardened | cured to the desired shape can be obtained by designing the internal shape of the collection container 20 suitably.

  In this embodiment, the inside of the vacuum chamber 18 is evacuated to form a non-oxidizing atmosphere. However, the inside of the chamber is filled with nitrogen gas, argon gas, hydrogen gas, or a mixed gas thereof to form a non-oxidizing atmosphere. May be.

  As described above, in the silicon manufacturing method of the present embodiment, in a non-oxidizing atmosphere, a pulse current is passed through a graphite mold and a punch is pressed, and the silicon powder filled in the graphite mold is heated and sintered. Further, a pulse current is applied to melt the sintered silicon powder inside the graphite mold, while a punch is pushed into the graphite mold, and the molten silicon is pushed out from the runner formed in the graphite mold to obtain a high-purity silicon material. obtain.

  In addition, the silicon recycling apparatus of the present embodiment includes a graphite mold, a punch, and a pulse power source for causing a pulse current to flow through the graphite mold. The graphite mold is filled with silicon powder in a non-oxidizing atmosphere. The silicon powder was heated and sintered by pushing the punch into the electrode and flowing the pulse current, and then the pulse current was further flown to push the punch into the graphite mold while melting the sintered silicon powder inside the graphite mold. The molten silicon is extruded from the runner formed in step 1 to obtain a high-purity silicon material.

  According to the embodiment described above, the silicon powder generated from the silicon wafer manufacturing process is sintered and melted in a non-oxidizing atmosphere by using a discharge plasma sintering method, thereby enabling high purity that can be reused. Silicon material can be manufactured. In particular, silicon sludge generated from a silicon wafer manufacturing process that has been disposed of as waste until now can be recycled into high-purity silicon that can be used to manufacture polysilicon, which is a raw material for solar cells and semiconductors. Thus, by recycling silicon powder that has been disposed of as waste as a polysilicon raw material, it is possible to contribute to the reduction of the manufacturing cost of the polysilicon raw material and the stable supply of the polysilicon raw material.

  In addition, even after the silicon powder inside the graphite mold (female mold) changes from the sintered state to the molten state, pressing the punch (male type) further extrudes the molten silicon from the graphite mold and the molten silicon flows. By forming the runner in a graphite mold, it becomes possible to efficiently take out the molten silicon accumulated in the graphite mold.

  The present invention can regenerate silicon powder generated from a silicon wafer manufacturing process into a high-purity silicon material in which the content of impurities that are a problem when manufacturing polysilicon as a raw material of a silicon wafer is reduced to the ppm order. It can be used to supply silicon materials to the fast growing solar cell industry.

DESCRIPTION OF SYMBOLS 1, 17 Pulse power source 2 Upper punch electrode 3 Lower punch electrode 4, 13 Upper punch 5, 14 Lower punch 6 Sintering die 8 Silicon powder 9, 18 Vacuum chamber 11 Graphite type 12 Silicon powder 15, 16 Press shaft 19 Runway 20 Recovery container 21 Molten silicon

Claims (11)

  A silicon manufacturing method comprising: sintering silicon powder in a container by a discharge plasma sintering method; and applying a current to the container to melt the silicon powder in the container to generate molten silicon. Method.   2. The silicon production according to claim 1, wherein the sintered silicon powder is melted while being pressurized in the container, and the molten silicon is allowed to flow outside the container through a runner formed in the container. Method.   The method for producing silicon according to claim 1, wherein a graphite mold is used as the container.   4. The silicon manufacturing method according to claim 1, wherein a pulse current is used as the current supplied to the container.   5. The method for producing silicon according to claim 1, wherein, in a non-oxidizing atmosphere, the silicon powder in the container is sintered and then melted to produce molten silicon.   A silicon recycling method for recycling silicon using a silicon powder generated from a silicon wafer manufacturing process and using the silicon manufacturing method according to claim 1. A container,
A punch for pressurizing the contents of the container;
A power source for passing current through the vessel;
A control device for controlling the operation of the punch and the operation of the power source;
The silicon powder in the container is pressurized by the punch under the control of the control device, and a current is passed from the power source to the container to sinter the silicon powder, and then the power source is used to sinter the container. A silicon manufacturing apparatus, wherein molten silicon is produced by flowing an electric current to the silicon powder to melt the sintered silicon powder.   The silicon manufacturing apparatus according to claim 7, wherein the molten silicon is allowed to flow to the outside of the container through a runner formed in the container.   The silicon manufacturing apparatus according to claim 7 or 8, wherein a graphite mold is used as the container.   10. The silicon manufacturing apparatus according to claim 7, wherein a pulse current is used as a current supplied from the power source to the container.   11. The silicon manufacturing apparatus according to claim 7, wherein the silicon powder in the container is sintered and then melted in a non-oxidizing atmosphere to produce the molten silicon.

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