JP4475524B2 - Granular silicon manufacturing method and manufacturing apparatus - Google Patents

Description

  In the present invention, a silicon melt heated and melted in a melting crucible is discharged from a nozzle provided at the bottom of the melting crucible, and granulated silicon melt droplets are dropped in a downcomer, and the silicon melt is dropped during the dropping. The present invention relates to a granular silicon manufacturing method and a manufacturing apparatus for manufacturing granular silicon by crystal growth by cooling molten droplets by heat radiation.

In recent years, development of new mass production technology of granular silicon used as a solar cell element capable of high-efficiency power generation is expected. A conventional apparatus for producing granular silicon, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2004-881), installs a melting crucible in a high-temperature heating furnace and descends to the lower part of the high-temperature heating furnace. Connecting the pipe vertically downward, communicating the space directly below the melting crucible in the high-temperature heating furnace to the downcomer, heating and melting the silicon raw material accommodated in the melting crucible to make a silicon melt, The silicon melt is discharged into the downcomer from the nozzle provided at the bottom of the melt crucible to drop the silicon melt droplet granulated in the downcomer, and the silicon melt droplet is dropped during the fall. There is one in which granular silicon is produced by growing crystals by cooling with heat radiation. In this method, during the production process of granular silicon, an extruded gas is introduced into the melting crucible so that the pressure in the melting crucible is higher than the pressure in the downcomer, so that the silicon melt in the molten crucible is at the bottom. It pushes out from the nozzle.
JP 2004-881 A

  Since the quality of the granular silicon produced by this method increases as the crystal grains become larger, the recent important research subject is to develop a mass production technique for enlarging the crystal grains.

  Therefore, in Patent Document 1, in order to manufacture granular silicon having large crystal grains, an after heater is provided in the downcomer, and the atmospheric gas in the downcomer is heated, so that a cooling temperature gradient near the freezing point of the silicon melt droplet is obtained. A method is adopted in which the nucleation rate inside the silicon melt droplet is suppressed by slowing down. However, since this method requires an after heater, there is a drawback in that the power consumption during the manufacturing process increases and the manufacturing cost of granular silicon increases.

  Further, in Patent Document 1, by filling the downcomer with an inert gas having a low thermal conductivity, the heat dissipation property of the silicon melt droplet falling in the downcomer is lowered, and the cooling rate by the heat dissipation of the silicon melt droplet is reduced. The method of slowing down is also adopted. In this case, the lower the atmospheric gas pressure (gas density) in the downcomer, the smaller the atmospheric gas heat transfer coefficient. Therefore, the atmospheric gas pressure in the downcomer is reduced to a pressure (negative pressure) lower than atmospheric pressure. For example, it is expected that the silicon crystal grains can be made sufficiently large by sufficiently slowing the cooling rate due to heat radiation of the silicon melt droplets falling in the downcomer.

  However, the above-described conventional manufacturing apparatus is configured to maintain the pressure of the atmospheric gas in the downcomer at atmospheric pressure or higher during the granular silicon manufacturing process. It is not assumed that the pressure is reduced to a lower pressure (negative pressure). Therefore, in order to produce large-grain granular silicon, the pressure of the atmospheric gas in the downcomer is reduced to a pressure lower than the atmospheric pressure (negative pressure), and the pressure in the melting crucible is reduced to the pressure in the downcomer (negative). Development of technology that adjusts higher than pressure) is expected.

  The present invention has been made in consideration of such circumstances, and therefore the object thereof is to optimize the pressure in the downcomer and the melting crucible to produce granular silicon having large crystal grains at low cost. The object is to provide a silicon manufacturing method and manufacturing apparatus.

In order to achieve the above object, the present invention provides a melting crucible in a high-temperature heating furnace, and a downcomer is connected vertically downward to the lower part of the high-temperature heating furnace so as to connect the melting crucible in the high-temperature heating furnace. The space immediately below is communicated with the downcomer, and the silicon raw material accommodated in the melting crucible is heated and melted to form a silicon melt, and the silicon melt is supplied from a nozzle provided at the bottom of the melting crucible. By discharging into the downcomer, the silicon melt droplet granulated in the downcomer is dropped, and the silicon melt droplet is cooled by heat dissipation during the fall to produce crystal silicon to produce granular silicon The atmospheric gas is introduced into the downcomer to adjust the pressure in the downcomer to a predetermined negative pressure, and the atmospheric gas is also introduced into the molten crucible to reduce the pressure in the molten crucible to the pressure in the downcomer. Remote adjusted to a predetermined pressure by a high pressure, it has a first feature in that the production of granular silicon extruding the molten silicon in the molten crucible from the nozzle by a pressure difference of the melting crucible and out, furthermore, A pressure vessel for storing the atmospheric gas supplied from the atmospheric gas supply source at the same pressure as the target pressure of the melting crucible, and a valve provided in a pipe communicating the pressure vessel and the melting crucible, In a state where the pressure in the melting crucible is reduced, the valve is opened to allow the pressure vessel and the melting crucible to communicate, thereby introducing a part of the atmospheric gas in the pressure vessel into the melting crucible and A second feature is that the pressure in the crucible is increased to the target pressure. In this way, the pressure difference between the inside and outside of the melting crucible is reduced by making the pressure in the downcomer pipe negative and reducing the heat dissipation of the silicon melt droplets falling in the downcomer pipe. Can be pushed out of the nozzle and dropped into the downcomer, and the cooling rate by the heat radiation of the silicon melt droplets falling through the downcomer can be effectively slowed down, producing large-grain granular silicon at low cost can do. In addition , a pressure vessel for storing the atmospheric gas supplied from the atmospheric gas supply source at the same pressure as the target pressure of the molten crucible, and a valve provided in a pipe for communicating the pressure vessel and the molten crucible are provided. Then, by opening the valve in a state where the inside of the melting crucible is decompressed and communicating the pressure vessel and the melting crucible, a part of the atmospheric gas in the pressure vessel is introduced into the melting crucible, since the pressure of the molten crucible was set to be increased to the target pressure, if a sufficiently large volume of the pressure vessel with respect to the space volume and the piping volume of the melt in the crucible, with a simple structure using the pressure vessel The pressure in the melting crucible can be stably maintained at the target pressure.

  Hereinafter, three Examples 1 to 3 embodying the best mode for carrying out the present invention will be described.

A first embodiment of the present invention will be described with reference to FIGS.
First, the configuration of the granular silicon manufacturing apparatus will be described.
A core tube 12 formed in a cylindrical shape with graphite or the like is provided in the core portion of the high-temperature heating furnace 11 in a vertical direction, and a heater such as a resistance heater or a high-frequency induction heating coil is provided around the core tube 12. 14 is provided. A cylindrical crucible-shaped melting crucible 13 is inserted into the core tube 12 from above, and the bottom of the melting crucible 13 is fixed in a state of being located near the center of the core tube 12. The molten crucible 13 is formed of high-purity quartz to prevent impurities from being mixed into the silicon melt 17 melted therein, and the molten crucible 13 and the inner peripheral surface (core inner peripheral wall) of the core tube 12 and A cylindrical gap is formed between the two. A nozzle 15 is provided at the bottom of the melting crucible 13 downward to continuously discharge the silicon melt 17 in a linear shape. For example, when producing granular silicon having a diameter of about 1 mm, the diameter of the nozzle 15 is preferably set to 0.3 to 0.5 mm.

  A downcomer 16 is connected to the lower part of the high-temperature heating furnace 11 vertically downward. The downcomer 16 is filled with an inert gas such as argon or helium as an atmospheric gas. In this case, since the heat transfer coefficients are different between argon and helium, there is a difference in the cooling rate due to heat radiation of the falling silicon melt droplet. Therefore, the cooling rate of the silicon melt droplets can be adjusted by properly using argon and helium as the atmospheric gas in the downcomer 16 or adjusting the mixing ratio of the two.

  Note that a lower end of the downcomer 16 is provided with a recovery container 18 (see FIG. 2) for recovering falling granular silicon, and the same atmospheric gas as the downcomer 16 is also filled in the recovery container 18. . Cooling oil (silicon oil, quenching oil, etc.) for cooling the granular silicon may be stored in the collection container 18, but the cooling oil need not be stored.

Next, the configuration of the atmospheric gas introduction / discharge system will be described with reference to FIG.
A main exhaust port 21 for evacuating the inside of the core tube 12 and the downcomer tube 16 of the high temperature heating furnace 11 is provided in the lower part of the high temperature heating furnace 11 (or the upper part of the downcomer pipe 16). A vacuum pump 24 is connected via a main exhaust valve 23 to the main exhaust pipe 22 connected to. Further, a gas introduction port 25 for introducing atmospheric gas is provided in the lower part (or downcomer 16) of the high temperature heating furnace 11, and a gas discharge port 26 is provided in the upper part of the high temperature heating furnace 11.

  An atmosphere gas is introduced into the high-temperature heating furnace 11 and the downcomer pipe 16 from a gas cylinder 27 serving as an atmosphere gas supply source through a path of regulator R 1 → gas introduction flow rate adjustment valve 29 → electromagnetic valve V 6 → gas introduction port 25. In this case, an inert gas such as argon or helium is used as the atmospheric gas in order to prevent the hot silicon melt droplets discharged from the nozzle 15 at the bottom of the melting crucible 13 from reacting with the atmospheric gas.

  In addition, an electromagnetic valve V5 is provided in parallel in the series circuit of the gas introduction flow rate adjustment valve 29 and the electromagnetic valve V6, and in the vicinity of the gas introduction port 25, a pressure for measuring the pressure of the atmospheric gas in the downcomer 16 is measured. A total of 32 is provided. On the other hand, the gas discharge port 26 communicates with the outside air (atmosphere) through the electromagnetic valve V7.

  In the first embodiment, a part of the atmospheric gas discharged from the gas cylinder 27 is introduced into the melting crucible 13 through the path of regulator R1, regulator R2, electromagnetic valve V1, and electromagnetic valve V2.

  The inside of the melting crucible 13 is connected to a pressure vessel 39 via an electromagnetic valve V3, and the pressure vessel 39 is provided with a pressure gauge 40 for measuring the internal pressure. Further, the two electromagnetic valves V1 and V2 are connected to the gas inlet 25 side via the electromagnetic valve V4. When the inside of the downcomer 16 is depressurized and evacuated by the vacuum pump 24, the electromagnetic valves V1, V5, When V6 and V7 are closed and the other electromagnetic valves V2, V3 and V4 and the main exhaust valve 23 are opened, the inside of the melting crucible 13 and the inside of the pressure vessel 39 can be simultaneously decompressed and evacuated by the vacuum pump 24. .

  Next, a method of manufacturing granular silicon using the granular silicon manufacturing apparatus having the above configuration will be described. First, as a preparatory work, the downcomer pipe is operated by operating the vacuum pump 24 with the electromagnetic valves V1, V5, V6, V7 closed and the other electromagnetic valves V2, V3, V4 and the main exhaust valve 23 opened. At the same time that the inside of 16 is evacuated, the inside of the melting crucible 13 containing the silicon raw material and the inside of the pressure vessel 39 are evacuated. When these are sufficiently evacuated, the main exhaust valve 23 is closed and evacuation by the vacuum pump 24 is stopped, and then the electromagnetic valves V1 and V5 are opened (the electromagnetic valve V6 may also be opened). ), The atmospheric gas discharged from the gas cylinder 27 is filled into the downcomer 16, and at the same time, the atmospheric gas is filled into the melting crucible 13 and the pressure vessel 39. Thereby, the inside of the downcomer 16, the melting crucible 13, and the pressure vessel 39 are filled with the atmospheric gas corresponding to the atmospheric pressure.

  Thereafter, the electromagnetic valves V1, V5, V6, V7 are closed, and the vacuum pump 24 is operated in a state where the other electromagnetic valves V2, V3, V4 and the main exhaust valve 23 are opened. At the same time, the inside of the melting crucible 13 and the inside of the pressure vessel 39 are decompressed. As a result, the pressure gauge 40 detects that the pressure in the pressure vessel 39 has been reduced to the target negative pressure P1 (= target negative pressure P3 in the downcomer 16 when discharging the silicon melt + differential pressure ΔP ± correction value α). At that time, the electromagnetic valve V3 on the pressure vessel 39 side is closed to maintain the pressure in the pressure vessel 39 at the target negative pressure P1. Thereafter, the vacuum pump 24 is continuously operated to depressurize the downcomer 16. In this case, the target negative pressure P3 in the downcomer 16 when discharging the silicon melt is set to a pressure considerably lower than the atmospheric pressure, and the differential pressure ΔP pushes the silicon melt 17 in the melting crucible 13 from the nozzle 15. The correction pressure α is set according to the internal volume of the pressure vessel 39, the internal volume of the molten crucible 13, and the internal volume of the pipe line.

  Thereafter, when the pressure gauge 32 detects that the pressure in the downcomer 16 has been reduced to the target negative pressure P3 when discharging the silicon melt, the electromagnetic valves V2, V4 and the main exhaust valve 23 are closed, The pressure reduction in the downcomer 16 by the vacuum pump 2 is finished, and the pressure in the downcomer 16 is maintained at the target negative pressure P3 when discharging the silicon melt (this function is used as the downcomer pressure adjusting means in the claims). Equivalent to).

  Thereafter, the heater 14 of the high temperature heating furnace 11 is heated to heat and melt the silicon raw material in the melting crucible 13 to make a silicon melt 17. As a result, when the temperature of the silicon melt 17 in the melting crucible 13 becomes sufficiently higher than the melting point, the electromagnetic valve V3 on the pressure vessel 39 side is opened and the atmospheric gas in the pressure vessel 39 is introduced into the melting crucible 13. Then, the pressure in the melting crucible 13 is increased to the target negative pressure P1 (= target negative pressure P3 in the descending pipe 16 when discharging the silicon melt + differential pressure ΔP), and the pressure in the melting crucible 13 is lowered. It is made higher than the negative pressure P3 by a predetermined differential pressure ΔP (this function corresponds to the melting crucible pressure adjusting means in the claims). Accordingly, the silicon melt 17 in the melting crucible 13 is discharged so as to continuously flow linearly from the nozzle 15 at the bottom of the melting crucible 13 by the pressure difference ΔP inside and outside the melting crucible 13.

  In this way, the linear silicon melt 17 discharged from the nozzle 15 freely falls in the downcomer 16, but at that time, the diameter is reduced by the gravitational acceleration, and finally the silicon melt 17. The silicon melt 17 is crushed and granulated by the fluctuation of the silicon melt 17 caused by the surface tension and the gravitational acceleration, and the silicon melt droplets of small diameter are freely dropped in the downcomer 16. The silicon melt droplets dissipate heat while dropping, so that silicon crystals grow to form granular silicon, which is collected in the collection container 18. During the manufacturing process of the granular silicon, all the electromagnetic valves V1 to V7 and the main exhaust valve 23 are kept closed, and the pressure in the melting crucible 13 is set to the target negative pressure P1 (= the downcomer when discharging the silicon melt). 16 is maintained at the target negative pressure P3 + differential pressure ΔP), and the pressure in the downcomer 16 is maintained at the target negative pressure P3 when the silicon melt is discharged.

  According to the first embodiment described above, the atmospheric gas is introduced into the downcomer 16 to adjust the pressure in the downcomer 16 to the predetermined negative pressure P3, and the atmospheric gas is also introduced into the melting crucible 13. Then, the pressure in the melting crucible 13 is adjusted to a negative pressure P1 higher than the negative pressure P3 in the downcomer pipe 16 by a predetermined pressure ΔP, and the silicon melt in the melting crucible 13 is adjusted by the pressure difference ΔP inside and outside the melting crucible 13. Since the granular silicon is produced by extruding the nozzle 17 from the nozzle 15, the pressure in the downcomer pipe 16 is set to a negative pressure, and the heat dissipation of the silicon melt droplets falling in the downcomer pipe 16 is reduced, while the melting crucible is The silicon melt 17 heated and melted in 13 can be pushed out of the nozzle 15 by the pressure difference between the inside and outside of the melting crucible 13 and dropped into the downcomer 16 to dissipate the silicon melt droplet falling in the downcomer 16. Accordingly, the cooling rate can be effectively reduced, and granular silicon with large crystal grains can be produced at low cost.

  Moreover, in the first embodiment, the pressure vessel 39 that stores the atmospheric gas supplied from the gas cylinder 27 at the same pressure as the target negative pressure P1 of the melting crucible 13 and the piping that connects the pressure vessel 39 and the melting crucible 13 are connected. And the electromagnetic valve V3 is opened in a state where the inside of the melting crucible 13 is depressurized to allow the pressure vessel 39 and the melting crucible 13 to communicate with each other. Is introduced into the melting crucible 13 and the pressure in the melting crucible 13 is increased to the target negative pressure P1. If the volume is sufficiently large, the pressure in the melting crucible 13 can be stably maintained at the target negative pressure P1 with a simple configuration using the pressure vessel 39.

  In the first embodiment, the gas discharge port 26 at the top of the high-temperature heating furnace 11 is communicated with the outside air (atmosphere) via the electromagnetic valve V7. However, in the second embodiment of the present invention shown in FIG. 26 is connected to the vacuum pump 42 through the path of the electromagnetic valve V7 → the gas discharge flow rate adjustment valve 41 → the electromagnetic valve V8 so that the atmospheric gas discharge flow rate from the gas discharge port 26 can be adjusted by the gas discharge flow rate adjustment valve 41. .

  Furthermore, in the second embodiment, the pressure in the pressure vessel 39 can be adjusted by the two flow rate adjusting valves 43 and 44 via the electromagnetic valve V9. In this case, one flow rate adjustment valve 43 is connected to the gas cylinder 27 via the regulator R 1, and the other flow rate adjustment valve 44 is connected to the vacuum pump 42.

  For example, when the pressure in the pressure vessel 39 falls below the target pressure during the manufacturing process of granular silicon, the flow rate adjustment valve 44 on the vacuum pump 42 side is closed and the electromagnetic valve V9 is opened, and the atmospheric gas is discharged from the gas cylinder 27. The flow rate is adjusted by the flow rate adjusting valve 43 to flow into the pressure vessel 39. Thus, when the pressure gauge 40 detects that the pressure in the pressure vessel 39 has increased to the target pressure, the electromagnetic valve V9 is closed. When the pressure in the pressure vessel 39 exceeds the target pressure and becomes too high, the flow rate adjustment valve 43 on the gas cylinder 27 side is closed and the electromagnetic valve V9 is opened, and the atmosphere in the pressure vessel 39 is opened by the vacuum pump 42. Gas is sucked while the flow rate is adjusted by the flow rate adjusting valve 44. Thereby, when the pressure gauge 40 detects that the pressure in the pressure vessel 39 has decreased to the target pressure P1, the electromagnetic valve V9 is closed and the vacuum pump 42 is stopped. Other configurations are the same as those of the first embodiment.

  In the second embodiment described above, when the pressure in the pressure vessel 39 (pressure in the melting crucible 13) deviates from the target pressure during the production process of granular silicon, the pressure in the pressure vessel 39 (melting crucible 13). The internal pressure) can be adjusted by the two flow rate adjusting valves 43 and 44 via the electromagnetic valve V9.

In the third embodiment as a reference example related to the present invention shown in FIG. 3, the pressure vessel 39 and the electromagnetic valve V9 used in the second embodiment (FIG. 3) are omitted, and the pressure in the melting crucible 13 is measured by the pressure gauge 40. It is set as the structure which detects. Other configurations are the same as those of the second embodiment (FIG. 3).

  In the third embodiment, the inside of the downcomer 16, the melting crucible 13, and the pressure vessel 39 are filled with atmospheric gas corresponding to atmospheric pressure in the same manner as in the first embodiment, and then the electromagnetic valves V 1, V 3, V 5 are filled. By operating the vacuum pump 24 with the electromagnetic valves V2 and V4 and the main exhaust valve 23 opened while the V6 and V7 are closed, the inside of the downcomer 16 is decompressed and at the same time the interior of the melting crucible 13 is decompressed. As a result, when the pressure gauge 32 detects that the pressure in the downcomer 16 has been reduced to the target negative pressure P3 when discharging the silicon melt, the electromagnetic valves V2, V4 and the main exhaust valve 23 are closed. Then, the pressure reduction in the downcomer 16 and the melting crucible 13 by the vacuum pump 2 is finished, and the pressure in the downcomer 16 and the melting crucible 13 is maintained at the target negative pressure P3 when discharging the silicon melt.

  Thereafter, the heater 14 of the high temperature heating furnace 11 is heated to heat and melt the silicon raw material in the melting crucible 13 to make a silicon melt 17. Thereby, when the temperature of the silicon melt 17 in the melting crucible 13 becomes sufficiently higher than the melting point, the electromagnetic valve V3 is opened, and the atmospheric gas supplied from the gas cylinder 27 is melted while adjusting the flow rate by the flow rate adjusting valve 43. The pressure in the melting crucible 13 is introduced into the crucible 13 and the pressure in the melting crucible 13 is increased so that the pressure in the melting crucible 13 is the target negative pressure P1 (= target negative pressure P3 in the downcomer 16 when discharging the silicon melt + differential pressure ΔP). When the pressure gauge 40 detects that the pressure has risen, the electromagnetic valve V3 is closed and the melting crucible 13 is sealed. Thereby, the silicon melt 17 in the melting crucible 13 is discharged so as to continuously flow linearly from the nozzle 15 at the bottom of the melting crucible 13 by the pressure difference ΔP inside and outside the melting crucible 13 to produce granular silicon. .

The third embodiment described above has an advantage that the manufacturing apparatus can be downsized because the large pressure vessel 39 is not required.
In each of the first to third embodiments, the gas discharge port 26 and the valves connected thereto (such as the electromagnetic valve V7) may be omitted.

It is a longitudinal cross-sectional view which shows the high temperature heating furnace and downcomer upper part of Example 1 of this invention. It is a figure explaining the system configuration | structure of the whole granular silicon manufacture of Example 1 of this invention. It is a figure explaining the system configuration | structure of the whole granular silicon manufacture of Example 2 of this invention. It is a figure explaining the system configuration | structure of the whole granular silicon manufacture of Example 3 as a reference example relevant to this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... High temperature heating furnace, 12 ... Core tube, 13 ... Molten crucible, 14 ... Heater, 15 ... Nozzle, 16 ... Downcomer, 17 ... Silicon melt, 21 ... Main exhaust port, 23 ... Main exhaust valve, 24 ... Vacuum Pump, 25 ... Gas inlet, 26 ... Gas outlet, 27 ... Gas cylinder (atmosphere gas supply source), 29 ... Gas introduction flow rate adjustment valve, 32 ... Pressure gauge, 33 ... Check valve, 39 ... Pressure vessel, 40 ... Pressure gauge, 41 ... Gas discharge flow rate adjustment valve, 42 ... Vacuum pump, 43, 44 ... Flow rate adjustment valve, V1 to V9 ... Solenoid valve, R1, R2 ... Regulator

Claims (1)

A melting crucible is installed in the high temperature heating furnace, a downcomer pipe is connected vertically downward to the lower part of the high temperature heating furnace, and a space directly below the melting crucible in the high temperature heating furnace is communicated with the downcomer pipe, A silicon raw material contained in the melting crucible is heated and melted to form a silicon melt, and the silicon melt is discharged into the downcomer pipe from a nozzle provided at the bottom of the molten crucible. In the granular silicon production apparatus for producing granular silicon by dropping the silicon melt droplet granulated in step, and crystal growth by cooling the silicon melt droplet by heat radiation during the fall,
Downcomer pressure adjusting means for introducing atmospheric gas into the downcomer and adjusting the pressure in the downcomer to a predetermined negative pressure;
A melting crucible pressure adjusting means for introducing atmospheric gas into the melting crucible and adjusting the pressure in the melting crucible to a pressure higher than the pressure in the downcomer by a predetermined pressure (hereinafter referred to as “target pressure”) ;
The molten crucible pressure adjusting means is provided in a pressure vessel for storing the atmospheric gas supplied from an atmospheric gas supply source at the same pressure as the target pressure of the molten crucible, and in a pipe that communicates the pressure vessel and the molten crucible. And opening the valve in a state where the inside of the melting crucible is decompressed to allow the pressure vessel and the melting crucible to communicate with each other, so that a part of the atmospheric gas in the pressure vessel is allowed to pass through the melting crucible. An apparatus for producing granular silicon, which is introduced into the molten crucible and raises the pressure in the molten crucible to the target pressure .

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