JP5168657B2 - Granular silicon manufacturing method and apparatus - Google Patents

Description

  The present invention relates to a granular silicon manufacturing method and apparatus, and more particularly to a granular silicon manufacturing method and apparatus capable of manufacturing granular silicon which is a substrate material for a polycrystalline silicon solar cell that performs photoelectric conversion.

  As a conventional method for producing granular silicon, a lump, granule, or microparticulate silicon material charged in a crucible is melted by high-frequency induction heating, and the molten silicon is dropped as a droplet (granular melt) from the crucible. A method is known in which molten silicon is spheroidized by surface tension (for example, Patent Document 1). At the start of operation of Patent Document 1, the silicon material immediately before being put into the crucible was preheated, and after being put into the crucible, it was melted by high frequency induction heating.

JP 2006-137622 A

By the way, the silicon material made from silicon single crystal or the like is made of high purity silicon. High-purity silicon has a high resistivity at room temperature (solid), and almost no induced current flows. Therefore, if the remaining silicon material discharged from the wafer processing process is used and the method described in Patent Document 1 is used, the silicon material is heated by resistance with a heater or the like to the vicinity of the melting point where the induced current flows during preheating. There was a need to do.
A large amount of powdered silicon is discharged from the slicing process and grinding process. Of the recoverable wafer residue, cutting powder has a large surface area and is highly contaminated by impurities. Therefore, it is difficult to reuse as a single crystal raw material for device wafers. Based on this, in recent years, methods for effectively using powdered silicon as a silicon material for solar cells have been studied.

Therefore, as a result of earnest research, the inventor adopted a crucible having a constricted shape as a crucible, and silicon that is melted indirectly by radiant heat of high-frequency induction heating in the lower opening of the crucible containing powdered silicon during initial melting. I came up with the idea of blocking with a block.
That is, at the start of production, the conductive cylinder provided around the lower opening is subjected to high-frequency induction heating, and the radiant heat melts the silicon block closing the lower opening of the crucible and part of the powdered silicon. Thereafter, heating with radiant heat is continued, or molten silicon is directly subjected to high frequency induction heating. Thereby, the powder silicon which reached the inside of the lower opening is melted sequentially. As a result, even if a silicon material made of high-purity silicon that hardly induces an induced current at room temperature is used, a preheating device is unnecessary and it is possible to produce granular silicon continuously from the start of production. As a result, the present invention was completed.

  In addition, since the crucible with a constricted shape is adopted, the crucible can be reduced in size and only the silicon material stored in the lower opening of the crucible is melted, so that the power consumed during high frequency induction heating can be reduced. We also found out that it was possible to complete this invention.

  This invention can reduce the power consumption during crucible downsizing and high-frequency induction heating, and even when high-purity silicon made of powder silicon is used, without using a preheating device, It is an object of the present invention to provide a granular silicon production method and apparatus capable of continuously producing granular silicon from the above.

The invention described in claim 1 is a crucible having a constricted shape in which powder silicon is introduced from an upper opening and molten silicon after melting of the powder silicon is continuously dropped from a lower opening, and the lower opening A high-frequency induction coil arranged around the outside of the unit, and provided between the high-frequency induction coil and the lower opening so as to be removable, heated by the activation of the high-frequency induction coil, and the radiant heat accommodates the powder silicon A silicon block that closes the lower opening of the crucible having a constricted shape, a conductive cylinder for auxiliary heating that melts part of the powdered silicon, the conductive cylinder, the high-frequency induction coil, and the lower opening It is the granular silicon manufacturing apparatus provided with the insertion / extraction means to insert / extract between .

According to the first aspect of the present invention, at the start of manufacture, the conductive cylinder is induction-heated by induction by activation of the induction coil, and the silicon block in the lower opening and a part of the powder silicon are melted by the radiant heat. After that, continue heating with this radiant heat, or use a pull-out means to pull out the conductive cylinder from between the high-frequency induction coil and the lower opening, and directly add the molten silicon whose electrical resistivity has decreased by heating, High frequency induction heating. Therefore, even when powder silicon made of high-purity silicon is used as the silicon material, granular silicon can be continuously produced from the start of production without using a preheating device that has been an essential facility in the past. In addition, since the crucible having a constricted shape is adopted, the crucible can be reduced in size. Furthermore, since the crucible heating range by the high frequency induction coil is the lower opening of the constricted shape, the heating volume of the crucible is small. Therefore, the electric power used at the time of high frequency induction heating can be reduced.

As “powder silicon”, cutting powder discharged from the slicing process or grinding process of the wafer processing process can be employed. The cutting powder has a larger surface area than the lump-shaped or granule-shaped wafer residue and is made of high-purity silicon, but its surface layer portion is highly contaminated by impurities.
As silicon, single crystal silicon or polycrystalline silicon can be employed.
As a material for the crucible, quartz, boron nitride, silicon carbide, or the like can be used.
The shape of the crucible is arbitrary as long as the lower opening is smaller than the upper opening in a cylindrical shape (cylindrical shape, rectangular tube shape, etc.).
The “bottom shape” is a shape in which the opening area gradually decreases downward. The crucible may have a constricted shape over the entire length of the crucible, or only the lower portion thereof may have a constricted shape.
The shape of the lower opening of the crucible may be, for example, a funnel shape in which the diameter is gradually reduced downward. Alternatively, it may be a cylindrical shape having a uniform opening area over the entire length of the lower opening. Or the shape by which the said cylinder which the opening area was equal over the full length was connected with the opening of the lower end of the said funnel part may be sufficient.

As the silicon block, for example, a block made of single crystal silicon, a block made of polycrystalline silicon, or a solidified crucible residue of this patent method can be adopted.
As the conductive material that is a material of the conductive cylinder, for example, a metal having a melting point of 2000 ° C. or higher, such as graphite or tungsten, can be used.
For high-frequency induction heating of the conductive cylinder, a high-frequency induction coil is used, and heating by the induction current can be employed.
The power supply for the high-frequency induction coil, for example 20～500KHz, is employed as the 20 to 200 k W.

  The heating temperature of the conductive cylinder is 600 to 1500 ° C. at which the silicon block can be melted by the radiant heat of the conductive cylinder. Below 600 ° C., the radiant heat is low and the time until the induced current starts to flow through the silicon block becomes long. Moreover, if it exceeds 1500 degreeC, the heat resistance of a crucible material will run short and deterioration will become intense. A preferable heating temperature of the conductive cylinder is 800 to 1000 ° C. Within this range, the problem of shortening the crucible life due to excessive radiant heat can be mitigated by inducing an induced current to flow into the silicon block in a short time and reaching a molten state.

The molten silicon in the lower opening may be continuously heated by the radiant heat of the conductive cylinder. Alternatively, the conductive cylinder may be removed and the molten silicon in the lower opening may be directly subjected to high frequency induction heating. This is because even if the raw material is high-purity silicon, since the silicon is heated to a temperature exceeding the melting point, the electrical resistivity of silicon is low and the induced current flows sufficiently.
When molten silicon is dropped from the lower opening of the crucible, the crucible may be vibrated by a vibrator so that the particle diameters of the granular molten silicon are made uniform.
As the insertion / extraction means, for example, various actuators that move the operation arm can be employed.

The invention according to claim 2 is the granular silicon manufacturing apparatus according to claim 1, further comprising a stirring nozzle for blowing a reducing gas onto the molten silicon while stirring the powdered silicon in the crucible .

According to the second aspect of the present invention, the powdered silicon adhering to the inner peripheral surface of the crucible in a suspended state is scraped off by stirring with the stirring nozzle. In the stirring, by using the vibrator provided on the upper part of the nozzle, the suspended state of the powder silicon can be easily eliminated. Moreover, a reducing gas is sprayed from the stirring nozzle toward the surface of the molten silicon. Thereby, the oxide on the surface of the powder silicon can be reduced by the reducing action of the gas.

  The oxygen concentration of the granular silicon produced | generated by this reducing gas reduces, and the conversion efficiency of a solar cell increases.

According to a third aspect of the present invention, the cooling inclined plate is provided immediately below the lower opening of the crucible, in which the granular silicon immediately after dripping and solidifying from the lower opening is cooled while rolling on the inclined surface. It is the granular silicon manufacturing apparatus of Claim 1 or Claim 2.

According to the third aspect of the present invention, the granular silicon dropped from the lower opening and spheroidized by the surface tension is cooled while rolling on the slope of the cooling inclined plate. Thereby, the deformation | transformation by the impact at the time of the granular silicon before fully solidifying colliding with the bottom plate of a collection container can be prevented, for example. In addition, the impurities adhering to the surface of the recovery container and the material of the recovery container itself are not taken in, and the risk of impurities being mixed into the granular silicon can be reduced.
As the cooling inclined plate, for example, the inclined surface may be flat or the inclined surface may be curved.

The invention according to claim 4 is the granular silicon manufacturing apparatus according to any one of claims 1 to 3 , wherein the opening diameter of the lower opening of the crucible is 5 to 20 mm.

  When the opening diameter (inner diameter) of the lower opening of the crucible is less than 5 mm, solidification of the molten silicon in the lower opening tends to occur and there is a risk of clogging. Moreover, if it exceeds 20 mm, the dripping amount of a molten silicon will increase, the molten silicon under a crucible will be lose | eliminated, and powdered silicon will not fuse | melt. Or powder silicon will leak from an opening. The preferable opening diameter of the lower opening is 5 to 10 mm. By setting this range, the power control of the high-frequency power source and the control range of the conductive cylinder for auxiliary heating in the lower part are reduced, and a more preferable effect that a stable molten silicon dropping amount can be obtained.

According to a fifth aspect of the present invention, there is provided a lid-stopping process in which the lower opening of the crucible with the constricted shape containing the powdered silicon is closed with a silicon block, and the outer opening of the lower opening is disposed after the lid-stopping process. A conductive cylinder for auxiliary heating made of a conductive material is induction-heated at high frequency, and the radiant heat melts the silicon block and a part of the powder silicon in the lower opening, and the molten silicon is continuously supplied from the lower opening. An initial melting step in which the molten silicon is dropped, and after the initial melting step, the molten silicon in the lower opening is continuously heated by radiant heat of the conductive cylinder, or the molten silicon in the lower opening is removed by removing the conductive cylinder. High-frequency induction heating, the powdered silicon that has reached the lower opening with continuous dripping of the molten silicon from the lower opening, sequentially, the heat of the molten silicon A granular silicon manufacturing method and a melting step of further melting.

According to the fifth aspect of the present invention, at the start of manufacture, the lower opening of the crucible is closed with the silicon block (covering step). Thereafter, the conductive cylinder arranged around the lower opening is subjected to high frequency induction heating, and the radiant heat melts the silicon block and part of the powdered silicon in the lower opening. Thereby, from the start of manufacture, molten silicon is continuously dripped from the lower opening, and granular silicon is manufactured by solidifying after spheroidization by surface tension (initial melting step). Thereafter, the molten silicon in the lower opening is continuously heated by radiant heat, or the conductive cylinder is removed, and the molten silicon is directly subjected to high frequency induction heating. As a result, the silicon powder that has fallen to the lower opening due to continuous dripping of the molten silicon is sequentially melted by the heat of the molten silicon. As a result, the production of granular silicon by dripping molten silicon is continued (melting step).

  Thus, at the start of manufacture, the conductive cylinder is induction-heated by induction by starting the high-frequency induction coil, and the silicon block in the lower opening and part of the powder silicon are melted by the radiant heat. After that, heating by radiant heat is continued, or the conductive cylinder is extracted from between the high-frequency induction coil and the lower opening by the insertion / extraction means, and the molten silicon whose electrical resistivity is reduced by heating is directly applied to the high-frequency induction heating. To do. Therefore, even if powder silicon made of high-purity silicon is adopted as the silicon material, granular silicon can be continuously produced from the start of production without using a preheating device. Furthermore, since the crucible having a constricted shape is adopted, the crucible can be downsized. Moreover, since the heating range of the crucible by the high-frequency induction coil is the lower opening of the constricted shape, the heating volume of the crucible is reduced. As a result, the power used during high frequency induction heating can be reduced.

According to the first and fifth aspects of the invention, at the start of manufacture, the conductive cylinder is induction-heated by induction by activation of the induction coil, and the radiant heat causes the silicon block in the lower opening and part of the powder silicon to Melt. After that, heating by radiant heat is continued, or the conductive cylinder is extracted from between the high-frequency induction coil and the lower opening by the insertion / extraction means, and the molten silicon whose electrical resistivity is reduced by heating is directly applied to the high-frequency induction heating. To do. Therefore, even when powder silicon made of high-purity silicon is adopted as the silicon material, granular silicon can be continuously produced from the start of production without using a preheating device. Furthermore, since the crucible having a constricted shape is adopted, the crucible can be downsized. Moreover, since the heating range of the crucible by the high-frequency induction coil is the lower opening of the constricted shape, the heating volume of the crucible is reduced. As a result, the power used during high frequency induction heating can be reduced.

In particular, according to the second aspect of the invention, the powder silicon adhering to the inner peripheral surface of the crucible in a suspended state is scraped off while stirring the powder silicon by the stirring nozzle. Moreover, a reducing gas is sprayed from the stirring nozzle toward the surface of the molten silicon. Thereby, oxidation of the liquid surface of molten silicon can be prevented by the reducing action of the gas.

According to the third aspect of the present invention, the granular silicon dropped from the lower opening and spheroidized by the surface tension is cooled while rolling on the slope of the cooling inclined plate. This prevents, for example, deformation caused by impact when the granular silicon before being completely hardened collides with the bottom plate of the recovery container, and impurities are not absorbed into the surface of the silicon grains due to the impact of the collision. The risk of contamination can be reduced.

According to the invention described in claim 4 , since the opening diameter of the lower opening of the crucible is set to 5 to 20 mm, stable melting of the silicon powder can be continued.

  Hereinafter, the granular silicon manufacturing method and apparatus according to Embodiment 1 of the present invention will be described in detail.

  In FIG. 1, reference numeral 10 denotes a granular silicon production apparatus according to Embodiment 1 of the present invention. In this granular silicon production apparatus 10, powder silicon 12 is introduced from an upper opening 11a, and powder silicon 12 is introduced from a lower opening 11b. Between the crucible 11 having a constricted shape in which molten silicon 13 in which molten silicon is melted is continuously dropped, the high frequency induction coil 14 arranged around the lower opening 11b, and the high frequency induction coil 14 and the lower opening 11b. A conductive cylinder 16 for auxiliary heating that is heated by activation of the high-frequency induction coil 14 and melts part of the silicon block 15 and the powdered silicon 12 in the lower opening by the radiation heat, and the conductive cylinder 16. Is provided between the high-frequency induction coil 14 and the lower opening portion 11b.

Hereinafter, these components will be described in detail.
The crucible 11 is a quartz container having a constricted shape as a whole. In FIG. 1, the lower inclination angle (25 °) is larger than the upper inclination angle (5 °) of the crucible 11. The inner diameter (opening diameter) of the upper opening 11a of the crucible 11 is 200 mm, and the lower end inner diameter of the lower opening 11b is 6 mm.
The lower opening 11b referred to here is a substantially lower half of the lower portion of the crucible 11, and is communicated with a funnel portion having a diameter gradually reduced downward and an opening at the lower end of the funnel portion. A portion including an equal cylindrical portion.

The powder silicon 12 and the silicon block 15 are made of silicon having a purity of 99.99%. The average particle diameter of the powder silicon 12 is 10 μm.
In the inner space of the crucible 11, an agitation nozzle 18 that blows the reducing gas G onto the liquid surface of the molten silicon 13 from the blowout port 18 a formed at the lower end while agitating the powder silicon 12 is accommodated. The stirring nozzle 18 is a thin tube that is long in the vertical direction, and is provided with a 60 Hz electromagnetic vibrator (not shown). As the reducing gas G, argon gas mixed with 5% by volume of hydrogen is employed. The flow rate of the reducing gas G is 10 liters / minute at which the silicon powder 12 can be smoothly dissolved in the molten silicon 13 without causing the powder silicon 12 to be wound up by the reducing gas G.

Around the outer periphery from the lower part of the crucible 11 to the lower opening part 11b, a high frequency induction coil 14 having a structure in which cooling water flows inside the copper is spaced apart from the outer peripheral surface of the crucible 11 by several mm to several cm. .
The conductive cylinder 16 is a graphite cylinder having an inner diameter larger than the outer diameter of the lower opening 11 b and smaller than the inner diameter of the high-frequency induction coil 14. The upper end portion of the conductive cylinder 16 is gradually enlarged in diameter toward the top in accordance with the inclination of the funnel portion of the lower opening 11b.
The electric cylinder 17 is a vertically long actuator into which the rod 17a is put in and out. The rod 17 a has a horizontally bent upper end connected to a part of the outer peripheral surface of the conductive cylinder 16. By inserting and removing the rod 17a by the electric cylinder 17, the conductive cylinder 16 is taken in and out of the high frequency electromagnetic field.
The silicon block 15 is a disk-shaped block made of polycrystalline silicon and having a thickness of 10 mm.

Next, a method for producing granular silicon using the granular silicon production apparatus of Example 1 will be described.
First, the rod 17a is protruded by the electric cylinder 17, and the conductive cylinder 16 is disposed between the high frequency induction coil 14 and the lower opening 11b (within the high frequency AC electric field). Specifically, the conductive cylinder 16 is located at a position where the upper opening of the conductive cylinder 16 faces the lower end of the funnel portion, and the lower opening of the conductive cylinder 16 faces the vicinity of the lower opening of the cylindrical portion. Is placed. By disposing the conductive cylinder 16 in such a position, it is arranged at the uppermost part at the start of melting to shorten the melting start time, and after a stable molten silicon flow is obtained, the lower opening is not closed so long as it is not blocked. Lowering and delaying crucible degradation.

Next, the high-frequency induction coil 14 is energized (frequency 100 kHz, output 40 KW). The generated high-frequency magnetic field acts on the conductive cylinder 16 made of graphite, and the conductive cylinder 16 with eddy current loss and hysteresis loss is heated to 1000 ° C. At that time, due to the radiant heat of the conductive cylinder 16, the temperature of the outer peripheral portion of the silicon block 15 in the lower opening rises to about several hundred degrees, and the induced current starts to flow directly. A silicon melt is formed by the induced current flowing in the silicon block 15, and a part of the powder silicon 12 is dissolved in the melt.
Thereafter, the rod 17a of the electric cylinder 17 is pulled in, the conductive cylinder 16 is extracted from between the high-frequency induction coil 14 and the lower opening 11b, and the molten silicon 13 whose electrical resistivity is reduced by heating is directly High frequency induction heating is performed by the high frequency induction coil 14.

Thus, even when high-purity silicon is employed as the raw material for the powder silicon 12, the granular silicon 19 can be continuously produced from the start of production without using the preheating device employed in the conventional method. Further, since the crucible 11 having a narrowed shape is employed, the crucible 11 can be reduced in size. Moreover, since the heating range of the crucible 11 by the high-frequency induction coil 14 is limited to the vicinity of the constricted lower opening, compared with the case where a cylindrical crucible or rectangular crucible having a constant cross-sectional area over the entire length in the height direction is used. Thus, the heating volume of the crucible 11 is reduced. As a result, it is possible to reduce the power used during high-frequency induction heating compared to the case where such a crucible is used. Further, since the inner diameter of the lower opening 11b is 6 mm, the surface area of the heated portion is 1/5 or less compared to a cylindrical crucible for obtaining the same amount of silicon melt flow, and the thermal efficiency is increased by an order of magnitude. can get.
Note that after the silicon block 15 is melted, the heating of the molten silicon 13 using the radiant heat of the conductive cylinder 16 is continued without necessarily removing the conductive cylinder 16 from between the high-frequency induction coil 14 and the lower opening 11b. It may be.

Next, a granular silicon manufacturing method and apparatus according to Embodiment 2 of the present invention will be described with reference to FIG.
As shown in FIG. 2, the feature of the granular silicon manufacturing apparatus 20 according to the second embodiment is that the granular silicon 19 immediately after dropping from the lower opening 11b rolls on the slope immediately below the lower opening 11b of the crucible 11. The cooling inclined plate 21 is provided while being cooled.
The cooling inclined plate 21 is a plate made of quartz and having a gradually increasing curvature as it goes downward. The granular silicon 19 dropped from the lower opening of the crucible 11 is spheroidized by surface tension, and then gradually cooled while rolling on the inner surface of the grain cooling inclined plate 21. Thereby, the deformation | transformation by the impact at the time of the granular silicon | silicone 19 before solidifying completely colliding with the bottom plate of the collection container which is not shown in figure can be prevented, for example. In addition, since the pressure when the granular silicon 18 collides with the bottom plate becomes a fraction, the possibility that impurities are mixed into the granular silicon 19 is reduced.
Other configurations, operations, and effects are the same as those in the embodiment, and thus description thereof is omitted.

It is a longitudinal cross-sectional view of the granular silicon manufacturing apparatus which concerns on Example 1 of this invention. It is a principal part longitudinal cross-sectional view of the granular silicon manufacturing apparatus which concerns on Example 2 of this invention.

10,20 Granular silicon production equipment,
11 crucible,
11a upper opening,
11b Lower opening,
12 powder silicon,
13 Molten silicon,
14 high frequency induction coil,
15 silicon block,
16 Conductive cylinder,
17 Electric cylinder (insertion and removal means),
18 stirring nozzle,
19 granular silicon,
21 cooling inclined plate,
G reducing gas.

Claims (5)

  A crucible having a constricted shape in which powder silicon is charged from an upper opening, and molten silicon after melting of the powder silicon is continuously dropped from a lower opening,
  A high-frequency induction coil disposed around the lower opening;
  A lower opening of the crucible having a constricted shape in which the powdered silicon is accommodated by the radiant heat, which is provided between the high frequency induction coil and the lower opening so as to be detachable and heated by activation of the high frequency induction coil. A silicon block for closing the part and a conductive cylinder for auxiliary heating for melting a part of the powdered silicon,
  The granular silicon manufacturing apparatus provided with the insertion / extraction means which inserts / extracts this conductive cylinder between the said high frequency induction coil and the said lower opening part.   The granular silicon manufacturing apparatus according to claim 1, further comprising a stirring nozzle that blows a reducing gas onto the molten silicon while stirring the powdered silicon in the crucible.   3. The granular structure according to claim 1, wherein a cooling inclined plate is provided immediately below the lower opening of the crucible, in which granular silicon immediately after dripping and solidifying from the lower opening is cooled while rolling on the inclined surface. Silicon manufacturing equipment.   The granular silicon manufacturing apparatus according to any one of claims 1 to 3, wherein an opening diameter of a lower opening of the crucible is 5 to 20 mm.   A lid-stopping process in which the lower opening of the crucible having a constricted shape containing powdered silicon is closed with a silicon block;
  After the capping step, the conductive cylinder for auxiliary heating made of a conductive material arranged around the lower opening is induction-heated by high frequency, and the radiant heat causes the silicon block and the powder silicon in the lower opening to Initial melting step of partially melting and continuously dropping molten silicon from the lower opening;
  After the initial melting step, the molten silicon in the lower opening is continuously heated by radiant heat of the conductive cylinder, or the conductive cylinder is removed and the molten silicon in the lower opening is heated by high-frequency induction, and the lower opening A granular silicon manufacturing method comprising: a melting step of sequentially melting the powdered silicon that has reached the inside of the lower opening with continuous dripping of molten silicon from the substrate by heat of the molten silicon.

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