JP4258973B2 - Crystalline silicon production equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystalline silicon manufacturing apparatus that cools and gradually solidifies a silicon melt in one direction.
[0002]
[Prior art]
Polycrystalline silicon solar cells are the most commonly produced solar cells today. The most important performance of a power generation element (solar cell) of a polycrystalline silicon solar cell is energy conversion efficiency. This energy conversion efficiency greatly depends on the crystal grain boundaries of the substrate and the crystal orientation in the crystal grains. These are for reducing the energy conversion efficiency due to the shortening of the life of the carrier in the solar cell and the decrease of the mobility. Therefore, in order to improve the energy conversion efficiency, in the manufacture of polycrystalline silicon, the crystal grain boundary is reduced as much as possible, in other words, the crystal grain size is grown as large as possible, and It is important to improve the orientation.
[0003]
A typical method for producing polycrystalline silicon is a unidirectional solidification method. In this method, for example, in an argon gas atmosphere, as shown in FIG. 4, the silicon raw material S is contained in a mold 51 formed in a substantially rectangular parallelepiped shape, and this is performed by an upper heater 52 and a lower heater 53 that are separated from the mold 51. It is generated by melting the silicon raw material S to form a molten metal 54, then releasing the heating by the lower heater 53 and extracting the mold 51 from the bottom surface side by the cooling plate 55 to solidify it. The ingot generated at this time adjusts the cooling plate 55 and the heaters 52 and 53 to give a positive temperature gradient in the molten metal 54 from the bottom to the top of the mold 51, and gradually cools the molten metal 54 from the bottom.・ Grow crystals upward by solidifying. According to this method, it is known that a polycrystalline silicon ingot having a crystal grain size of several millimeters or more sufficient as a solar cell wafer can be obtained.
[0004]
At this time, in order to generate an ingot having good unidirectional solidification, it is ideal that all the heat removal from the mold 51 is performed from the bottom surface side and not from the side wall surface 51a side. Therefore, a heat insulating material 56 is provided around the cooling plate 55 outside the side wall surface 51 a of the mold 51.
Moreover, the ingot produced | generated at once shall be about 100 kg or more.
[0005]
[Problems to be solved by the invention]
However, in the conventional crystalline silicon manufacturing apparatus 50 that employs the above-mentioned unidirectional solidification method, there is a demand for shortening the cooling time because the molten metal 54 to be cooled at a time is about 100 kg or more.
[0006]
The present invention has been made in view of the above circumstances, and intends to achieve the object of shortening the manufacturing time in the manufacture of polycrystalline silicon, in particular, the cooling time of the molten metal.
[0007]
[Means for Solving the Problems]
In the crystalline silicon manufacturing apparatus of the present invention, a mold for containing a molten metal obtained by melting a silicon raw material, a heating means for heating the silicon raw material to generate a molten metal, and a lattice portion and the lattice portion are vertically penetrated. and a transmembrane portion, and a chill plate capable cooling of the mold by thermal radiation downward from said penetrating portion upon cooling the mold is placed on the grid unit, the heating means, the chill A plurality of heaters disposed below the plate, and when viewed in plan, the number of the heaters disposed on the center side of the mold is the number of the heaters disposed on the periphery side of the mold. The above-mentioned problem has been solved by setting the number to be smaller than the number .
[0008]
In the crystalline silicon manufacturing apparatus of the present invention, since the mold is placed on a lattice-shaped chill plate, the mold can be supported by the lattice portion, and heat is conducted from the mold to the chill plate during cooling. In addition, the cooling time can be shortened compared to cooling only by heat conduction to the chill plate because it can be directly cooled by heat radiation from the penetration part of the chill plate. Become.
Furthermore, since the surface area at the bottom position of the mold can be increased by the lattice portion 8a, the heat radiation efficiency can be further improved and the cooling time can be further shortened.
[0009]
Also, with the above configuration, even during heating, the heat from the heating means located on the lower side of the chill plate first heats the chill plate, and then heat conduction from the heated chill plate causes the mold to Compared to heating the silicon raw material inside, not only is the heat transferred from the chill plate to the mold, but also it can be heated directly from the through part of the chill plate by thermal radiation. The heating time can be shortened compared to the case where heating is performed only by heat conduction from the plate.
[0010]
Here, the lattice portion of the chill plate has a strength that can support the mold and is configured to have a through portion that penetrates the chill plate in the vertical direction so as to transmit heat through the chill plate. Any shape is acceptable.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a crystalline silicon manufacturing apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a front sectional view showing an embodiment of a crystalline silicon manufacturing apparatus according to the present embodiment, FIG. 2 is an enlarged front sectional view showing the vicinity of the chill plate in FIG. 1, and FIG. 1 is a crystal silicon manufacturing apparatus.
[0012]
As shown in FIG. 1, the crystalline silicon manufacturing apparatus 1 has a crucible (mold) 4 for containing a silicon melt 3, a container 5 for containing the crucible 4, and a crucible 4 accommodated in a chamber 2. A lattice-shaped chill plate 8 on which the container 5 is placed, a crucible 4, a container 5, a surrounding furnace 6 that surrounds the chill plate 8, and an upper position and a lower position of the crucible 4 in the surrounding furnace 6. Then, it is configured to have an upper heating portion 7a and a lower heating means 7b for heating the solid silicon (silicon raw material) 3a to generate a silicon melt (molten metal) 3.
[0013]
A hollow portion 2a is formed inside the wall constituting the chamber 2, and the cooling of the chamber 2 after melting the solid silicon 3a and the inside thereof can be efficiently performed by flowing cooling water therethrough. .
[0014]
The surrounding furnace 6 has a top plate portion, a bottom plate portion, and side plate portions surrounding the periphery of the top plate portion, the bottom plate portion, and the periphery thereof, and is formed in a cylindrical shape as shown in FIG. It has a square shape. A support portion 64 is provided opposite to the lower portion of the surrounding furnace 6, and the container 5 is supported on the support portion 64 via the chill plate 8.
An inflow nozzle is piped through the top plate portion of the surrounding furnace 6 through the top plate portion. The inflow nozzle allows argon gas, which is an inert gas, to flow into the surrounding furnace 6, and the distance to the silicon melt 3 can be changed by driving an elevating mechanism installed outside the chamber 2. .
[0015]
The upper heating unit 7 a is composed of a plurality of heaters arranged along the length direction of the crucible 4. Further, the lower heating part 7 b is located below the chill plate 8 and is disposed between the support parts 64 of the surrounding furnace 6. These upper heating part 7a and lower heating part 7b form a heating means. In addition, as shown in FIGS. 1 and 2, the lower heating sections 7 b and 7 b have a number of heaters arranged on the center side of the crucible 4 in a plan view as compared with the peripheral side of the crucible 4. It is arranged to be less.
[0016]
As shown in FIGS. 1 to 3, the chill plate 8 has a rectangular lattice shape in plan view, and is configured to have through portions 8b and 8b penetrating vertically between the lattice portions 8a and 8a. ing.
The container 5 is placed on the chill plate 8 in close contact with the chill plate 8. The container 5 made of carbon has a bowl shape having a side wall portion 5a and a bottom portion 5b, and the crucible 4 is accommodated therein. The side wall part 5 a is provided so as to surround the periphery of the side wall part of the crucible 4, and the upper end thereof is set to be at least a position higher than the liquid level of the silicon melt 3. The bottom portion 5 b is in close contact with the lattice portion 8 a of the chill plate 8 and the bottom portion of the crucible 4. It is also possible to place the crucible 4 directly on the chill plate 8 without installing the container 5.
[0017]
A heat absorbing plate 13 is provided below the chill plate 8 of the surrounding furnace 6. The heat absorbing plate 13 is for absorbing the radiant heat in the surrounding furnace 6 when the silicon melt 3 is cooled, and is attached to a position facing the chill plate 8 in the lower part of the chamber 2 and is made of carbon. . A lower opening is formed in the surrounding furnace 6 at a position below the mounting table 5, and a shutter that can be opened and closed is provided in the lower opening. In this shutter, the lower opening is closed when the solid silicon 3a is heated, and the shutter is opened when the silicon melt 3 is cooled.
[0018]
Further, the heat absorbing plate 13 forms a cooling water passage 14 for cooling water flowing through the chamber 2. That is, the endothermic plate 13 is arranged with an appropriate space with the bottom surface of the chamber 2, and the cooling water channel 14 is formed in the chamber 2 by the space between the hollow portion 2 a in the chamber 2 and the bottom surface of the chamber 2 and the endothermic plate 13. It is formed so as to surround the whole.
A cooling nozzle 21 that penetrates the chamber 2 and the heat absorbing plate 13 is provided at the bottom of the chamber 2. The cooling nozzle 21 flows into the surrounding furnace 6 from below so that argon gas is blown toward the chill plate 8 when the silicon melt 3 is cooled.
[0019]
Furthermore, an upper opening is provided in the upper part of the side plate portion of the surrounding furnace 6, and an upper opening / closing mechanism for opening and closing the upper opening is also provided. The upper opening / closing mechanism includes an opening / closing door and an actuator connected to the opening / closing door. When the solid silicon 3a is heated, the opening / closing door is in a state of closing the upper opening, and when the silicon melt 3 is cooled, the opening / closing door is opened by driving the actuator. Furthermore, an exhaust port 22 is piped on the upper part of the surrounding furnace 6 and the chamber 2. This exhaust port 22 is for exhausting the argon gas when it flows into the surrounding furnace 6 from the lower cooling nozzle 21 or the like when the silicon melt 3 is cooled. The surrounding furnace 6 is provided with a view port for observation, a temperature sensor, a port through which wirings of the heating means 7a and 7b are passed, and the like.
[0020]
When crystal silicon is manufactured using the crystal silicon manufacturing apparatus 1 having the above-described configuration, first, raw material chip-shaped solid silicon 3 a is accommodated in the crucible 4.
Next, the shutter and the upper opening / closing door are closed, and argon gas flows into the surrounding furnace 6 from the inflow port 20 to maintain a gas atmosphere at a predetermined pressure, and in this state, the upper heating unit 7a and the lower heating unit 7b are operated. The temperature in the surrounding furnace 6 is increased.
Then, the crucible 4 is heated by the radiant heat from the lower heating part 7b that has passed through the penetration part 8b and the heat conduction from the chill plate 8, and at the same time, the solid silicon 3a in the crucible 4 is melted by being heated from the upper heating part 7a. To do. When the melting temperature is reached, the silicon melt 3 is generated. The melting temperature of silicon is 1480 ° C.
[0021]
When the silicon melt 3 is generated, the operation of the lower heating unit 7b is stopped while the upper heating unit 7a remains in an operating state, and when the shutter is opened, heat is conducted from the crucible 4 to the chill plate 8 to be cooled. At the same time, the heat absorbing plate 13 directly absorbs heat from the penetrating portion 8b of the chill plate 8 as indicated by an arrow in FIG.
At the same time, the heat in the surrounding furnace 6 is absorbed by the heat absorbing plate 13 from the lower opening. As a result, the inside of the surrounding furnace 6 is lowered from the melting temperature of silicon to about 1000 ° C. Then, when the lower part in the surrounding furnace 6 falls to 1000 ° C. or lower, the silicon melt 3 in the crucible 4 starts to solidify. When the silicon melt 3 starts to solidify and the operation of the upper heating unit 7a is also stopped, the silicon melt 3 in the crucible 4 is gradually solidified from the lower part to the upper part.
As described above, by applying a positive temperature gradient from the bottom of the crucible 4 to the upper side and cooling the silicon melt 3, silicon is solidified and crystallized.
[0022]
In this embodiment, as shown by the arrow in FIG. 2, the heat absorbing plate 13 directly absorbs heat from the through portions 8b between the lattice portions 8a of the chill plate 8 to, for example, a chill plate having no through portions. The cooling time can be shortened by about 1 hour as compared with the case where cooling is performed only by heat conduction.
In addition, during heating, not only the crucible 4 is heated by conduction from the lattice portion 8a of the chill plate 8 but also when the heating from the lower heating portion 7b located on the lower side of the chill plate 8 is performed, the chill plate 8 Since it is possible to heat from the through portion 8b of the lower heating portion 7b by heat radiation, compared with the case of heating the solid silicon 3a inside the crucible 4 only by heat conduction from the chill plate without the through portion, It is possible to shorten the heating time.
[0023]
At this time, in the lower heating part 7b located below the chill plate 8, the number of the crucible 4 center side is smaller than that of the crucible 4 peripheral part in plan view. Since the heat radiated from the penetrating portion 8b of the plate 8 can be efficiently absorbed by the heat absorbing plate 13, the efficiency of heat radiation can be increased and the cooling time can be further shortened.
[0024]
【The invention's effect】
According to the crystalline silicon manufacturing apparatus of the present invention, the mold is placed on the lattice-shaped chill plate so that the mold can be supported by the lattice portion, and at the time of cooling, heat is conducted from the mold to the chill plate to cool the mold. In addition, the cooling time can be shortened compared to the case of cooling only by heat conduction to the chill plate without the through portion because it can be directly cooled by the heat radiation from the through portion of the chill plate. At the same time, it is possible not only to heat by heat conduction from the chill plate to the mold, but also to directly heat by heat radiation from the piercing portion of the chill plate during heating. The heat from the heating means located on the lower side first heats the chill plate without the penetrating part, and then casts by heat conduction from the chill plate As compared with the case of heating the interior of the silicon material, an effect that it becomes possible to shorten the heating time.
[Brief description of the drawings]
FIG. 1 is a front sectional view showing an embodiment of an apparatus for producing crystalline silicon according to the present invention.
2 is an enlarged front sectional view showing the vicinity of the chill plate of the crystalline silicon manufacturing apparatus of FIG. 1. FIG.
3 is a plan view showing a chill plate of the crystalline silicon manufacturing apparatus of FIG. 1. FIG.
FIG. 4 is a schematic diagram showing a conventional crystalline silicon manufacturing apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Crystal silicon production apparatus 2 ... Chamber 3 ... Silicon melt (molten metal)
3a: Solid silicon (silicon raw material)
4 ... Crucible (mold)
5 ... Container 5a ... Side wall 6 ... Surrounding furnace 8 ... Chill plate 8a ... Lattice part 8b ... Penetration part

Claims (1)

Has a mold which accommodates the molten metal by melting the silicon raw material, a heating means for generating a molten metal by heating a silicon material, a pierced penetrating portion up and down between the grating portion and the grating portion, the mold A chill plate placed on the grid portion and capable of cooling the mold by thermal radiation downward from the penetrating portion during cooling , and
The heating means includes a plurality of heaters disposed below the chill plate, and when viewed in plan, the number of heaters disposed on the center side of the mold is on the peripheral side of the mold. An apparatus for producing crystalline silicon, wherein the apparatus is set to be smaller than the number of heaters provided .

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