JP4611507B2 - 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 manufactured 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 by shortening the lifetime of the carrier in the solar cell and reducing 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, the chamber in which the crucible is arranged is filled with an inert gas such as argon gas, and the solid silicon of the raw material contained in the crucible is heated by heating means arranged above and below the crucible to obtain a silicon melt, Next, the heating means below the crucible is stopped, and the inert gas is blown to the bottom of the crucible while being circulated to give a positive temperature gradient from the bottom of the crucible upward to the silicon melt. Then, the silicon melt is gradually cooled and solidified from the bottom to grow the crystal upward. 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]
[Problems to be solved by the invention]
However, in the above-mentioned unidirectional solidification method, solid silicon is heated by a heating means to generate a silicon melt, but there is a problem that it takes a long time to generate the silicon melt.
[0005]
In view of the above circumstances, an object of the present invention is to provide a crystalline silicon manufacturing apparatus that can shorten the melting time of solid silicon.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs the following means.
In the present invention, a crucible for containing a silicon melt in a chamber, a placing table for placing the crucible, an enclosing furnace for enclosing the crucible and the placing table, and solid silicon contained in the crucible are heated to form silicon. A crystalline silicon manufacturing apparatus that solidifies the silicon melt in the crucible unidirectionally from the bottom to the top, and the heating unit is positioned above the crucible in the surrounding furnace. It has an upper heating part arranged, and at least the inner surface of the top plate part of the surrounding furnace is provided with a heat reflecting film for increasing the heat reflectivity in the surrounding furnace.
[0007]
When the heat reflecting film is provided on the inner surface of the surrounding furnace in this way, when the solid silicon is heated and melted, the heat reflecting film increases the heat reflectivity in the surrounding furnace, and the inside of the surrounding furnace is melted with the solid silicon. Since the silicon melt can be generated in such a short time, the time for melting the solid silicon can be surely shortened.
[0008]
The heat reflection film is preferably provided on the inner surface of the upper half of the surrounding furnace, and is preferably not provided on the inner surface of the lower half of the surrounding furnace. There is no risk of inhibiting the action.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1 and FIG. 2, the crystalline silicon manufacturing apparatus 1 includes a crucible 4 for containing a silicon melt 3, a mounting table 5 for mounting the crucible 4, a crucible 4 and a mounting table. An enclosing furnace 6 that surrounds 5, and an upper heating section 7 a and a lower heating section 7 b that are respectively disposed above and below the crucible 4 within the enclosing furnace 6 and that heat the solid silicon 3 a to generate the silicon melt 3. And are provided.
[0010]
A hollow portion 2a is formed inside the wall constituting the chamber 2, and cooling water is allowed to flow therethrough to efficiently cool the chamber 2 after melting the solid silicon 3a and the inside thereof. . The mounting table 5 mounts the crucible 4 via a heat insulating material 5a.
[0011]
As shown in FIG. 2, the surrounding furnace 6 has a top plate portion 61, a bottom plate portion 62, and a side plate portion 63 surrounding the periphery of the top plate portion 61, a bottom plate portion 62, and a side plate portion 63 surrounding them. As shown in FIG. 2, it has a cylindrical shape as shown in FIG. Further, support portions are provided opposite to each other in the lower part of the surrounding furnace 6, and the mounting table 5 is supported on the support portions via the chill plate 8. An inflow nozzle 20 is piped through the top plate 61 in the top plate 61 of the surrounding furnace 6. The inflow nozzle 20 allows argon gas, which is an inert gas, to flow into the surrounding furnace 6 and is installed outside the chamber 2 so that the distance to the silicon melt 3 can be changed by driving the elevating mechanism 20a. ing.
[0012]
The upper heating unit 7 a and the lower heating unit 7 b are constituted by a plurality of heaters arranged along the length direction of the crucible 4. The lower heating part 7 b is located below the chill plate 8 and is disposed between the support parts of the surrounding furnace 6.
[0013]
The surrounding furnace 6 has a lower opening 9 formed at a position below the mounting table 5 and has a lower opening / closing mechanism 10 for opening and closing the lower opening 9. The lower opening / closing mechanism 10 includes a shutter 11 that opens and closes the lower opening 9 and an actuator 12 that opens the shutter 11 in a direction away from each other along the bottom surface of the bottom plate portion 62 of the surrounding furnace 6. When the silicon melt 3 is cooled, the actuator 12 is released and the shutter 11 is opened when the shutter 11 is closed by the actuator 12 being driven. The shutter 11 is also made of carbon so as to perform a heat insulating function.
[0014]
An endothermic plate 13 is provided at a position below the shutter 11 of the surrounding furnace 6. The heat absorbing plate 13 is for absorbing the radiant heat in the surrounding furnace 6, and is attached to a position facing the lower opening 9 and the shutter 11 in the lower part of the chamber 2 and is made of carbon.
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.
[0015]
Further, as shown in FIG. 2, the surrounding furnace 6 has an upper opening 15 provided on the upper side of the side plate portion 63, and also has an upper opening / closing mechanism 16 that opens and closes the upper opening 15. The upper opening / closing mechanism 16 includes an opening / closing door 17 attached to the outer surface of the side plate portion 63 via a hinge so as to be opened and closed, and an actuator 18 connected to the opening / closing door 17 via a pivot joint 19. When the solid silicon 3a is heated, the open / close door 17 keeps the upper opening 15 of the side plate portion 63 closed as shown by the solid line in FIG. 2, and when the silicon melt 3 is cooled, the actuator 18 is driven to open and close the door. The door 17 is opened as shown by the chain line.
[0016]
Furthermore, an exhaust port 22 is piped on the upper part of the surrounding furnace 6 and the chamber 2. When the silicon melt 3 is cooled, the exhaust port 22 prevents the gas A from staying in the surrounding furnace 6 when argon gas flows into the surrounding furnace 6 from below. 1 and FIG. 3, four surrounding furnace port portions piped through the side plate portion 63 of the surrounding furnace 6, and the chamber 2, as shown in FIGS. 1 and 3. It consists of two chamber port portions that are piped at a position facing the upper opening 15.
The port portion for the surrounding furnace in this example is piped at an appropriate angle along the circumference of the surrounding furnace 6 in the same direction, and the chamber port portion is also inclined at an angle according to the port portion for the surrounding furnace. It is piped.
[0017]
On the other hand, a heat reflecting film 51 is provided on the inner surface of the surrounding furnace 6. The heat reflecting film 51 is for increasing the reflectance of heat in the surrounding furnace 6 while lowering the radiation rate, and the surface has a metallic surface gloss. In this example, Nippon Carbon Co., Ltd. "Carbon coating FGL-203" manufactured by the manufacturer is employed.
Since this heat reflection film 51 needs to be cooled upward from the lower part of the surrounding furnace 6 when the silicon melt 3 is cooled, it is provided at least on the entire inner surface of the top plate part 61 of the surrounding furnace 6, and the side plate part It is desirable not to be provided on the inner surface of the lower half of the side plate portion 63 or the bottom plate portion 62 so that the cooling efficiency is not lowered.
In FIG. 1, 23 is a view port for observation, 24 is a temperature sensor, and 25 is a port through which wirings of the upper and lower heating units 7a and 7b are passed.
[0018]
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. At this time, the shutter 11 of the lower opening / closing mechanism 10 closes the lower opening 9 as shown in FIG. 1, and the opening / closing door 17 of the upper opening / closing mechanism 16 closes the upper opening 15 of the surrounding furnace 6.
Next, argon gas is flowed into the surrounding furnace 6 from the inflow port 20 and maintained in a gas atmosphere at a predetermined pressure. In this state, the upper heating section 7a and the lower heating section 7b are operated to raise the temperature in the surrounding furnace 6; When the melting temperature is reached, the solid silicon 3a in the crucible 4 is melted, whereby the silicon melt 3 is generated. Incidentally, the melting temperature of silicon is 1480 ° C.
[0019]
When the heat reflecting film 51 is provided on the inner surface of the surrounding furnace 6 at the time of the heating and melting, the heat reflecting film 51 can increase the reflectance of the heat in the surrounding furnace 6 and reduce the radiation rate. By raising the inside of the furnace 6 as quickly as possible to the melting temperature of the solid silicon 3a and generating the silicon melt 3 in such a short time, the melting time of the solid silicon 3a can be surely shortened. .
[0020]
When the silicon melt 3 is generated, the silicon melt 3 is cooled, so that silicon is solidified and crystallized.
At the time of the cooling, in order to solidify the silicon melt 3 in the crucible 4 in one direction from the lower part to the upper part, the upper heating part 7a is kept in an activated state, and the lower heating part 7b is stopped to operate. When the shutter 11 is opened, the heat in the surrounding furnace 6 is absorbed by the heat absorbing plate 13 from the lower opening 9. Thereby, the inside of the surrounding furnace 6 falls from the melting temperature of silicon to about 1000 ° C.
[0021]
In this case, the heat reflecting film 51 is provided on the entire inner surface of the top plate portion 61 of the surrounding furnace 6 and also on the inner surface of the upper half of the side plate portion 63, and the inner surface of the lower half of the side plate portion 63 and the bottom plate portion 62. Therefore, when the silicon melt 3 is cooled from below, the cooling action is not hindered and the cooling efficiency is not lowered.
[0022]
Further, at the time of cooling, the cooling water flows through the hollow portion 2 a of the chamber 2, so that the heat in the surrounding furnace 6 is transferred from the heat absorbing plate 13 to the cooling water in the chamber 2 and the chamber 2.
In this case, argon gas flows in from below through the cooling port 21 and rises while cooling the chill plate 8 side, while the argon gas in the surrounding furnace is exhausted from the surrounding furnace port portion , The heat is discharged together with argon gas.
[0023]
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, the operation of the upper heating unit 7a is also stopped, so that the silicon melt 3 in the crucible 4 is gradually solidified from the lower part to the upper part.
Further, the opening / closing door 17 of the upper opening / closing mechanism 16 is opened, and the heat in the surrounding furnace 6 is also dissipated from the upper opening 15 into the space between the chamber 2 and the surrounding furnace 6 so that the entire inside of the surrounding furnace 6 is argon. Cooled by endothermic gas. In this case, the gas in the surrounding furnace 6 flows into the chamber 2 from the upper opening 15, but is exhausted from the chamber port through the space in the chamber 2.
[0024]
【The invention's effect】
As described above, according to the present invention, the heat reflecting film is provided on the inner surface of the surrounding furnace, and when the solid silicon is heated and melted, the heat reflecting film increases the reflectance of the heat in the surrounding furnace, Since the temperature can be raised to the melting temperature of the solid silicon as quickly as possible, the silicon melt can be generated in a short time, so that the melting time of the solid silicon can be surely shortened, As a result, the production time of the crystalline silicon ingot is accelerated.
[0025]
Further, according to the present invention, the heat reflecting film is preferably provided on the inner surface of at least the upper half in the surrounding furnace, and when cooling the silicon melt from the lower part, the cooling action is not hindered and the cooling efficiency is reduced. There is an effect that there is no fear of lowering.
[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.
FIG. 2 is a side sectional view of the crystalline silicon manufacturing apparatus of FIG.
FIG. 3 is an enlarged sectional view showing a part of the wall of the surrounding furnace.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Crystalline silicon manufacturing apparatus 2 Chamber 3 Silicon melt 4 Crucible 5 Mounting stand 6 Surrounding furnace 7a Upper heating part 7b Lower heating part 10 Lower opening / closing mechanism 11 Shutter 12 Actuator 13 Endothermic plate 51 Heat reflecting plate

Claims (2)

A crucible for containing the silicon melt in the chamber, a mounting table for mounting the crucible, a surrounding furnace for enclosing the crucible and the mounting table, and solid silicon stored in the crucible are heated to generate a silicon melt. A crystalline silicon manufacturing apparatus that solidifies the silicon melt in the crucible unidirectionally upward from the bottom ,
The heating unit has an upper heating unit disposed at an upper position of the crucible in the surrounding furnace,
An apparatus for producing crystalline silicon , wherein a heat reflecting film for increasing heat reflectivity in the surrounding furnace is provided at least on the entire inner surface of the top plate portion of the surrounding furnace. 2. The crystalline silicon manufacturing apparatus according to claim 1, wherein the heat reflecting film is provided on the inner surface of the upper half of the surrounding furnace and is not provided on the inner surface of the lower half of the surrounding furnace .

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