JP2002211913A - Apparatus for producing crystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten heating time and to diminish the effect of leaking molten silicon. SOLUTION: The apparatus for producing crystalline silicon has a casting mold 4 housing molten silicon 3, a chilling plate 8 which supports the casting mold 4 put thereon, has electric conductivity and generates heat when an electric current is sent to the chilling plate 8 and a power source 9 for sending the electric current to the chilling plate 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing crystalline silicon in which a silicon melt is cooled and gradually solidified in one direction.

[0002]

2. Description of the Related Art Polycrystalline silicon solar cells are the most widely manufactured solar cells today. The most important performance of a polycrystalline silicon solar cell power generation element (solar cell) is energy conversion efficiency. The energy conversion efficiency largely depends on the crystal grain boundaries of the substrate and the orientation of crystals in the crystal grains. These are for shortening the life of carriers in the solar cell and decreasing the mobility, thereby lowering the energy conversion efficiency. Therefore, in order to improve the energy conversion efficiency, in the production of polycrystalline silicon, the crystal grain boundaries are reduced as much as possible, in other words, the crystal grain size is grown to be as large as possible. It is important to improve the orientation of.

A typical method for producing polycrystalline silicon is a unidirectional solidification method. In this method, for example, as shown in FIG. 3, a silicon raw material S contained in a substantially rectangular parallelepiped mold 51 is melted by an upper heater 52 and a lower heater 53 separated from the mold 51 to form a molten metal 54. Then, the heating by the lower heater 53 is released, and the mold 51 is generated by removing the heat from the bottom side of the mold 51 by the cooling plate 55 and solidifying. The ingot generated at this time adjusts the cooling plate 55 and the heaters 52 and 53 to give a positive temperature gradient from the bottom to the top of the mold 51 in the molten metal 54 so that the molten metal 54 is gradually cooled from the bottom. -The crystal is grown upward by solidification. According to this method, it is known that a polycrystalline silicon ingot having a crystal grain size of several millimeters or more, which is sufficient for a solar cell wafer, can be obtained.

At this time, in order to produce an ingot having good unidirectional solidification, it is ideal that all heat is removed from the mold 51 from the bottom side and not from the side wall 51a. Therefore, outside the side wall surface 51a of the mold 51,
A heat insulating material 56 made of carbon is provided around the cooling plate 55. Further, the heat insulating material 56 is provided from the mold 51 to the molten metal 5.
In the case where 4 leaks, it is provided to absorb the leaked molten metal 54 so as not to affect other parts.

[0005]

However, a conventional crystalline silicon manufacturing apparatus 5 adopting the above-described directional solidification method has been proposed.
At 0, when heating and melting the silicon raw material, the temperature of the silicon raw material S in the mold 51 was increased by radiant heat from the heaters 52 and 53, but it took a long time until the silicon raw material S was completely melted. For this reason, there has been a demand for shortening the heating time. Also, the mold 51
When the molten metal 54 leaks from the container, if the amount of the leaked molten metal 54 is large, the molten metal 54 may not be completely absorbed by the heat insulating material 56. The silicon manufacturing equipment 50
There was a problem that the lower part of the was affected.

The present invention has been made in view of the above circumstances, and aims to achieve the following objects. Reduce the heating time. Reduce the effects of leaked molten metal.

[0007]

In the apparatus for producing crystalline silicon according to the present invention, a mold for holding a molten metal, and a mold placed thereon, having conductivity and being energized, generates heat during heating and cools. The above-mentioned problem has been solved by providing a chill plate that sometimes cools down and a power supply for supplying power to the chill plate. In the present invention, it is preferable that a housing for housing the mold inside is provided on the chill plate. In the present invention, the container is made of carbon, or
Means in which the chill and the plate are made of carbon may be employed.

In the apparatus for producing crystalline silicon according to the present invention, the chill plate for cooling the mold has conductivity during cooling, and when the chill plate is energized, the chill plate generates heat during heating. The mold placed on the chill plate is heated. For this reason, unlike the conventional technology in which the silicon raw material in the mold is heated only by radiant heat from the heater, heat is directly applied from the chill plate that generates heat to the mold that is in contact with the chill plate. Can be conducted. As a result, the heating time required to melt the silicon raw material in the mold can be reduced. At this time, it is also possible to use a heater for heating the mold by radiation as in the conventional technique.

In the present invention, a container is provided on the chill plate, the container having the side wall extending to a position higher than the liquid level of the molten metal so as to house the mold therein and at least surround the periphery of the side wall of the mold. Accordingly, even when the molten metal leaks from the mold, the leaked molten metal can be stored between the side wall of the mold and the side wall of the container. This prevents the molten metal from leaking out of the container,
It is possible to prevent the molten metal from affecting each part of the crystalline silicon manufacturing apparatus located below the mold. Here, the container may have a tub shape having a bottom portion and a side wall portion,
Moreover, it is also possible to integrate with the chill plate.

Further, in the present invention, by adopting a means in which the chill plate is made of carbon, it is possible to obtain conductivity and a resistance value capable of generating heat necessary for heating the mold when energized. In addition, sufficient heat conductivity can be obtained in order to conduct heat from the chill plate to the mold well. Also, by adopting a means in which the container is made of carbon,
Sufficient thermal conductivity can be obtained in order to conduct the heat from the chill plate to the mold satisfactorily, and the molten metal can be stored inside.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a crystalline silicon manufacturing apparatus according to the present invention will be described below with reference to the drawings. Figure 1
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 view showing the vicinity of a chill plate in FIG. 1, and reference numeral 1 in FIG. 1 is a crystalline silicon manufacturing apparatus. .

As shown in FIG. 1, a crystalline silicon manufacturing apparatus 1 includes a crucible (mold) 4 for accommodating a silicon melt 3 in a chamber 2, a container 5 for accommodating the crucible 4,
A chill plate 8 on which the container 5 accommodating the crucible 4 is placed; an enclosing furnace 6 surrounding the crucible 4, the container 5 and the chill plate 8; And an upper heating unit 7a for heating the solid silicon (silicon raw material) 3a to generate a silicon melt 3 (melt).

A hollow portion 2a is formed inside a wall constituting the chamber 2, and cooling water is supplied to the hollow portion 2a so that the chamber 2 after the solid silicon 3a is melted and the inside thereof can be efficiently cooled. Has become.

The surrounding furnace 6 is made of a plurality of heat insulating materials and has a top plate, a bottom plate, and side plates surrounding them. For example, the surrounding furnace 6 has a cylindrical shape as shown in FIG. It has a square shape when viewed from the side. The surrounding furnace 6
Support portions 64 are provided opposite to each other at the lower part of the housing, and the container 5 is supported on the support portions 64 via the chill plate 8. An inflow nozzle is provided on the top plate of the surrounding furnace 6 so as to penetrate the top plate. The inflow nozzle is for letting argon gas, which is an inert gas, flow into the surrounding furnace 6.
By driving the elevating mechanism installed outside the chamber 2,
The distance to the silicon melt 3 can be changed.

The upper heating section 7a is composed of a plurality of heaters arranged along the length of the crucible 4. The chill plate 8 is made of carbon, is connected to a power supply 9, and generates heat when energized. These upper heating units 7
a, the chill plate 8 and the power supply 9 form a heating means. 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 tub shape having a side wall 5a and a bottom 5b, and the crucible 4 is accommodated therein. The side wall 5 a is provided so as to surround the periphery of the side wall of the crucible 4, and the upper end thereof is set to at least a position higher than the liquid level of the silicon melt 3. Bottom 5
b is in close contact with the chill plate 8 and the bottom of the crucible 4.

A heat absorbing plate 13 is provided below the chill plate 8 of the surrounding furnace 6. The heat absorbing plate 13 absorbs radiant heat in the surrounding furnace 6 when the silicon melt 3 is cooled, and is attached to a lower portion of the chamber 2 at a position facing the chill plate 8 and is formed 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. The lower opening is closed when the solid silicon 3a is heated, and the shutter is opened when the silicon melt 3 is cooled.

The heat absorbing plate 13 forms a cooling water passage 14 for cooling water flowing in the chamber 2. That is, the heat absorbing plate 13 is disposed with an appropriate space with the bottom surface of the chamber 2, and the cooling water passage 14 is formed in the hollow portion 2 in the chamber 2.
a and the space between the bottom surface of the chamber 2 and the heat absorbing plate 13 so as to surround the entire inside of the chamber 2.
The chamber 2 and the heat absorbing plate 13 are provided at the bottom of the chamber 2.
Is provided. When cooling the silicon melt 3, the cooling nozzle 21 flows into the surrounding furnace 6 from below so as to blow argon gas toward the chill plate 8.

Further, an upper opening is provided above 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 open / close door keeps the upper opening closed, and when the silicon melt 3 is cooled, the open / close door is opened by driving the actuator. Further, an exhaust port 22 is provided above the surrounding furnace 6 and the chamber 2. This exhaust port 22
When the argon gas flows into the surrounding furnace 6 from the lower cooling nozzle 21 or the like at the time of cooling the silicon melt 3, the gas is exhausted. In addition, in the surrounding furnace 6,
A view port for observation, a temperature sensor, a port through which wires of the upper heating unit 7a pass, and the like are provided.

When manufacturing crystalline silicon using the crystalline silicon manufacturing apparatus 1 having the above-described configuration, first, the crucible 4 is manufactured.
The raw material chip-shaped solid silicon 3a is accommodated therein. Next, argon gas is introduced into the surrounding furnace 6 from the inflow port 20 and maintained at a predetermined pressure gas atmosphere.
Is operated to energize the chill plate 8 to generate heat, and this heat is directly conducted to the crucible 4 through the contacting housing 5 as shown by the arrow in FIG. The solid silicon 3a is melted. At this time, the upper heating unit 7a is simultaneously operated to raise the temperature inside the surrounding furnace 6. When the temperature reaches the melting temperature, the solid silicon 3a in the crucible 4 is melted, so that a silicon melt 3 is generated. The melting temperature of silicon is 1480 ° C.

When the silicon melt 3 is generated,
When the power supply to the chill plate 8 is stopped while the upper heating unit 7a is kept operating and the shutter is opened, the heat in the surrounding furnace 6 is absorbed by the heat absorbing plate 13 from the lower opening. As a result, the temperature in the surrounding furnace 6 drops from the melting temperature of silicon to about 1000 ° C. When the lower part in the surrounding furnace 6 falls below 1000 ° C., the silicon melt 3 in the crucible 4 starts to solidify. When the silicon melt 3 starts to solidify, the upper heating unit 7
By stopping the operation of a, the silicon melt 3 in the crucible 4 gradually solidifies from the lower part to the upper part. In this way, by applying a positive temperature gradient from the bottom to the top of the crucible 4 and cooling the silicon melt 3, the silicon is solidified and crystallized.

In the present embodiment, the heating efficiency of the solid silicon 3a is increased by directly heating the crucible 4 via the housing 5 from the chill plate 8 serving as a heating element by energizing, instead of the radiant heat by the heater. Increase,
The heating time can be reliably reduced. Accordingly, the production cost of crystalline silicon can be reduced, and the running cost of the crystalline silicon production apparatus can be reduced.

At this time, since the chill plate 8 is made of carbon, it is possible to obtain the conductivity and resistance value capable of generating heat necessary for heating the crucible 4 when energized, and to generate heat. Sufficient thermal conductivity can be obtained to conduct heat from the chill plate 8 to the mold well.

The crucible 4 is housed inside the housing 5, and the housing 5 is located at a position higher than the liquid surface of the silicon melt 3 so as to surround at least the periphery of the side wall of the crucible 4. By having the portion 5a, even if the silicon melt 3 leaks out of the crucible 4, the silicon melt can be prevented from leaking to the outside of the container 5, so that the lower structure of the surrounding furnace 6 is affected. Can be prevented. In addition, since the container 5 is made of carbon, sufficient heat conductivity can be obtained to conduct the heat from the chill plate 8 to the crucible 4 well, and silicon at about 1480 ° C. It is possible to store the melt 3 therein.

[0024]

According to the apparatus for manufacturing crystalline silicon of the present invention, the following effects can be obtained. (1) It becomes possible to conduct heat directly from the chill plate, which is placed on the mold and is heated by supplying electricity to the chill plate having conductivity, to the mold in contact with the chill plate, As a result, the heating time required to melt the silicon raw material in the mold can be reduced, and the running cost of the crystalline silicon manufacturing apparatus can be reduced. (2) By providing a container having the side wall part located at a position higher than the liquid level of the molten metal so as to house the mold inside the chill plate and surround at least the periphery of the side wall part of the mold, Even when the molten metal leaks from the mold, the leaked molten metal can be stored between the side wall of the mold and the side wall of the container. Thus, it is possible to prevent the molten metal from leaking from the container to the outside, and to prevent the molten metal from affecting each part of the crystalline silicon manufacturing apparatus located below the mold. (3) By adopting a means in which the chill plate is made of carbon, it becomes possible to obtain conductivity and a resistance value capable of generating heat necessary for heating the mold when energized, and generate heat. Sufficient thermal conductivity can be obtained to conduct heat from the chill plate to the mold well. (4) By adopting means in which the container is made of carbon, it is possible to obtain sufficient thermal conductivity for satisfactorily conducting heat from the chill plate to the mold, and to disperse the molten metal into the mold. It can be stored inside.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing one embodiment of a crystalline silicon manufacturing apparatus according to the present invention.

FIG. 2 is an enlarged sectional view showing the vicinity of a chill plate of the crystalline silicon manufacturing apparatus of FIG.

FIG. 3 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 9 ... Power supply

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akihito Yanoo 2-4-1 Tamagawa Machinery Co., Ltd. Nagaoka Plant, Nagaoka City, Niigata Prefecture F-term (reference) 4G072 AA01 BB12 GG01 GG03 HH01 NN01 RR30 UU02 5F051 AA03 CB05

Claims (4)

[Claims] 1. A mold for holding a molten metal, a chill plate on which the mold is placed, which has conductivity and is energized, generates heat when heated and cools when cooled, and supplies electricity to the chill plate. And a power supply. 2. The crystal silicon manufacturing apparatus according to claim 1, wherein a housing body for housing the mold is provided on the chill plate. 3. The apparatus according to claim 1, wherein said chill plate is made of carbon. 4. The apparatus for producing crystalline silicon according to claim 2, wherein said container is made of carbon.