KR20130005743A - Electromagnetic continuous casting machine for manufacturing silicon ingot - Google Patents

Abstract

PURPOSE: An electromagnetic continuous casting machine for manufacturing silicon ingot is provided to prevent the generation of an impurity by reducing the contact area between molten silicon ingot and a cold crucible. CONSTITUTION: A cold crucible is arranged in the inner side of an induction coil(130). Slits(120) are vertically formed. A segment(110) is divided by the slits. The width of the segment is 20 to 50mm. A horizontal section of the cold crucible is square or rectangular shape.

Description

Electromagnetic continuous casting device for the production of silicon ingots {ELECTROMAGNETIC CONTINUOUS CASTING MACHINE FOR MANUFACTURING SILICON INGOT}

The present invention relates to an electromagnetic continuous casting device for the production of silicon ingots. More specifically, the present invention includes a bottom open cold crucible having a structure in which at least a portion of the circumferential direction is divided into segments by longitudinal slits, the molten silicon being lowered by electromagnetic induction heating by an induction coil. The present invention relates to an electromagnetic continuous casting apparatus for producing a silicon ingot for a solar cell by solidifying with a mold.

Currently, as a method of manufacturing a substrate for a solar cell, a single crystal method, a polycrystal method, a substrate growth method, and a thin film method exist. Among them, the single crystal method has been most used until the mid-1990s due to its excellent conversion efficiency, but recently, the polycrystal method has been mainly used due to the development and price problems of impurity removal technology, grain boundary processing technology, and cell processing technology.

Among polycrystalline silicon manufacturing techniques, the cast method is a method of solidifying molten silicon into a quartz crucible or graphite mold. In this method, the molten silicon and the walls of the crucible come into contact with impurities to form impurities in the silicon ingot, There is a problem that the release agent used to prevent fusion between crucibles is incorporated into the molten silicon. Moreover, since continuous casting is impossible, the fall of production efficiency is inevitable.

The electromagnetic continuous casting method is a method for continuously manufacturing a semiconductor or metal material having a relatively low electrical conductivity in an ingot form using an electromagnetic induction phenomenon. Electromagnetic induction is used to supply the heat of fusion required to melt the raw materials being supplied, or to create an electromagnetic pressure that prevents the melt from contacting the crucible wall. When the molten silicon is moved downward, the induction magnetic field becomes smaller in response to moving away from the lower end of the high frequency induction coil. Therefore, the induced current decreases and the amount of heat generated decreases, so that the silicon solidifies from the lower end of the molten silicon to the upper end, thereby inducing the silicon ingot. Is produced.

In such an electromagnetic continuous casting method, a bottom open cold crucible is used, which is composed of a segment at least partially divided by longitudinal slits along the circumferential direction. The divided segment consists of a water-cooled structure in which cooling water passes through for the purpose of solidifying the molten metal and protecting the cold crucible. Ingots produced in cold crucibles may have a cross section corresponding to the cross-sectional shape and size of the internal space of the cold crucible, and ingots formed by continuous supply of raw materials may be continuously discharged from the bottom of the cold crucible so that silicon polycrystalline ingots are continuously It can be prepared as.

The production of polycrystalline silicon ingots by electromagnetic continuous casting method minimizes impurity contamination by preventing molten silicon from contacting the inner wall of the crucible, and can continuously produce silicon ingots, thereby greatly reducing manufacturing costs. It is possible. In addition, the manufactured polycrystalline silicon ingot can improve wafer yield through the development of ultra-thin polycrystalline silicon wafer having a thickness of 150 μm or less by taking advantage of low breakage rate in the wafer processing process.

However, in the actual process, as the cross-sectional area of the ingot increases, the hydrostatic pressure of the molten silicon in the cold crucible also increases proportionally, resulting in local damage or distortion of the shape in the segments and slits constituting the cold crucible. In addition, frequent repairs are required, and the life of the crucible is shortened, resulting in lower productivity due to higher equipment costs and longer production periods for cold crucibles. The damage to the segments and slits is due to the molten silicon contacting the charged crucible inner surface and generating a discharge. As these damages increase and the slit gaps increase, the induced current generated in the molten silicon is weakened and the amount of heat for melting the raw material decreases. In addition, there is a problem that the casting becomes unstable, and the quality of the silicon ingot produced is also reduced. In addition, as the contact area between the molten silicon and the inner surface of the cold crucible increases, the concentration of the material of the cold crucible in the polycrystalline silicon wafer is increased, thereby reducing the conversion efficiency of the solar cell.

And also, in the conventional electromagnetic continuous casting apparatus, the cold crucible has been used integrally to prevent deformation of the cold crucible and to form a uniform electromagnetic induction in the molten silicon. As the cross-sectional area of the ingot increases, the hydrostatic pressure of the molten silicon in the cold crucible also increases. In this case, local damage or shape distortion occurs in the segments and slits constituting the cold crucible. Damage or distortion of some of the crucibles may require repair, shorten the life of the crucible, increase equipment costs, and reduce the productivity of the silicon ingot. When using a conventional integrated cold crucible, there is a problem in terms of cost and time because the entire cold crucible must be replaced even when only a part of the cold crucible is damaged.

The present invention has been made to solve the above problems,

It is a first object of the present invention to provide an electromagnetic continuous casting apparatus including a cold crucible capable of minimizing damage to the inner surface of the cold crucible while stably continuous casting by limiting the width of the segment to 20 to 50 mm.

It is a second object of the present invention to provide an electromagnetic continuous casting apparatus which minimizes the contact area between molten silicon and the inner surface of the cold crucible to prevent impurities in the cold crucible material component from being contained in the silicon ingot.

It is a third object of the present invention to provide an electromagnetic continuous casting apparatus capable of preventing the silicon ingot from including impurities of a cold crucible material component to suppress a reduction in conversion efficiency of a silicon solar cell.

The fourth object of the present invention is to construct a structure of a conventional lower open type cold crucible into a plurality of assembly (split) types, so that when local damage occurs to the cold crucible, partial repair is possible and the replacement can be facilitated. It is to provide an electromagnetic continuous casting device capable of stable continuous casting.

Electromagnetic continuous casting device according to an embodiment of the present invention,

At least a part of the circumferential direction comprises a conductive open bottom cold crucible disposed in the induction coil in a structure divided into segments by longitudinal slits, and melted by electromagnetic induction heating by the induction coil In the electromagnetic continuous casting device to solidify in the downward direction, the width of the segment is characterized in that 20 to 50mm.

The cross section of the cold crucible may be square or rectangular.

The length of the first edge and the second edge of the cross section of the cold crucible may be 320 to 550 mm.

The length ratio of the first edge and the second edge of the cross section of the cold crucible is preferably 1: 0.6 to 1.7.

The cold crucible may include a plurality of cold crucible parts, and the sides of the cold crucible part may be coupled to each other to form a cold crucible.

Due to the configuration as described above, the electromagnetic continuous casting device according to an embodiment of the present invention has the following effects.

(1) By limiting the width of the segment to 20 to 50mm, it is possible to minimize damage to the inner surface of the cold crucible while stably continuous casting.

(2) The contact area between the molten silicon and the inner surface of the cold crucible can be minimized to prevent the silicon ingot from containing impurities of the cold crucible material component.

(3) It is possible to prevent the silicon ingot from containing impurities of cold crucible material components, thereby reducing the conversion efficiency of the silicon solar cell.

(4) In the case where local damage occurs in the cold crucible by assembling a conventional integrated crucible into a plurality of cold crucible parts, partial repair is possible, replacement is easy, replacement cost is reduced, and stable continuous casting is possible. .

1 is a cross-sectional view showing the configuration of a cold crucible of an electromagnetic continuous casting apparatus according to an embodiment of the present invention.
Fig. 2A is a diagram showing the state of molten silicon due to electromagnetic pressure when the width of the segment is 65 mm.
2 (b) is a diagram showing the state of molten silicon due to electromagnetic pressure when the width of the segment is 20 to 50 mm.
3 is a view showing the damage state of the segments and slits of the cold crucible according to the width of the segment.
4 is a graph showing the life of the cold crucible according to the width of the segment of the cold crucible.
5 is a graph showing the concentration of copper in the wafer of the silicon ingot according to the width of the segment of the cold crucible.
6 is a diagram showing an energy band of silicon.
7 is a graph showing the conversion efficiency and the average carrier life of the solar cell according to the segment width of the cold crucible.
8 is a view showing a cold crucible part in the electromagnetic continuous casting device according to another embodiment of the present invention.
9 is a plan view showing a state in which the cold crucible parts are combined to form a cold crucible in the electromagnetic continuous casting device according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail through exemplary embodiments with reference to the accompanying drawings, and the present invention is not limited thereto. In addition, detailed descriptions of well-known functions and configurations that may blur the gist of the present invention will be omitted.

1 is a cross-sectional view showing the configuration of the cold crucible 100 of the electromagnetic continuous casting device according to an embodiment of the present invention.

The cold crucible 100 is disposed inside the induction coil 130, and has a conductive lower open type that forms a structure in which at least a portion of the circumferential direction is divided into the segments 110 by the slits 120 in the longitudinal direction. The silicon ingot is manufactured by melting silicon by electromagnetic induction heating by the coil 130 and then solidifying it in a downward direction.

The width of the segment 110 of the cold crucible 100 is preferably between 20 and 50 mm.

If the width of the segment 110 is less than 20 mm, it becomes difficult to implement a cooling structure with respect to the segment 110, which makes it difficult to stably solidify the molten silicon 10, and the molten silicon 10 is leaked. do. In addition, since the power must be applied very low to the induction coil 130 for stable solidification of the molten silicon 10, a problem occurs in the continuous silicon melting process.

When the width of the segment 110 exceeds 50 mm, the deviation of the electromagnetic pressure of the molten silicon 10 in the segment 110 and the slit 120 increases, so that the contact area between the inner surface of the cold crucible 100 and the molten silicon 10 is increased. This increases, whereby an alloy is formed between the molten silicon 10 and the material of the cold crucible 100 to severely damage the inner surface of the cold crucible 100.

Example

The cold crucible 100 used oxygen-free copper having excellent electrical conductivity. The width of the segment 110 was manufactured while changing to 18mm, 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, 65mm, and the width of the slit 120 was processed to 0.5mm so that the slit 120 was insulated between the segments 110. 0.3 mm mica plate was inserted. The size of the cold crucible 100 was 345 mm x 345 mm and the length was 550 mm. The induction coil 130 was positioned outside the crucible 100, and a silicon ingot was manufactured while applying up to 700 kW to the coil.

2 (a) is a view showing the state of the molten silicon 10 by the electromagnetic pressure when the width of the segment 110 is 65mm, Figure 2 (b) is 20 to 50mm width of the segment 110 Is a diagram showing a state of the molten silicon 10 due to electromagnetic pressure.

Referring to FIG. 2A, when the width of the segment 110 is 65 mm, the deviation of the electromagnetic pressure with respect to the molten silicon 10 in the segment 110 and the slit 120 is excessive, so that the inner surface of the cold crucible 100 is It can be seen that the area where the molten silicon 10 is in contact with each other increases. Therefore, the frictional force between the molten silicon 10 and the inner surface of the cold crucible 100 is increased in the process of drawing the molten silicon 10 in the downward direction, thereby increasing the damage of the inner surface, and as a result, a smooth continuous casting cannot be achieved. . As a result of confirming the damage degree of the inner surface of the cold crucible 100 after the end of the experiment, it was confirmed that each segment 110 is damaged a lot (see FIG. 3).

Referring to FIG. 2B, when the width of the segment 110 is 20 to 50 mm, the deviation of the electromagnetic pressure with respect to the molten silicon 10 in the segment 110 and the slit 120 is reduced, and thus the molten silicon 10 and It can be seen that the contact area with the inner surface of the cold crucible 100 is almost disappeared. After the experiment, damage to the inner surface of the crucible 100 was also significantly reduced (see FIG. 3).

When the width of the segment 110 is smaller than 20 mm, solidification of the molten metal may not be efficiently performed by the cooling means provided in the segment 110, and the outflow of the molten metal occurs.

4 is a graph showing the life of the cold crucible 100 according to the width of the segment 110 of the cold crucible 100.

As shown in FIG. 4, when the width of the segment 110 is 20 mm to 50 mm, the number of times the use of the cold crucible 100 is 18 to 27 times, while the width of the segment 110 is 65 mm when the width of the segment 110 is 65 mm. It was confirmed that the internal damage was severely reduced to four times.

FIG. 5 is a graph showing the concentration of copper in the wafer of the silicon ingot according to the width of the segment 110 of the cold crucible 100, and FIG. 6 is a diagram showing an energy band of silicon.

As shown in FIG. 5, when the width of the segment 110 is 20 mm to 50 mm, the copper (Cu) concentration in the silicon wafer is contaminated with 185 to 286 ppbw, while when the width of the segment 110 is 65 mm, It was confirmed that the copper (Cu) concentration rapidly increased to about 900ppbw. When the width of the segment 110 is 65 mm, the contact area between the molten silicon and the inner surface of the cold crucible 100 is rapidly increased, and the copper (Cu) concentration in the silicon wafer is rapidly increased. When copper (Cu) is contained in silicon as an impurity, as shown in FIG. 6, it forms an intermediate level of impurity levels in the energy band and acts as a recombination center of electron-hole pairs excited by sunlight. Therefore, the carrier life of the excited electron-hole pairs becomes a factor.

7 is a graph showing the conversion efficiency and the average carrier life of the solar cell according to the width of the segment 110 of the cold crucible 100.

As shown in FIG. 7, when the width of the segment 110 is 20 mm to 50 mm, the conversion efficiency of the silicon solar cell is 15.7 to 15.92%, whereas when the width of the segment 110 is 65 mm, silicon It was confirmed that the conversion efficiency of the solar cell rapidly decreased to 15.17%. In addition, it can be seen that the average carrier life also decreases rapidly when the width of the segment 110 is 65 mm. Therefore, by limiting the width of the segment 110 to 20 to 50mm, it is possible to minimize the decrease in the carrier life of the electron-hole pair excited by sunlight and to suppress the reduction of the solar cell conversion efficiency.

In the electromagnetic continuous casting apparatus according to the embodiment of the present invention, the cross section of the cold crucible 100 may be square or rectangular. The length of the first edge 102 and the second edge 104 of the cross section of the cold crucible 100 is preferably 320 to 550 mm, and the first edge 102 and the second edge of the cross section of the cold crucible 100 ( The length ratio of 104) may be 1: 0.6 to 1.7.

8 is a view showing the cold crucible part 140 in the electromagnetic continuous casting device according to another embodiment of the present invention.

In the electromagnetic continuous casting apparatus according to another embodiment of the present invention, the cold crucible 100 may include a plurality of cold crucible parts 140. The cold crucible parts 140 are preferably the same shape. The cold crucible parts 140 have respective sides 142 (indicated by dashed lines in FIG. 1) joined together to form a cold crucible 100. That is, the plurality of cold crucible parts 140 combine with each other to form an assembled cold crucible 100. By configuring the cold crucible 100 in a divided (assembled) type, it is easy to replace when damage occurs only a part of the cold crucible 100.

9 is a plan view illustrating a state in which the cold crucible parts 140 are combined to form the cold crucible 100 in the electromagnetic continuous casting apparatus according to another embodiment of the present invention.

In FIG. 9, the four cold crucible parts 140 are shown as being combined with each other to form the cold crucible 100, but various numbers of cold crucible parts 140 may be combined.

As mentioned above, although this invention was demonstrated to the said Example, this invention is not limited to this. It will be understood by those skilled in the art that modifications and variations may be made without departing from the spirit and scope of the invention, and that such modifications and variations are also contemplated by the present invention.

10: molten silicon
100: cold crucible
102: corner 1
104: second corner
110: segment
120: slit
130: induction coil
140: cold crucible parts
142: side of the cold crucible part

Claims (5)

At least a part of the circumferential direction comprises a conductive open bottom cold crucible disposed in the induction coil in a structure divided into segments by longitudinal slits, and melted by electromagnetic induction heating by the induction coil In the electromagnetic continuous casting device for solidifying in the downward direction,
Electromagnetic continuous casting device, characterized in that the width of the segment is 20 to 50mm.
The method of claim 1,
Electromagnetic continuous casting device, characterized in that the cross section of the cold crucible is square or rectangular.
The method of claim 2,
Electromagnetic continuous casting apparatus, characterized in that the length of the first edge and the second edge of the cross section of the cold crucible is 320 to 550mm.
The method of claim 2,
Electromagnetic continuous casting apparatus, characterized in that the ratio of the length of the first edge and the second edge of the cross section of the cold crucible is 1: 0.6 to 1.7.
The method of claim 1, wherein the cold crucible is
Including a plurality of cold crucible parts,
Electromagnetic continuous casting device, characterized in that the sides of the cold crucible parts are combined to form a cold crucible.

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