JPH07215714A - Production of polycrystalline silicon and crucible therefor - Google Patents

Abstract

PURPOSE:To provide a process for production of polycrystalline silicon capable of producing a polycrystalline silicon ingot having high quality with high produc tivity at a low cost, and to provide a crucible for production of this polycrystalline silicon. CONSTITUTION:The crucible 10 which has a bottom 10c and an outer peripheral wall 10b enclosing the space above this bottom 10c and has an approximately recessed shape in the section in a perpendicular direction is disposed in a vacuum or inert gas. An inner peripheral wall 10a forming a hole 20 in a perpendicular direction passing approximately passing the center of the crucible 10 is erected to face the outer peripheral wall 10b in the crucible 10. Raw material silicon is melted in the crucible 10 and a cooler is inserted into this hole 20 to solidify the silicon melt 6 from the inner peripheral wall 10b side to the outer peripheral wall 10b side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polycrystalline silicon and a crucible for producing polycrystalline silicon. More specifically, the present invention relates to a method for producing a polycrystalline silicon ingot that is excellent in crystallography, efficiently and at low cost in a short time, and a crucible for producing polycrystalline silicon.

[0002]

2. Description of the Related Art Polycrystalline silicon is suitable as a material for solar cells for electric power from the viewpoint of industrial production and resources, and is in great demand. Recently, as a method for producing a polycrystalline silicon ingot, in a vacuum or in an inert gas, raw silicon is melted in a silica crucible, and the silicon melt is poured into a graphite mold by tilting the crucible. And solidification by a casting method (Japanese Patent Publication No. 57-21515), HEM (heat exchange method) method (Japanese Patent Publication No. 58-54115) in which raw material silicon is melted in a silica crucible and solidified in that state. As a modification of the above, a method of melting the raw material silicon in a steel plate pan (water-cooled hearth) and dropping the silicon melt into a graphite mold provided below to solidify it (JP-A-62-2
No. 60710 gazette) An electromagnetic casting method is known in which molten silicon is confined by an electromagnetic force and a crucible is not used.

According to these methods of melting the raw material silicon in vacuum or in an inert gas, it is possible to prevent oxygen, nitrogen gas and the like from being mixed into the silicon, thereby improving quality and preventing dust.

In the method described above, as shown in FIG. 2 (a), the crucible 100 is attached to the bottom portion 100c and the outer peripheral wall 100.
b is a cylindrical shape (concave cross section), and the crucible 100
Inside, the silicon melt is solidified in one direction from the lower side to the upper side to manufacture the ingot 106I. This is intended to increase the size of crystal grains.

[0005]

However, there is a problem in that it is difficult to increase the productivity and the manufacturing cost is high in the above method. In particular, in the above method, the melting and solidification of the raw material is carried out in a crucible having a cylindrical shape (concave cross section). For example, it takes 4 to 6 hours to solidify 40 kg of raw material silicon. It takes 9 to 12 hours and 10 to 15 hours for cooling for a total of 23 to 33 hours to manufacture one ingot, and the productivity per furnace is extremely poor. Further, in the above method, since the silicon melt is dropped into the mold, the liquid level of the silicon melt greatly fluctuates in the mold, and as a result, the quality of the produced polycrystalline silicon is not good. There is.

Further, in order to improve the productivity, it is preferable to increase the size of the grown ingot. However, in the above method, when the height of the ingot is increased, the crystallinity of the portion (the lower part of the ingot) where the distance from the growth start surface is small decreases as shown by the ● mark in FIG. There is a problem that the conversion efficiency is reduced when a solar cell is manufactured by using the solar cell. This is because the weight of a large amount of silicon melt adversely affects the solidification interface, and strain due to weight remains in the ingot.

Therefore, an object of the present invention is to provide a method for producing polycrystalline silicon and a crucible for producing polycrystalline silicon, which can produce a high-quality polycrystalline silicon ingot with high productivity.

[0008]

In order to achieve the above object, a method for producing polycrystalline silicon according to a first aspect of the present invention is such that an outer circumference surrounding a bottom and a space above the bottom in a vacuum or an inert gas. A crucible having a wall and a vertical cross-section having a substantially concave shape, melting the raw material silicon in the crucible, and solidifying the resulting silicon melt in a polycrystalline silicon manufacturing method, in the crucible, the outer periphery Facing the wall, an inner peripheral wall forming a vertical hole passing through substantially the center of the crucible is erected, a cooling device is inserted into the hole, and the silicon melt is transferred from the inner peripheral wall side to the outer peripheral wall. It is characterized by solidifying toward the side.

The method for producing polycrystalline silicon according to a second aspect is the method for producing a polycrystalline silicon according to the first aspect, wherein the bottom of the crucible is formed so that the hole communicates with a space below the crucible. It is characterized in that the cooling device is penetrated and the cooling device is inserted into the hole from below the crucible.

The method for producing polycrystalline silicon according to claim 3 is the method for producing polycrystalline silicon according to claim 1 or 2, wherein the height of the silicon melt is set to 150 mm or less in the crucible. It is characterized by that.

The crucible for producing polycrystalline silicon according to a fourth aspect of the invention is continuous with a bottom portion having a substantially rectangular plate shape and a peripheral edge of the bottom portion, and surrounds a space above the bottom portion in a frame shape along the peripheral edge. The cooling device is inserted into the hole by including an outer peripheral wall and an inner peripheral wall that is erected in a rectangular frame shape on the bottom so as to face the outer peripheral wall and forms a vertical hole passing through substantially the center of the space. It is characterized by doing so.

[0012]

In the method for producing polycrystalline silicon according to the first aspect, an inner peripheral wall forming a vertical hole passing through substantially the center of the crucible is provided in a crucible having a concave cross section, and a cooling device is inserted into the hole. Then, the silicon melt is solidified from the inner peripheral wall side toward the outer peripheral wall side. As a result, the solidification is performed more quickly than in the conventional method using only a crucible having a concave cross section.
Therefore, the productivity is increased and the cost is reduced. Also,
Since it is solidified in the horizontal direction, the height of the silicon melt in the crucible can be easily suppressed to a certain value or less even when a large-sized silicon ingot is manufactured. This prevents the weight of the silicon melt from adversely affecting the crystallinity of the ingot. As a result, the conversion efficiency when the solar cell is manufactured is improved. Further, since the silicon is melted and solidified in the same crucible, the liquid surface of the silicon melt does not fluctuate and the quality does not deteriorate.

In the method for producing polycrystalline silicon according to claim 2,
Since the hole penetrates the bottom of the crucible so that the hole communicates with the space below the crucible, and the cooling device is inserted into the hole from below the crucible, cooling is easily performed. Therefore, productivity is increased.

In the method for producing polycrystalline silicon according to claim 3,
Since the height of the silicon melt is set to 150 mm or less in the crucible, the weight of the silicon melt does not adversely affect the crystal quality of the ingot. As a result,
The conversion efficiency when producing a solar cell is improved.

According to the crucible for producing polycrystalline silicon of claim 4, a cooling device can be inserted into the hole formed by the inner peripheral wall to solidify the silicon melt from the inner peripheral wall side toward the outer peripheral wall side. . Therefore, the solidification is performed more quickly than in the conventional case. Therefore, the productivity is increased and the cost is reduced. Further, since it is solidified in the horizontal direction, the height of the silicon melt in the crucible can be easily suppressed to a certain value or less even when a large-sized silicon ingot is manufactured. This prevents the weight of the silicon melt from adversely affecting the crystallinity of the ingot. As a result, the conversion efficiency when the solar cell is manufactured is improved.
Further, since the silicon can be melted and solidified in the same crucible, the liquid surface of the silicon melt does not fluctuate and the quality does not deteriorate. Moreover, since the outer peripheral wall and the inner peripheral wall of this crucible are formed in a rectangular frame shape, the ingot is finished in a square shape when viewed from above. When a rectangular solar cell is mass-produced, for example, the ingot may be sliced in the horizontal direction and the wafer may be cut out from each side of the square shape. When cutting a wafer from an ingot having such a linear outer shape, compared to cutting a wafer from a columnar ingot, waste (cutting margin) associated with cutting the wafer
Is less. Therefore, the cost for manufacturing the solar cell is reduced.

[0016]

EXAMPLES The method for producing polycrystalline silicon and the crucible for producing polycrystalline silicon according to the present invention will be described in detail below with reference to examples.

FIG. 1 (a) shows an apparatus for producing a polycrystalline silicon ingot according to the present invention. This apparatus comprises a closed container 2 which is evacuated by a vacuum pump. On both sides of the closed container 2, crucible take-out chambers 15a and 15b are provided. The inside of the closed container 2 and the crucible take-out chambers 15a and 15b are connected to the shaft 14a,
It is partitioned by vacuum shut-off doors 9a and 9b which are opened and closed by 14b. 8 is a cart for moving the crucible, and 16 is a rail.

An induction heating furnace (frequency: 10 KHz) 7 as a heating means is provided inside the closed container 2. The induction heating furnace 7 has a cylindrical shape extending in the vertical direction and contains a water-cooled copper coil. A heat insulating wall 4 is provided on the outer periphery thereof.

In the induction heating furnace 7, there is provided a crucible 10 having a substantially concave vertical cross section (the crucible 10).
Are removed when the equipment is not in operation. ). As shown in FIG. 1B, the crucible 10 has a bottom portion 10
c, an outer peripheral wall 10b, and an inner peripheral wall 10a. The bottom portion 10c has a rectangular plate shape with a size of 60 cm × 60 cm, and a rectangular through hole with a size of 10 cm × 10 cm (see FIG. 7A) is provided in the center. The outer peripheral wall 10b surrounds the space above the bottom 10c in a frame shape along the peripheral edge of the bottom 10c. The height of the outer peripheral wall 10b is 20 cm. Inner wall 10a
Is erected in a rectangular frame shape at the edge of the through hole of the bottom portion 10c so as to face the outer peripheral wall 10b. The inner peripheral wall 10a forms a vertical hole 20 that passes through substantially the center of the crucible. The bottom portion 10c, the outer peripheral wall 10b, and the inner peripheral wall 10a of the crucible 10 are mainly made of high-purity silica having a thickness of about 1 cm. A silicon nitride layer is applied to the surface of the crucible 10 that is in contact with the silicon melt 6 by a general method such as spraying or brush coating. This silicon nitride layer suppresses the reaction with silicon.

As shown in FIG. 1 (a), the crucible 10 is
It is supported from below by a crucible supporting device 13 as a supporting means via a heat insulating material 17. The supporting device 13
Can move up and down the crucible 10 at a set speed.

During operation, the hole 20 of the crucible 10 is
A cooling water pipe 5 as a cooling device is inserted from below to the inside. The cooling water pipe 5 is composed of a forward path portion extending upward along the support device 13 and a return path portion which is inverted at the top and extends downward, and the cooling water is flowed from the forward path portion to the return path portion.

Using this apparatus, a polycrystalline silicon ingot is manufactured by the work procedure described below. It is assumed that the closed container 2 is in a vacuum state in advance.

A chip or block-shaped raw material silicon 6 is supplied into the crucible 10 outside the closed container 2. At this time, the supply amount is set so that the height of the melted silicon melt surface 6s (from the crucible bottom portion 10c) is 150 mm or less. Since the height of the silicon melt surface 6s is set to 150 mm or less, it is possible to prevent the weight of the silicon melt 6 from adversely affecting the crystallinity of the solidified polycrystalline silicon. As a result, as will be described later, it is possible to improve the conversion efficiency when manufacturing a solar cell. In actuality, considering the productivity, the height of the silicon melt 6 is 100.
Set within the range of ~ 150mm.

For example, in the figure, the crucible 10 is put in the crucible take-out chamber 15a on the right side and the chamber 15a is evacuated. Subsequently, the vacuum shut-off door 9a is temporarily opened, and the crucible 10 placed on the carriage 8 is inserted into the vacuum container 2 from the crucible take-out chamber 15a and moved to the position of the crucible support device 13. Then, the crucible supporting device 13 is driven to raise the crucible 10 to the height of the center of the induction heating furnace 7.

The induction heating furnace 7 is energized to heat the temperature of the crucible 10 to a temperature higher than the melting point of silicon (1410 ° C.) to once melt the raw material silicon. After that, the temperature of the crucible 10 is set to 10 ° C higher than the melting point of silicon (1410 ° C).
The temperature is set to a low temperature of about 0 to 200 ° C.

Wait until the temperature of the crucible 10 stabilizes, and confirm that the temperature has reached a predetermined temperature and a predetermined position for solidification.
The cooling water pipe 5 is inserted into the hole 20 of the crucible 10 from below. By this cooling pipe 5, the silicon melt 6 is forcibly cooled, and the silicon melt is solidified from the inner peripheral wall 10a side to the outer peripheral wall 10b side as shown in FIG. 2 (b). As a result, a polycrystalline silicon ingot 6I is obtained. Actually manufactured polycrystalline silicon ingot 6I
The unidirectional growth was complete from the inner peripheral wall 10a side to the outer peripheral wall 10b side.

The temperature of the crucible 10 shown in FIG.
When the temperature drops to ℃, the crucible 10 is placed on the carriage 8 and moved to the crucible take-out chamber 15a. After waiting for the temperature of the crucible 10 to fall to 400 ° C. or lower, the crucible take-out chamber 1
Take out to the outside of 5a. The temperature of the crucible 10 is 730
When the polycrystalline silicon ingot is moved at a temperature higher than ° C, crystal defects such as cracks occur in the polycrystalline silicon ingot, and the quality is deteriorated. On the other hand, when it is moved at a temperature lower than 730 ° C., the solidification time becomes long and the productivity decreases.

When manufacturing a polycrystalline silicon ingot continuously, another crucible is inserted into the vacuum container 2 from the crucible take-out chamber 15b on the opposite side at the same time as the process. Then, the work from step to is repeated.

As described above, in this manufacturing method, since the cooling water pipe 5 is inserted into the hole 20 of the crucible 10 to solidify the silicon melt from the inner peripheral wall 10a side to the outer peripheral wall 10b side, the sectional shape is simply concave. As compared with the conventional method using the crucible, the solidification can be performed more quickly. Therefore, the productivity is improved, and the polycrystalline silicon ingot 6 is manufactured at low cost.
I can be produced. Actually, the time required to manufacture about 40 kg of the polycrystalline silicon ingot 6I was about 10 hours, which was significantly shorter than the conventional time.

The surface 6 of the silicon melt in the crucible 10
Since the height of s is set to 150 mm or less, the adverse effect of the weight of the silicon melt 6 is eliminated, and the ingot 6I
The crystallinity of can be improved. As a result, it is possible to improve the conversion efficiency when the solar cell is manufactured.
Further, since the silicon is melted and solidified in the same crucible 10, the silicon melt surface 6s does not fluctuate, and it is possible to prevent quality deterioration due to liquid level fluctuation. Actually, a 10 cm square wafer was cut out from each of the inner peripheral wall 10a side, the outer peripheral wall 10b side, and the central portion between the inner peripheral wall and the outer peripheral wall in the vicinity of the bottom of the manufactured polycrystalline silicon ingot 6I to obtain a wafer with a lifetime of 10 cm. Was measured and found to be 5 to 10 μsec as shown in “Table 1”. Also,
When a solar cell was prototyped by a known standard process,
The conversion efficiency was 14.4 to 15% (the result of this conversion efficiency is shown by a circle in FIG. 3). These are properties comparable to those reported in the past. Further, it can be said that there is little characteristic variation in the ingot 6I and the characteristic stability is excellent.

[Table 1] Further, in this example, the outer peripheral wall 10b and the inner peripheral wall 10 of the crucible 10 are
Since a is formed in a rectangular frame shape, the ingot 6
I is finished in a square shape when viewed from above. Therefore, for example, when mass-producing a rectangular solar cell having a size of 10 cm square, for example, the ingot 6I may be sliced in the horizontal direction and the wafer may be cut out from each side of the square shape. When the wafer is cut out from the ingot having such a linear outer shape, waste (cutting margin) associated with cutting out the wafer can be reduced as compared with the case where the wafer is cut out from the columnar ingot. Therefore, the solar cell can be manufactured at low cost.

[0031]

As is clear from the above, the method for producing polycrystalline silicon according to the first aspect of the present invention is characterized in that a crucible having a concave cross section is provided with:
An inner peripheral wall forming a vertical hole passing through substantially the center of this crucible is erected, and a cooling device is inserted into the hole to solidify the silicon melt from the inner peripheral wall side toward the outer peripheral wall side. Therefore, as compared with the conventional method in which a crucible having a concave cross section is simply used, the solidification can be performed quickly. Therefore, it is possible to increase productivity and manufacture polycrystalline silicon at low cost. Further, since it is solidified in the horizontal direction, the height of the silicon melt in the crucible can be easily suppressed to a certain value or less even when a large-sized silicon ingot is manufactured. This can improve the crystallinity of the ingot by eliminating the adverse effect of the weight of the silicon melt. As a result, it is possible to improve the conversion efficiency when the solar cell is manufactured. Further, since the silicon is melted and solidified in the same crucible, the surface of the silicon melt can be prevented from fluctuating, and the quality deterioration due to the fluctuation of the liquid surface can be prevented.

In the method for producing polycrystalline silicon according to claim 2,
Since the hole penetrates the bottom of the crucible so that the hole communicates with the space below the crucible, and the cooling device is inserted into the hole from below the crucible, cooling can be easily performed. Therefore, productivity can be increased.

In the polycrystalline silicon manufacturing method according to claim 3,
Since the height of the silicon melt in the crucible is set to 150 mm or less, the crystallinity of the ingot can be improved by eliminating the adverse effect of the weight of the silicon melt. As a result, it is possible to improve the conversion efficiency when the solar cell is manufactured.

According to the crucible for producing polycrystalline silicon of claim 4, a cooling device can be inserted into the hole formed by the inner peripheral wall to solidify the silicon melt from the inner peripheral wall side toward the outer peripheral wall side. . Therefore, solidification can be performed more quickly than in the conventional case. Therefore, it is possible to increase productivity and manufacture polycrystalline silicon at low cost. Further, since it is solidified in the horizontal direction, the height of the silicon melt in the crucible can be easily suppressed to a certain value or less even when a large-sized silicon ingot is manufactured.
This can improve the crystallinity of the ingot by eliminating the adverse effect of the weight of the silicon melt. As a result, it is possible to improve the conversion efficiency when the solar cell is manufactured. Further, since the silicon is melted and solidified in the same crucible, the surface of the silicon melt can be prevented from fluctuating, and the quality deterioration due to the fluctuation of the liquid surface can be prevented. Moreover, since the outer peripheral wall and the inner peripheral wall of this crucible are formed in a rectangular frame shape, the ingot is finished in a square shape when viewed from above. When a rectangular solar cell is mass-produced, for example, the ingot may be sliced in the horizontal direction and the wafer may be cut out from each side of the square shape. When cutting a wafer from an ingot having a linear outer shape as described above, it is possible to reduce waste (cutting margin) associated with cutting a wafer, as compared with cutting a wafer from a cylindrical ingot. Therefore, the cost for manufacturing a solar cell can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an apparatus for producing a polycrystalline silicon ingot according to the present invention.

FIG. 2 is a diagram showing a crystal growth direction in a crucible.

FIG. 3 is a diagram showing conversion efficiency of a solar cell using polycrystalline silicon manufactured by the present invention as a material.

[Explanation of symbols]

 2 vacuum container 5 cooling water pipe 6 silicon melt 6I polycrystalline silicon ingot 7 induction heating furnace 10 crucible 20 holes

Claims (4)

[Claims] 1. A bottom portion in vacuum or in an inert gas,
With a peripheral wall that surrounds the space on the bottom, a crucible with a vertical cross section having a substantially concave shape is provided, the raw material silicon is melted in the crucible, and the resulting silicon melt is solidified in a polycrystalline silicon manufacturing method. , Inside the crucible, facing the outer peripheral wall, standing up an inner peripheral wall forming a vertical hole passing through substantially the center of the crucible, insert a cooling device in the hole, the silicon melt A method for producing polycrystalline silicon, characterized by solidifying from the inner peripheral wall side toward the outer peripheral wall side. 2. The method for producing polycrystalline silicon according to claim 1, wherein the hole penetrates a bottom portion of the crucible so that the hole communicates with a space below the crucible, and the cooling device is provided from below the crucible. A method for producing polycrystalline silicon, characterized by inserting into a hole. 3. The method for producing polycrystalline silicon according to claim 1 or 2, wherein the height of the silicon melt in the crucible is set to 150 mm or less. 4. A bottom having a substantially rectangular plate shape, an outer peripheral wall continuous with a peripheral edge of the bottom and surrounding a space on the bottom in a frame shape along the peripheral edge, and the bottom facing the outer peripheral wall. Polycrystalline silicon manufacturing characterized in that it is provided upright in a rectangular frame shape and has an inner peripheral wall forming a vertical hole passing through substantially the center of the space, and a cooling device is inserted into the hole. A crucible.