JPH08283095A - Production of silicon crystal plate - Google Patents

Abstract

PURPOSE: To obtain a process for producing a silicon crystal plate capable of lessening the inclusion of impurities in this crystal plate, decreasing the energy required for melting a silicon raw material, continuously and stably producing the smooth silicon plate crystal and shortening the time before the start of production. CONSTITUTION: A long-sized woven textile-like base material 1 consisting of a fibrous material which is, for example, carbon fiber woven fabric and has high heat resistance is sent in the direction of an arrow A from a roll 2. The silicon raw material 5 ground to a powder form is supplied from a powder supplying device 6 onto the base material 1 and is then sent to a melting furnace 7. The base material 1 and the silicon raw material 5 are heated by using an IR radiation lamp 8 which is a lamp heater and a condensing mirror 9 from the outside of a melting furnace 7 in this furnace, by which the silicon raw material is melted and is extremely rapidly penetrated between the carbon fibers of the base material 1. In addition, the surface of the base material 1 is covered with this melt. In succession, the molten silicon is cooled down to the m. p. of the silicon or below and is solidified, by which the silicon crystal plate 12 consisting of polycrystalline silicon is obtd.

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 a crystalline substrate made of silicon, and more particularly to a method for producing a crystalline plate material by remelting silicon as a raw material. .

[0002]

2. Description of the Related Art Various methods using a silicon melt have been proposed as a method for forming a polycrystalline silicon substrate used for manufacturing a solar cell or the like.

As an example, for example, J. of Crystal Gr
owth (Journal of Crystal Grouse), 82
(1987), p10. In this method, the raw material silicon is melted in the crucible, and a long net made of carbon fibers is continuously supplied to the surface of the melt, and silicon is provided between the meshes of the carbon fibers by bringing them into contact with each other. This is a method for producing a polycrystalline silicon plate by forming a liquid film and cooling and solidifying it.

In this prior art, a carbon fiber net is used as a base material for producing a polycrystalline plate, but as a method without using a base material, for example, J. of Crystal Growth, 50 (1980), p2.
There is a method announced in 47. In this method, a wide plate-shaped seed crystal is brought into contact with a melt of silicon melted in a crucible, and is pulled out in one direction to continuously produce a band-shaped crystal plate.

By using these conventional techniques, it is possible to continuously manufacture a long crystal plate of polycrystalline silicon suitable for manufacturing a solar cell.

[0006]

However, these techniques have the following many problems. 1. Silicon has a very high melting point of 1414 ° C, and if these high-melting-point materials are melted using a crucible, the crucible material mixes into the melt, and the serious problem of decreasing the purity of the crystal plate produced is a serious problem. there were.

2. In any of the above-mentioned conventional techniques, since the crystal plate is formed by the liquid surface of the melt in the crucible, undulation occurs on the surface of the crystal plate formed when disturbance such as waves occurs on the surface of the melt, Alternatively, the crystal plate may be interrupted, making it impossible to manufacture the crystal plate itself. Further, keeping the melt surface at a constant height is also important for producing a good crystal plate. On the other hand, in order to continuously manufacture a crystal plate, a solid material of silicon, which is a raw material, must be continuously supplied and melted. However, it is difficult to continuously supply the solid material into the crucible without disturbing the melt surface, which causes the above trouble.

3. In the prior art, since the crystal plate is formed by the liquid surface of the silicon melt in the crucible, it is the silicon material that stays in the vicinity of the liquid surface of the melt that is consumed at that time. Since it is necessary to melt all the solid raw materials existing below the vicinity of the liquid surface of the melt inside,
It requires a large amount of power. Therefore, the manufacturing equipment becomes large-scale and the manufacturing cost becomes high.

4. Since it takes a long time to melt all the solid raw materials in the crucible, it takes a long time to start the production. 5. The crucible is a consumable item (depending on the material that constitutes the crucible, it is gradually dissolved in the silicon melt and lost, or is consumed by being sublimated by high-temperature heating or being oxidized). Will be higher.

The present invention solves the problems of the conventional method, less impurities are mixed, the energy (power consumption) required for melting the silicon raw material is reduced, and a smooth silicon plate crystal is continuously formed. It is an object of the present invention to provide a method for manufacturing a silicon crystal plate, which can be stably manufactured in a stable manner and can shorten the time required to start the manufacturing.

[0011]

In order to solve the above-mentioned problems, a method for producing a silicon crystal plate according to the present invention comprises a long woven fabric-like base material made of a fibrous material having high heat resistance in the longitudinal direction. While moving, a granular or powdery silicon raw material was supplied onto the base material, and the silicon raw material on the base material was heated and melted by a heating means arranged in a non-contact position with the silicon raw material and the base material. It is characterized by being post-cooled and solidified.

In the method for producing a silicon crystal plate of the present invention, the base material is a woven fabric made of carbon fibers, a woven fabric made of quartz fibers, or a woven fabric made of carbon fibers and quartz fibers. Is preferred.

In the method for producing a silicon crystal plate according to the present invention, the heating means is preferably a lamp heater or an induction heating heater. Further, in the above-described method for producing a silicon crystal plate of the present invention, it is preferable that the atmosphere for heating and melting the silicon raw material is an atmosphere containing hydrogen gas.

Further, the method for producing a silicon crystal plate of the present invention preferably has a step of irradiating the surface of the base material with a flame before supplying the silicon raw material onto the base material.

[0015]

The method for producing a silicon crystal plate according to the present invention comprises a long woven fabric base material made of a fibrous material having high heat resistance, which is moved in the lengthwise direction while being granular or powdery on the base material. A silicon-like raw material is supplied, and the silicon raw material on the base material is heated and melted by a heating means arranged in a non-contact position with the silicon raw material and the base material, and then cooled and solidified. The amount of the silicon raw material supplied above is only the amount necessary for forming the silicon crystal plate. Therefore, the amount of silicon that needs to be melted is the minimum amount necessary to form a crystal plate of a target thickness, that is, the granular or powdery silicon raw material supplied on the substrate, and therefore the minimum amount. A crystal plate can be manufactured with a limited melting energy. Therefore, in the case of the conventional method of melting a silicon raw material in a crucible or the like, a considerably large amount of extra silicon raw material must be melted in the crucible at the same time as described above. You can save a lot of energy. In addition, since a woven fabric made of a fibrous material is used as the base material, the molten silicon is quickly penetrated between the fibers due to the surface tension, so that a crystal plate having a uniform thickness can be manufactured quickly. . Moreover,
Since the silicon raw material is melted by heating it with a heating means arranged in a non-contact position with the silicon raw material and the base material, the silicon raw material can be melted without touching a heating device such as a crucible. Does not decrease, and the mixing of impurities can be reduced.

In the method for producing a silicon crystal plate of the present invention, the base material is a woven fabric made of carbon fiber, a woven fabric made of quartz fiber, or a woven fabric made of carbon fiber and quartz fiber. By using these woven fabrics, they are relatively easily industrially available among woven fabrics with high heat resistance, retain the strength required for processing, and melted silicon adheres and solidifies. It has heat resistance to withstand the heat history up to and is preferable because it does not adversely affect the characteristics of the obtained silicon crystal plate.

Further, in the method for producing a silicon crystal plate of the present invention, when a lamp heater or an induction heater is used as the heating means, the apparatus is not large in size and simple, and the high temperature can be relatively easily achieved. Since this can be achieved and efficient heating can be achieved, energy loss is small and power consumption can be reduced. Moreover, these heating means can naturally melt the silicon raw material without touching the heating device such as the crucible, so that the purity of the crystal plate to be produced does not deteriorate.

Further, in the method for producing a silicon crystal plate of the present invention, hydrogen gas is caused to exist in the atmosphere when the silicon raw material is heated and melted, so that dangling bonds existing at the crystal grain boundaries are changed by hydrogen. It is possible to terminate and improve the quality of the obtained silicon polycrystalline plate.
In addition, the silicon raw material is usually stored so as not to come into contact with the atmosphere, and is handled in an atmosphere of an inert gas such as Alcon gas.Since the raw material silicon is a powder, it has a large specific surface area and oxygen in the air. It is easy to adsorb etc. Therefore, when the silicon raw material is melted, there is a problem that oxygen adsorbed on the surface is taken into the produced crystal plate. However, due to the presence of hydrogen gas in the heating and melting atmosphere, oxygen is removed during melting, and a good-quality silicon crystal plate can be manufactured.

Further, in the present invention, since the woven substrate made of the fibrous material is used, if there is a fiber which is frayed and protruded on the surface of the substrate, the fiber penetrates through the formed crystal plate. It may end up. In particular, when using a substrate made of carbon fiber woven fabric, since carbon fiber is a conductor, the presence of such carbon fiber causes further defects in electronic devices such as solar cells formed using a crystal plate. The problem of easily occurring is preferable because irradiation of a flame on the surface of the base material before burning the silicon raw material onto the base material can remove such frayed fibers by burning or melting.

[0020]

Examples As the fibrous material having high heat resistance which constitutes the woven base material in the present invention, granular or powdery silicon raw material supplied on the base material is melted and adhered to the base material to be solidified. A fibrous material that has heat resistance to the extent that at least it does not occur that the base material melts or sublimes to open holes in the heat history until As long as it is a material, it can be obtained relatively easily industrially, and it retains the strength required for processing.
Since it has heat resistance to withstand the above heat history and does not adversely affect the characteristics of the obtained silicon crystal plate, it is usually a woven fabric made of carbon fiber, a woven fabric made of quartz fiber, or a carbon fiber and quartz fiber. It is preferable to use a fabric selected from the fabrics consisting of

The thickness of the base material is not particularly limited, since it varies considerably depending on the intended use of the silicon crystal plate, but a thickness of, for example, about 100 to 600 μm is used when the obtained silicon crystal plate is handled. It is preferably used because it is not easily broken by physical stress, and it is not uneconomical because it is too thick.

The granular or powdery silicon raw material to be supplied onto the base material may be any granular or powdery silicon raw material having a size not to fall from between the eyes of the base fabric, The average particle diameter is preferably about 0.1 to 5 mm, although not particularly limited. If the particle size is too large, it will take a long time to melt or require a considerably large amount of heat energy,
Accordingly, it is necessary to use a heating means having a large power.

The supply amount of the silicon raw material also depends on the thickness of the intended silicon crystal plate, and is not particularly limited, but at least when the silicon raw material is melted and solidified, the surface of the woven substrate is covered. It suffices to supply an amount equal to or larger than the above amount. The thickness of the silicon crystal plate obtained by the method of the present invention varies depending on the intended use of the silicon crystal plate and so is not particularly limited, but is usually about 200 μm to 1 mm. In that case, it is not easily broken by physical stress, and it is not uneconomical because it is too thick, so that it is preferably used.

The heating atmosphere for heating and melting the silicon raw material is usually an inert gas atmosphere such as argon gas. Further, for example, by mixing hydrogen gas of about 0.1 to 10% by volume, It is possible to terminate the dangling bonds existing at the grain boundaries with hydrogen to improve the quality of the obtained silicon polycrystalline plate, and because the oxygen adsorbed in the raw material is removed during melting, a good quality silicon crystalline plate Is also preferable because it can be produced.

A specific embodiment of the method for producing a polycrystalline silicon plate according to the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 shows an overall view of a manufacturing process of a silicon polycrystalline plate of the present invention. In FIG. 1, reference numeral 1 denotes a long base material made of a carbon fiber woven fabric, which is wound around a roll 2 in a roll shape and is rewound from this state and supplied. The structure of the base material 1 is, for example, as shown in FIG. 2, formed by weaving a carbon fiber bundle 4 in which 1000 carbon fibers 3 each having a diameter of 7 μm are bundled in a vertical and horizontal direction.

The base material 1 is sent in the direction of arrow A in FIG. 1, and a silicon material 5 crushed into powder is supplied to the melting furnace 7 by a predetermined amount from a powder supply device 6. . As for the part of the melting furnace 7, as shown in a cross-sectional view by enlarging it in detail in FIG. 3, an infrared radiation lamp 8 as a lamp heater and a condenser mirror 9 are used from the outside to place the substrate in a quartz container 10. The material 1 and the silicon raw material 5 are heated. The infrared radiation lamp 8 has an elongated shape having a length in a direction perpendicular to the plane of the drawing, and the condensing mirror 9 causes the infrared radiation 11 emitted from the infrared radiation lamp 8 to reach the area B in the drawing to the width of the substrate 1. It is designed to have a long focal point across the direction. In this way, by using the infrared radiation lamp 8 and the condenser mirror 9 as a heating source to focus,
A high temperature can be obtained in the focal area B even with low power consumption.
The silicon heated in the focal area B melts and becomes a melt.
On the other hand, since the base material 1 is also heated from the lower surface, the base material 1
It itself is heated to a temperature higher than the melting point of silicon. Therefore, the melt of the melted silicon is the carbon fiber 3 of the base material 1.
Permeates very quickly between them to form a liquid film covering the base material 1. Moreover, the liquid film forms an extremely flat surface due to the surface tension. Since the base material 1 is moving in the direction of the arrow A in the figure, the surface is covered with the liquid film, then comes off the focal region B, and is cooled and solidified to become a polycrystalline silicon plate. As shown in the sectional view of FIG. 4, the solidified silicon completely covers the carbon fiber bundles 4 constituting the base material 1 and has a flat surface with the same shape as that of the melt. It becomes the silicon crystal plate 12 made of silicon.

The amount of the silicon raw material 5 supplied onto the base material 1 is set to an optimum amount so that the melt covers the carbon fiber bundles 4 and forms the silicon crystal plate 12 having a desired thickness. Has been done. In other words, this amount is the minimum amount necessary to form the silicon crystal plate 12 having the target thickness.
On the other hand, in the conventional technique, since silicon as a raw material is melted in the crucible, it is necessary to melt a large excess of the raw material, which is more than the amount necessary for forming the target thickness of the silicon crystal plate having the target thickness. The technique of the present invention has an important feature that the amount of energy required for melting is small because the amount of silicon raw material to be melted is smaller than that of the conventional technique. Further, since the melting amount is small, the silicon crystal plate 12 can be manufactured immediately after starting the apparatus.

In the present invention, since the woven fabric-like substrate 1 in which the fibers are woven is used, the melt permeates between the fibers of the substrate 1 and spreads quickly. Moreover, the surface of the melt that has penetrated is automatically flat due to the surface tension and the thickness becomes uniform. In the present invention, the melt thus formed is solidified to produce a crystal plate, so that a silicon crystal plate having a smooth surface and a uniform thickness can be produced stably and at a high speed.

The melting furnace 7 is supplied with an argon gas 13 mixed with hydrogen gas of about 0.1% to 10%. Argon gas is supplied to prevent oxidation of molten silicon, and hydrogen gas terminates dangling bonds existing at grain boundaries with hydrogen,
It is added to improve the quality of the polycrystalline plate. In addition, 13 'in the figure has shown the gas discharge path. The silicon raw material 5 is stored so as not to come into contact with the atmosphere, and the powder supply device 6 is also filled with an inert gas. However, since the silicon that is the raw material is powder, it has a large specific surface area. Easy to adsorb oxygen etc. Therefore, when the silicon raw material is melted, there is a problem that oxygen adsorbed on the surface is taken into the produced crystal plate. However, when hydrogen gas is supplied to the melting furnace 7 as in the present invention, oxygen is removed during melting and a high-quality silicon crystal plate can be manufactured.

The carbon fibers 3 constituting the substrate 1 supplied by the roll 2 shown in FIG. 1 are each one continuous filament. By the way, although the carbon fiber has a strong resistance to the tensile force in the length direction, it has a drawback that it is easily broken when a force of bending at an acute angle or a force of rubbing the surface acts. Therefore, when the surfaces of the fabric, which is the base material, rub against each other during transportation on the roll 2 or attachment, the surface of the base material 1 is damaged, and the fibers are torn to cause fraying. When a polycrystalline plate is formed using the base material 1 in which such damage or fraying has occurred, the fiber ends 23 resulting from fraying as shown in FIG. 5 are taken into the silicon crystal plate 12, Alternatively, there is a problem that the fiber ends 24 project from the silicon crystal plate 12. Since carbon fiber is a conductor,
The presence of such fiber penetration causes defects in the device formed on the surface of the silicon crystal plate 12. Therefore, in the present invention, in order to remove the frayed fibers, the base material 1 is irradiated with the flame 16 that burns, for example, high-purity oxygen gas and methane gas by the burner 15 shown in FIG. Have been removed. Even when the base material 1 is irradiated with the flame 16 in this manner, the base material 1 itself has a large heat capacity as compared with the frayed fibers, so that the base material 1 is not damaged.

Although not shown in FIG. 1, a suction unit for removing deposits adhering to the substrate 1 between the roll 2 and the irradiation unit of the flame 16 and a unit for spraying clean compressed air. Is provided.

[Embodiment 2] A second embodiment of the present invention is shown in FIG.
Will be explained. FIG. 6 is a sectional view showing the melting furnace portion of the second embodiment, and the other portions are the same as those shown in FIG.

In this embodiment, the heating source has a frequency of 1 MHz.
An induction heating device using a high frequency power source 17 of z and an induction coil 18 is used. In this method, first, the base material 1 made of carbon fiber, which is a conductor, is heated by high-frequency power, and the silicon raw material 5 is heated to a temperature at which it becomes a conductor by conduction of the heat. The silicon raw material 5 that has become a conductor absorbs high-frequency power and further rises in temperature to melt. Also in this method, the silicon raw material 5 can be efficiently melted without being contaminated, and a polycrystalline silicon plate can be manufactured.

Although carbon fibers were used as the material of the base material 1 in the above-mentioned examples, the present invention is characterized in that a long woven base material made of a fibrous material having high heat resistance is used. The fiber material of the material may be quartz fiber or a composite base material of carbon fiber and quartz fiber. In particular, as described above, carbon fibers are easily broken when bent at an acute angle, so long-length fibers, that is, a composite fabric using warp as carbon fiber and quartz fiber as weft, has the above-mentioned frayed fibers. It is excellent as a substrate because it is less likely to cause defects. In addition, it is also preferable to use a carbon fiber woven fabric in which the ends of a woven fabric-like base material are fixed so as not to be disturbed by using quartz fibers.

In this embodiment, a plain weave base material composed of warp threads and weft threads was used, but the present invention does not limit the weaving method of the base material at all, and a woven base material having another woven structure is used. It can also be used. The spacing between the fiber bundles may be such that the powdery or granular silicon raw material to be supplied does not drop and the melt quickly permeates to form a liquid film.

[0036]

According to the present invention, the silicon raw material on the base material is heated and melted by the heating means arranged in a non-contact position with the silicon raw material and the base material, so that it can be melted without using the crucible. It is possible to solve the problem that the purity of the crystal plate produced by mixing the crucible material into the silicon melt is reduced, and the cost required for the consumable crucible does not occur. Moreover, since the supply of solid silicon as a raw material is easy and stable, a smooth plate crystal can be stably produced.

Further, in the technique of the present invention, the amount of silicon to be melted is the minimum amount necessary to form a silicon crystal plate, so that the power consumption is extremely higher than that in the conventional method of melting all solid raw materials in the crucible. It is small, and the time required to melt the raw materials and start the production can be greatly shortened.

In the method for producing a silicon crystal plate of the present invention, the base material is a woven fabric made of carbon fiber, a woven fabric made of quartz fiber, or a woven fabric made of carbon fiber and quartz fiber. According to the preferred embodiment used,
These fabrics are relatively industrially easily available among the heat-resistant fabrics, retain the strength required for processing, and heat until the molten silicon adheres and solidifies. It has heat resistance to withstand history and does not adversely affect the characteristics of the obtained silicon crystal plate, which is preferable.

Further, in the method for producing a silicon crystal plate according to the present invention, according to a preferred embodiment of the present invention in which a lamp heater or an induction heating heater is used as a heating means, the heating device is not large and simple, and comparison is made. Since high temperature can be achieved easily and heating can be performed efficiently, energy loss is small and power consumption can be reduced.

In the method for producing a silicon crystal plate of the present invention, hydrogen gas is allowed to exist in the atmosphere when the silicon raw material is heated and melted. The resulting dangling bond can be terminated with hydrogen to improve the quality of the obtained silicon crystal plate. Also, in the heating and melting atmosphere,
Owing to the presence of hydrogen gas, oxygen adsorbed on the raw material at the time of melting is removed, and a high-quality silicon crystal plate can be manufactured.

In the method for producing a silicon crystal plate of the present invention, a preferred embodiment of the present invention further comprising a step of irradiating a flame on the surface of the base material before supplying the silicon raw material onto the base material. By irradiating the surface of the base material with a flame, the fibrous material is frayed and the fibers protruding to the surface of the base material can be burned or melted to be removed. A method for manufacturing a plate can be provided.

[Brief description of drawings]

FIG. 1 is an overall view showing a manufacturing process of a silicon crystal plate according to a first embodiment of the present invention.

FIG. 2 is a surface view of a base material used in an example of the present invention.

FIG. 3 is a partial cross-sectional view near the melting furnace used in the first embodiment of the present invention.

FIG. 4 is a cross-sectional view of a silicon crystal plate obtained by the method of the present invention.

FIG. 5 is a cross-sectional view of a silicon crystal plate in the case where a fiber end that is a fray of a base fiber is present in a base material.

FIG. 6 is a partial sectional view of the vicinity of a melting furnace used in a second embodiment of the present invention.

[Explanation of symbols]

 1 Base Material 3 Carbon Fiber 4 Carbon Fiber Bundle 5 Silicon Raw Material 6 Powder Feeding Device 7 Melting Furnace 8 Infrared Radiation Lamp 9 Condensing Mirror 12 Silicon Crystal Plate 13 Argon Gas with Hydrogen 15 Burner 16 Flame 17 High Frequency Power 18 Induction Coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Munehiro Shibuya 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A granular or powdery silicon raw material is supplied onto the base material while moving a long woven base material made of a fibrous material having high heat resistance in the lengthwise direction, A method for producing a silicon crystal plate, comprising: heating a silicon raw material on a base material by a heating means arranged at a position not in contact with the silicon raw material and the base material to melt and then solidify by cooling. 2. The method for producing a silicon crystal plate according to claim 1, wherein the substrate is a woven fabric made of carbon fibers, a woven fabric made of quartz fibers, or a woven fabric made of carbon fibers and quartz fibers. . 3. The method for producing a silicon crystal plate according to claim 1, wherein the heating means is a lamp heater or an induction heater. 4. The method for producing a silicon crystal plate according to claim 1, wherein the atmosphere for heating and melting the silicon raw material is an atmosphere containing hydrogen gas. 5. Before supplying the silicon raw material onto the substrate,
A method comprising irradiating a flame on the surface of the base material.
5. The method for manufacturing a silicon crystal plate according to any one of 4 to 4.