JPH0741393A - Production of silicon sheet by continuous casting - Google Patents

Abstract

PURPOSE:To avoid the fusion of molten silicon to a casting mold and continuously produce a silicon sheet by using the mixed sintered compact of silicon nitride and boron nitride as the material for the mold. CONSTITUTION:Molten silicon 14 is supplied to a horizontal heated casting mold 12 with the upper surface opened, the molten silicon 14 is cooled and crystallized on the end of the horizontal surface 36 of the mold 12 to form a silicon sheet which is continuously pulled out in the horizontal direction, and a long-sized silicon sheet is continuously produced by casting. The mixed sintered compact of silicon nitride and boron nitride is used as the material for the mold 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting a silicon (Si) plate used for semiconductors, solar cells and the like.

[0002]

2. Description of the Related Art Si plates are usually single crystal or polycrystal S.
It is made by slicing an i ingot. However, in order to reduce the cost, there is a demand for a technique of directly producing a Si plate from molten Si by omitting the slicing step, and in the past, EFG (Edge-Defined, Film-F) has been demanded.
ed Growth) method, HRG (Horizonta)
The Ribbon Growth method, the cast ribbon method, and the like have been studied.

In the EFG method, as shown in FIG.
The quartz crucible 116 in the susceptor 112 is heated by the high-frequency heating coil 110, and Si is heated in the quartz crucible 116.
To melt. The molten Si 14 is pulled up through the material flow path of the graphite die 118 vertically provided in the quartz crucible 116, and then comes out of the susceptor 112 to become the Si plate 20. However, in this EFG method, since graphite having a good wettability with molten Si is used as the die material, graphite of the die material is mixed with crystalline Si, and it is not possible to expect high purification of the Si plate. Since the flatness of the plate is poor, there is a drawback such as poor stability in continuous production.

In the HRG method, as shown in FIG.
The molten Si 14 is melted in the melting tank 124 heated by the heating element 122.
And a cooling device 1 provided above the melting tank 124.
A cooling gas is blown from 26 to cool and crystallize the molten metal surface of the molten Si 14. The crystallized Si plate 20 is continuously drawn out in the horizontal direction by the guide roll 128, and the plate thickness is adjusted by the mold roll 130. However, in this HRG method, the Si crystal is molten Si14.
Since it grows vertically below the molten metal surface, it is very difficult to control the thickness of the Si plate.

In the cast ribbon method, as shown in FIG. 5, molten Si 14 is cast with argon (Ar) gas into the mold 1.
S that was pressed into 32 and crystallized in cavity 134
The i-plate 20 is pulled out in the horizontal direction using the pull-out jig 136. However, this cast ribbon method has a defect that the solidified Si is caught in the cavity 134 due to the volume expansion of the molten Si at the time of solidification, and the solid Si cannot be continuously drawn out.

[0006]

Therefore, the inventors of the present invention supply molten silicon to a horizontal heating mold having an open upper surface, and cool and crystallize the molten silicon on the horizontal end of the mold to form a silicon plate. Forming and continuously pulling out the silicon plate in the horizontal direction to manufacture the silicon plate.
Attention was paid to SC (Ohno Strip Casting) method. In this method, since the growth surface of the Si crystal is not in contact with the mold, the Si surface is very flat.
The plate is continuously formed, and the plate thickness can be easily controlled by the depth of the molten metal (molten Si) on the horizontal surface of the mold, and since the mold with the open top is used, the volume expansion of Si during solidification I can handle it without any problems. However, when a commonly used ceramic mold, that is, a mold made of a material such as graphite, silicon carbide, silicon nitride, alumina, magnesia, or mullite is used, it reacts with molten Si and causes fusion. The crystallization of Si proceeds from the mold side, and as a result, plate-shaped Si cannot be continuously cast. Further, when a sintered body of boron nitride is used as a mold, the degree of fusion bonding with Si is reduced, but the mechanical strength as a mold is poor, which is not preferable for practical use.

[0007]

As a result of earnest research, the inventors of the present invention have found that the above problems can be solved all at once by using a mixed sintered body of silicon nitride and boron nitride as a material for a mold. The present invention has been completed.

That is, according to the present invention, molten silicon is supplied to a horizontal heating mold having an open upper surface, and the molten silicon is cooled and crystallized on a horizontal end portion of the mold to form a silicon plate. A continuous casting method for producing a long silicon plate by continuously pulling out in a direction, characterized by using a mixed sintered body of silicon nitride and boron nitride as a material of the mold.

In the mixed sintered body of silicon nitride and boron nitride, if the content of boron nitride is less than 10% by weight, a reaction with molten Si occurs, and fusion is apt to occur, which is not preferable. On the other hand, if it exceeds 80% by weight, the mechanical strength of the sintered body is extremely lowered, which is not preferable as a mold material. Therefore, the content of boron nitride is preferably 10 to 80% by weight, more preferably 20 to 60% by weight.

Further, when molding a mold of a mixed sintered body of silicon nitride and boron nitride, a sintering aid such as yttria, alumina or aluminum nitride may be added within a range of 10% by weight or less.

In order to continuously draw out the silicon plate in the horizontal direction while forming the silicon plate, for example, a dummy plate is horizontally inserted into the mold from the outlet of the horizontal heating mold, and the molten Si supplied into the mold and the dummy plate are supplied. The dummy end is pulled out from the mold in a horizontal direction while the molten Si is horizontally solidified from the contact portion by contacting the insertion ends thereof.
As a result, a long Si plate is formed by sequentially solidifying and forming in the horizontal direction from the portion attached to the insertion end of the dummy plate.

As a casting atmosphere, an inert gas such as argon, helium, nitrogen or a mixed gas thereof is usually used in order to prevent the surface oxidation of the molten Si, but to further prevent the oxidation. Is hydrogen,
A reducing gas such as carbon monoxide, or a mixed gas thereof,
Alternatively, these reducing gases may be used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

1 and 2 are partially omitted sectional perspective views showing an embodiment of an apparatus for carrying out the manufacturing method of the present invention. This apparatus is a crucible 10 for melting Si, a horizontal heating mold 12 for casting a Si plate, a hot water supply pipe for connecting the crucible 10 and the horizontal heating mold 12 and supplying molten Si 14 from the crucible 10 to the horizontal heating mold 12. 16, a cooling device 18 provided above the horizontal heating mold 12, and the cast S
It comprises a pinch roll 22 for continuously pulling out the i-plate 20 in the horizontal direction.

The crucible 10 and the hot water supply pipe 16 are heated to a temperature equal to or higher than the melting temperature of Si by heating elements 24 and 26 provided on the outer circumferences thereof. In the crucible 10,
Control rod 2 having an outer diameter slightly smaller than the inner diameter of the crucible 10.
8 is inserted, and the control rod 28 allows the crucible 10 to be inserted.
The molten metal surface of the molten Si 14 inside is kept constant.

The horizontal heating mold 12 is formed of a mixed sintered body of silicon nitride and boron nitride (manufactured by Kawasaki Furnace Co., Ltd.) having a boron nitride content of 20% by weight. The amount of current supplied to the heating element 30 provided below the heating mold 12 is controlled to adjust the temperature to the solidification temperature of Si or higher. The bottom of the horizontal heating mold 12 is deepest at the inlet 32 of the molten Si, becomes gradually shallower toward the outlet 34, and becomes a horizontal surface 36 from the middle.

In order to manufacture a Si plate, the horizontal heating mold 12 is used.
While maintaining the temperature above the solidification temperature of Si, as shown in FIG.
The molten Si 14 is supplied to the horizontal heating mold 12 from the crucible 10 through the hot water supply pipe 16 while being inserted into the horizontal plane 36 from the outlet 34 to the inside. Then, the molten Si 14 flowing in from the inlet 32 of the horizontal heating mold is brought into contact with the tip (insertion end) 40 of the graphite dummy plate. Since the argon gas containing 5% of hydrogen is blown onto the upper surface of the graphite dummy plate 38 from the gas blowing pipe 42 of the cooling device 18 to cool the horizontal heating mold 12,
The molten Si 14 begins to solidify in the horizontal direction from the portion in contact with the tip 40 of the dummy plate made of graphite, avoiding the inner wall surface. Then, as shown in FIG. 2, by pulling the graphite dummy plate 38 to the right side in the drawing using the pinch roll 22, the Si plates 20 sequentially formed in the horizontal direction from the portion attached to the tip 40 of the dummy plate are removed. ,
Cooled by the gas blown from the gas blowing pipe 42, a long Si plate is continuously manufactured.

At this time, the thickness of the Si plate 20 is defined by the depth of the molten Si 14 from the molten metal surface 44 to the horizontal surface 36. Therefore, by changing the degree of insertion of the control rod 28 into the crucible 10 and adjusting the molten metal surface 44, the Si plate 2
The thickness of 0 can be changed.

In this embodiment, the crucible 10 for melting Si and the horizontal heating mold 12 are connected to each other by the hot water supply pipe 16. However, these crucible 10 and the horizontal heating mold 12 are nitrided with silicon nitride. It may be integrally formed by using a mixed sintered body of boron.

Although a graphite plate is used as the dummy plate 38, in order to cast a higher quality Si crystal plate, a Si single crystal is attached to the tip (insertion end) of the graphite dummy plate, It is preferable to use the Si single crystal plate itself as a dummy plate.

Further, in order to promote the casting of the Si plate more smoothly, a mold release agent such as boron nitride is applied to the horizontal surface 36 of the horizontal heating mold 12 and the horizontal heating mold 12 at the start of casting.
The releasability from can be increased.

[0022]

By using the mixed sintered body of silicon nitride and boron nitride as the mold material, fusion between molten Si and the mold can be avoided, and continuous casting of a Si plate by the OSC method becomes possible.

[Brief description of drawings]

FIG. 1 is a partially omitted sectional perspective view showing an embodiment of an apparatus for carrying out a manufacturing method of the present invention.

FIG. 2 is a partially omitted sectional perspective view showing an embodiment of an apparatus for carrying out the manufacturing method of the present invention.

FIG. 3 is a schematic cross-sectional perspective view illustrating an EFG method.

FIG. 4 is a schematic cross-sectional view illustrating the HRG method.

FIG. 5 is a schematic sectional view illustrating a cast ribbon method.

[Explanation of symbols]

 10 crucible 12 horizontal heating mold 14 molten Si 16 hot water supply pipe 18 cooling device 20 Si plate 22 pinch roll 24 heating element 26 heating element 28 control rod 30 heating element 32 inlet of horizontal heating mold 34 outlet of horizontal heating mold 36 of horizontal heating mold Horizontal surface 38 Dummy plate 40 Tip of dummy plate 42 Gas blowing pipe 44 Molten Si molten metal surface

Claims (2)

[Claims] 1. Molten silicon is supplied to a horizontal heating mold having an open upper surface, and the molten silicon is cooled and crystallized on a horizontal end of the mold to form a silicon plate, and the silicon plate is continuously continuous in the horizontal direction. A continuous casting method for producing a long-sized silicon plate by using the above-mentioned method, wherein a mixed sintered body of silicon nitride and boron nitride is used as a material for the mold, the method for manufacturing a silicon plate. 2. The method according to claim 1, wherein the content of boron nitride in the mixed sintered body of silicon nitride and boron nitride is 10 to 80% by weight.