JP2883910B2 - Manufacturing method of single crystal silicon - Google Patents

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 single crystal silicon used as a material for semiconductors and solar cells.

[0002]

2. Description of the Related Art High-quality single-crystal materials, especially large-sized single-crystal silicon, are indispensable for the development of high-efficiency solar cells. At present, a single crystal silicon rod manufactured by the FZ method is considered to be the best as high quality single crystal silicon. This is because the CZ method, which is a single crystallization technique in line with the FZ method, cannot avoid defects due to oxygen contamination due to the use of a crucible. FIG. 2 shows a method for manufacturing a single crystal silicon rod using the FZ method.

The current method of manufacturing a single-crystal silicon rod using the FZ method uses a polycrystalline silicon rod 50 manufactured by the Siemens method as a raw material. Then, the material is inserted into the induction coil 40a while being partially melted to form a single crystal silicon rod 51. Single crystal silicon rod 5
1 is once again inserted into the induction coil 40b to form a single crystal silicon rod 52 as a product. The reason why the FZ melting is required twice is that the gas contained in the polycrystalline silicon rod 50, which is a material, cannot be sufficiently removed by one FZ melting, and the companies that develop and implement the FZ method Manufacturing manual also specifies two melts.

[0004]

In such a conventional manufacturing method, the essential properties of the manufactured single-crystal silicon rod, such as the lifetime and specific resistance, of the solar cell are high. However, the high cost and the high product price are major bottlenecks in manufacturing large materials for solar cells. There are three main reasons why the manufacturing method of the single crystal silicon rod using the FZ method is expensive.

[0005] First, the production cost of a polycrystalline silicon rod as a material, that is, the production cost by the Siemens method is high. Second, the outer diameter accuracy of the polycrystalline silicon rod manufactured by the Siemens method is poor, and the outer surface must be cut in large quantities when performing FZ melting.
That loss is large. Third, two FZ dissolutions are required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing single crystal silicon in which a single crystal quality comparable to the conventional FZ method can be obtained at a much lower cost.

[0007]

The Siemens method described above is currently dominant as a method for producing polycrystalline silicon rods, but this method is basically a batch type and has low efficiency. In addition, there are disadvantages that the silicon deposition surface area is small compared to the furnace capacity, and heat dissipation from the furnace surface is large. Therefore, this method is costly. Therefore, recently, the fluidized-granulation method has been attracting attention as a method of producing crystalline silicon instead of the Siemens method, and the present applicant is also proceeding with its development (Japanese Patent Application No. 63-32401).
0, Japanese Patent Application No. 1-100929, Japanese Patent Application No. 1-1099
No. 30, etc.).

[0008] The fluidized-granulation method is a method in which granular polycrystalline silicon is continuously grown in a reactor and extracted out of the reactor, so that the method is essentially higher than the batch type Siemens method. Efficiency, and the ratio of the silicon deposition surface area to the internal capacity of the reactor is remarkably large, which is extremely advantageous in terms of productivity and power consumption. Therefore, the manufacturing cost is much lower than the Siemens method.

While the present applicant has been developing a method for producing polycrystalline silicon by the fluidized-granulation method, the present applicant has also continued to develop a method for producing single-crystal silicon using continuous casting by electromagnetic induction. This time, it has been revealed that the combination of the fluidized-granulation method, the continuous casting method using electromagnetic induction, and the FZ method is extremely reasonable and economical as a method for producing high-quality single-crystal silicon.

[0010] In recent years, inexpensive solar cell grade silicon materials have been developed as a raw material silicon by a carbon reduction method, and it is considered that if this material is put to practical use, a crushed product thereof can be used similarly.

The method for producing single-crystal silicon of the present invention is characterized in that a polycrystalline silicon rod produced by continuous casting by electromagnetic induction using granular polycrystalline silicon as a raw material is single-crystallized by the FZ method.

[0012]

According to the continuous casting method by electromagnetic induction, a conductive bottomless crucible having at least a part in the axial direction divided in a circumferential direction is installed in an induction coil, and the material is melted and melted therein. Is solidified and pulled downward from the bottomless crucible to form a long rod. This method
Since the material in the bottomless crucible is not in contact with the inner surface of the crucible, when used for manufacturing a polycrystalline silicon rod,
There is an advantage that contamination from the crucible can be completely prevented.

The United States has filed a patent application in Japan based on this idea with a method for producing polycrystalline silicon using continuous casting by electromagnetic induction (Japanese Patent Application Laid-Open No. Sho 61-52962). The development for industrialization is continued (Japanese Patent Application Laid-Open Nos. 1-264920 and 2-306).
No. 98, etc.).

In the combination of the granular silicon raw material, the continuous casting method by electromagnetic induction and the FZ method, not only the polycrystalline silicon rod to be provided for the FZ method is produced at low cost, but also the quality is high, and the polycrystalline silicon rod is produced by the conventional Siemens method. An ultra-high-quality single-crystal silicon rod comparable to the case where FZ melting is performed twice on the obtained polycrystalline silicon rod is obtained by one FZ melting. In addition, when the polycrystalline silicon rod is subjected to the FZ method, a large amount of outer surface cutting is not required unlike the polycrystalline silicon rod manufactured by the Siemen method. Therefore,
Ultra-high quality single crystal silicon rods are manufactured at extremely low cost.

[0015]

The present invention will be described below with reference to examples.

As shown in FIG. 1, in the method for producing single-crystal silicon of the present invention, when performing continuous casting by electromagnetic induction, granular polycrystalline silicon produced by a fluidized-granulation method or the like is used as a raw material. 10 is used.

The method of continuous casting by electromagnetic induction is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 1-264920 and 2-3.
No. 0698 and the like. Briefly, a cylindrical bottomless crucible 20 and an induction coil 30 are installed in a vacuum chamber (not shown). The bottomless crucible 20
For example, a water-cooled copper crucible is divided in the circumferential direction except for the upper end. The induction coil 30 is fitted concentrically to the divided portion 21 of the bottomless crucible 20 with a gap. The granular polycrystalline silicon 10 charged into the bottomless crucible 20 from the hopper 35 is melted in a non-contact state with respect to the inner surface of the bottomless crucible 20. Then, the raw material supply into the bottomless crucible 20 and the bottomless crucible 20 accompanied by solidification of the dissolved raw material.
By continuing the downward pulling, a polycrystalline silicon rod 11 (unidirectionally solidified ingot of silicon) is manufactured.

The manufactured polycrystalline silicon rod 11 is
Since the outer diameter is determined by the inner diameter of the bottomless crucible 20, the outer diameter has a uniform outer diameter over the entire length and can be finished to the outer diameter necessary for FZ melting only by slightly cutting the outer surface. In the FZ melting, a polycrystalline silicon rod 11 whose outer surface is finished is inserted into an induction coil 40 to form a single crystal silicon rod 12.

At present, the price of the granular polycrystalline silicon 10 manufactured by the fluid granulation method is approximately half the price of the polycrystalline silicon rod manufactured by the Siemens method, and If battery-grade silicon is put into practical use, the price of granular polycrystalline silicon 10 is expected to further decrease. Therefore, even if the cost required for continuous casting by electromagnetic induction is included, the cost required for manufacturing the polycrystalline silicon rod 11 can be suppressed to the same level as the manufacturing cost based on the Siemens method.

In addition, a polycrystalline silicon rod 11 manufactured by continuous casting by electromagnetic induction using granular polycrystalline silicon 10 as a raw material has higher quality than a polycrystalline silicon rod manufactured by the Siemens method. Single crystal quality is assured in one FZ melt, as good as when the rod is subjected to two FZ melts. In addition, the polycrystalline silicon rod 11 has a higher outer diameter accuracy than the Siemens rod, the amount of cutting of the outer surface when supplying the FZ melt is drastically reduced, and the FZ melt only needs to be performed once. The cost of the silicon rod 12 is significantly reduced.

Table 1 is a comparison table showing the cost and quality when a single crystal silicon rod having an outer diameter of 5 inches is manufactured for the method of the present invention and the conventional method. Table 2 shows the production conditions in the method of the present invention.

[0022]

[Table 1]

[0023]

[Table 2]

As shown in Table 1, in the method of the present invention, since the quality of the polycrystalline silicon rod is high, the quality equivalent to the conventional twice melting is ensured by one FZ melting. The economic difference is remarkable. The reason why the quality of the polycrystalline silicon rod is excellent in the method of the present invention is considered as follows.

In the Siemens rod, since the deposition of silicon by the gas phase reaction is progressing, a small amount of chlorine or hydrogen, which is a reaction product, is taken into the silicon rod. These gas components are the first F
When Z is dissolved, it evaporates in the gas phase as a bumping gas, disturbs the stable holding state of the silicon melt dissolved in the zone, and hinders the growth of high-quality silicon single crystals. On the other hand, since the electromagnetically cast silicon polycrystalline rod has already released all gas components to be volatilized in the first melting at the time of electromagnetic casting, there is no factor that hinders the stable holding of the silicon melt during the FZ melting. For this reason, a high-quality silicon single crystal can be grown only by subjecting the electromagnetically cast polycrystalline rod to one FZ melting.

[0026]

As is clear from the above description, the method for producing single-crystal silicon of the present invention is remarkably excellent in economical efficiency.
In addition, sufficient quality can be ensured as a material for a high-efficiency solar cell or the like, which greatly contributes to the development of a high-efficiency solar cell or the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing step by step an implementation procedure of the method of the present invention.

FIG. 2 is a schematic diagram for explaining a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Granular polycrystalline silicon 11 Polycrystalline silicon rod 12 Single crystal silicon rod 20 Crucible without bottom 30, 40 Induction coil

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-9886 (JP, A) JP-A-2-233514 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 1/00-35/00

Claims (2)

(57) [Claims] 1. A method for producing single-crystal silicon, wherein a polycrystalline silicon rod produced by continuous casting by electromagnetic induction using granular polycrystalline silicon as a raw material is monocrystallized by an FZ method. 2. The method according to claim 1, wherein the raw material is granular polycrystalline silicon produced by a fluid granulation method.