JP2003277040A - Method for purifying silicon and solar cell manufactured using silicon purified by the method - Google Patents

Abstract

(57) [Summary] [Problem] To purify roughly purified metallic silicon to a purity of about 7-ine to efficiently and efficiently produce silicon for a solar cell.
Offer cheaply. SOLUTION: The silicon refining method of the present invention is a silicon refining method for removing impurities such as boron from molten silicon, comprising the steps of purifying molten silicon with molten slag, and melting with a gas containing an oxidizing gas. Purifying silicon. At least one selected from the group consisting of a gas containing an oxidizing gas, molten slag, and molten silicon is preferably stirred.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying silicon. In particular, it relates to a low-cost method for purifying silicon for solar cells.

[0002]

2. Description of the Related Art Utilization of natural energy has been drawing attention as an alternative to petroleum due to environmental problems. Among them, solar cells that use the principle of photoelectric conversion of silicon semiconductors have the characteristic that solar energy can be easily converted into electricity, but the spread of solar cells will reduce the cost of solar cells, especially the cost reduction of semiconductor silicon. Is important.

High-purity silicon for semiconductor integrated circuits includes
Metallic silicon with a purity of 98% or more obtained by carbon reduction of silica is used as a raw material, and trichlorosilane (S
It is obtained by synthesizing iHCl ₃ ), purifying it by a distillation method, and then reducing it (Siemens method) 11-nine.
Use high purity silicon. However, this high-purity silicon is inevitably an expensive material because it requires a complicated manufacturing plant and uses a large amount of energy for reduction.

In order to reduce the cost of solar cells, direct metallurgical refining from metallic silicon has been attempted in parallel with recycling of high-purity silicon obtained from each step of manufacturing a semiconductor integrated circuit. . In recycling, when a polycrystalline silicon ingot is made from a raw material such as a silicon wafer or a CZ ingot scrap, it is purified by segregation by unidirectionally solidifying a silicon melt so that practical solar cell characteristics can be obtained. Has become. However, although purification by directional solidification from metallic silicon is excellent in that many impurity elements can be removed at the same time, exceptionally with respect to boron,
Since the segregation coefficient is as large as 0.8, solidification segregation cannot be efficiently performed in principle, and it is practically difficult to remove boron.

As a technique aiming at more efficient boron purification, there is a method in which boron is converted into boron oxide to be removed from the molten silicon by moving it to the gas phase. For example, in Japanese Patent No. 3205352, a method of accelerating the oxidation of boron by irradiating a molten silicon surface with plasma of a mixed gas containing steam gas and argon powder or hydrogen gas added to argon and further silica powder. Has been introduced. According to this method, boron oxide can be vaporized and removed at a high temperature. However, since the portion that causes the plasma reaction must be local because of the configuration of the device, the device becomes large and expensive, and long-term purification is required.

Japanese Patent No. 2851257 discloses CaO.
In addition, a method of oxidizing boron to purify it by introducing a large amount of slag containing SiO ₂ as a main component into molten silicon has been introduced. However, 10 pp of boron
To purify metallic silicon containing about m to 50 ppm and reduce the boron concentration to about 0.3 ppm required for silicon for solar cells, it is necessary to purify for about 9 hours and heat the slag. In addition to the need for extra energy to do so, a large amount of high-purity slag, which is about three times the amount of silicon, is indispensable, leading to higher costs.

In Japanese Unexamined Patent Application Publication No. 2001-58811, molten silicon is agitated by using a stirrer or Lorentz force, and a purified gas such as argon containing water vapor is blown to convert boron into an oxide to produce molten silicon. How to remove from is introduced. However, in principle, it is not a method in which the reaction is dramatically improved, and it cannot be expected to improve the purification efficiency.

As described above, the conventional method for purifying silicon is
Both have low purification efficiency, high cost, and are still difficult to put into practical use.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide silicon for solar cells efficiently and inexpensively by using crude purified metallic silicon as a raw material and purifying it to a purity of about 7-nine. To do.

[0010]

A method for purifying silicon according to the present invention is a method for purifying silicon for removing impurities such as boron from molten silicon, which comprises a step of purifying molten silicon with molten slag and an oxidizing gas. Refining the molten silicon with a gas containing.

Another method of refining silicon according to the present invention is characterized by including the steps of refining molten silicon with a gas containing an oxidizing gas and refining the molten silicon with molten slag.

Another method of refining silicon according to the present invention comprises the steps of refining molten silicon with molten slag, refining molten silicon with a gas containing oxidizing gas and molten slag, and using a gas containing oxidizing gas. And a step of refining molten silicon.

At least one selected from the group consisting of a gas containing an oxidizing gas, molten slag and molten silicon is preferably stirred.

The solar cell of the present invention is characterized by being manufactured using silicon purified by any of these methods.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The method for purifying silicon according to the present invention comprises:
After the molten silicon is refined with the molten slag, the molten silicon is refined with a gas containing an oxidizing gas. Purification by molten slag is a method of removing boron by oxidizing boron as an impurity and incorporating boron oxide in the liquid phase into the slag, and a gas containing an oxidizing gas (hereinafter, also referred to as “purified gas”). Purification by means of a) is a method of removing boron by oxidizing boron and vaporizing the oxidized boron. In the present invention, although metallic silicon contains many kinds of impurities, attention is paid to boron, which is one of the contained impurities, and the same molten silicon is produced by two common methods in that it is a purification method based on the oxidation reaction of boron. By purifying, it is intended to provide a practical method for removing boron, which has high purification efficiency and low cost. That is, after refining the molten silicon with the molten slag and then refining the molten silicon with a gas containing an oxidizing gas, boron is removed by slag refining when the amount of impurities at the beginning of refining is high, and the amount of boron is reduced. Purification efficiency is improved by refining with a gas containing an oxidizing gas at the stage. Also,
Generally, slag contains a large amount of impurities, while high-purity materials such as argon (Ar) and water vapor are easily available. Therefore, by following this purification order, the impurities due to slag at the stage of purification progress You can prevent carry-on.

In carrying out the purification method of the present invention, the apparatus shown in FIG. 1 is typically used. In the example shown in FIG.
The wall of the refining furnace 1 is made of stainless steel, and the crucible 2 into which the raw material silicon and slag are charged is made of graphite. Further, an electromagnetic induction heating device 3 is provided in the refining furnace 1, and the shaft 5 and
A stirrer comprising a rotating body 6 attached to the lower end of the shaft 5 and a rotary drive mechanism (not shown) attached to the upper part of the shaft 5, and stirring and mixing molten slag and molten silicon. You can A seal mechanism 8 is provided at a portion where the shaft 5 penetrates the wall of the refining furnace 1 in order to ensure the tightness of the refining furnace 1 and facilitate the rotation of the shaft 5. An elevating mechanism (not shown) is provided above the shaft 5 in order to immerse the rotating body 6 in the molten silicon in the crucible 2 at the time of refining and to pull up the rotating body 6 from the molten silicon after the refining. Inside the shaft 5, there is a purified gas introduction passage 4 such as an oxidizing gas, and in the rotator 6, there is a purified gas outlet 7 communicating with the purified gas introduction passage 4. The shaft 5 and the rotating body 6 and the passage for introducing the purified gas may be separately provided. As shown in the example of FIG. 1, the shaft 5 is provided with the purified gas introduction passage 4, and the purified gas introduction port is further provided. 9 may be provided in the refining furnace 1.

The material to be purified according to the present invention is industrially widely used metal silicon having a purity of 98% or more, slightly high purity silicon after directional solidification purification, silicon after de-P (phosphorus) removal, high purity. For example, it is a mixture of silicon and low-purity silicon.

In the method for purifying silicon according to the present invention, molten silicon is first purified by slag. Purification by slag is one of the metal refining methods, and slag is added to a material to be purified and reacted with the material to be purified to remove impurities such as boron. The main function of slag is to purify silicon by, for example, decomposing slag component SiO ₂ in molten silicon, supplying oxygen into molten silicon, oxidizing boron in molten silicon, and removing it as boron oxide. To be done. In addition to boron as the impurity element to be removed,
There is carbon etc.

The slag is composed of silicon oxide (SiO ₂ ), calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ).
The binary slag of SiO ₂ and CaO is included in the slag. Among these, it is preferable to use a slag containing silicon oxide (SiO ₂ ) having a strong oxidizing function as a main component in terms of high purification efficiency. For example, silicon oxide (SiO ₂ ) and calcium oxide (C
aO) mixed with slag,
As is clear from the binary phase diagram of silicon oxide-calcium oxide, slag, which is a mixture of silicon oxide and calcium oxide, can be brought into a molten state at 1436 ° C. or higher, which is slightly higher than the melting point of silicon which is 1414 ° C. By using slag as molten slag instead of powder slag,
It is preferable because a large amount of oxidizing agent required for purification can be introduced into the reaction system.

The viscosity of the molten slag is about 1 Pa · s in the case of the mixed slag of silicon oxide and calcium oxide, which is higher than the viscosity of the molten silicon of about 0.001 Pa · s, and the slag is higher than that of silicon. Since the specific gravity is large, the slag tends to settle in the silicon-slag melting system. Magnesium oxide (MgO), barium oxide (BaO), lithium oxide (Li ₂ O), calcium fluoride (CaF ₂ ), etc. are appropriately added so as to have properties such as melting point, viscosity, and specific gravity suitable for refining silicon raw material. Although it can be added, it is preferable to reduce the melting point or the viscosity without significantly impairing the effect of the slag as an oxidizing agent. Therefore, a part or all of the calcium oxide should be replaced with magnesium oxide, calcium fluoride or lithium oxide. Is more preferable. However, due to the difference in properties between the molten slag and the molten silicon, the molten slag tends not to be easily mixed with the molten silicon even when the constituent components of the slag are changed. Therefore, it is preferable to stir at least one of the molten slag and the molten silicon. By stirring, the boron removal reaction can be promoted uniformly and efficiently.

After refining with the molten slag, the molten slag is taken out. To take out the slag, first, in the case where the melt is stirred in the refining process using the slag, in FIG. 1, the shaft 5 and the rotating body 6 are pulled up from the molten silicon by the elevating mechanism, and the molten silicon is allowed to stand. The molten slag is settled on the bottom of the crucible 2. At this time, if the power of the lower part 3c of the electromagnetic induction heating device 3 (the electromagnetic induction heating device 3 is composed of the upper part 3a, the middle part 3b and the lower part 3c) is lowered to increase the viscosity of the molten slag 10, It is preferable because it is easy to take out the slag. Next, open the gate valve 18,
From the tap 16 the molten silicon part with a lighter specific gravity
After transferring to another container similar to the container shown in FIG. 1, it is preferable to perform the following purification on the molten silicon in the other container. Alternatively, once the molten silicon in the supernatant is
Remove the slag by transferring it to the first separate container, transferring the molten slag at the bottom to the second separate container, and then returning the molten silicon from the first separate container to the original container. You can also The high viscosity slag at the bottom may be removed with a ceramic rake-shaped scraping tool or the like.
As the simplest method of taking out slag, a method of lowering the heat resistant pipe from above to the bottom of the crucible and suctioning and removing the slag at the bottom in a stationary state after stopping stirring is preferable.

After taking out the slag, the molten silicon is refined with a gas containing an oxidizing gas. Gas containing oxidizing gas is
A purified gas containing water vapor, oxygen, or a gas containing an oxygen atom such as carbon monoxide, or a halogen-based gas such as hydrochloric acid, including a broadly defined oxidation reaction. The gas containing an oxidizing gas may be based on an inert gas such as argon as a carrier gas. In addition, a gas containing hydrogen gas is also preferable in terms of controlling the reaction state.
The water vapor is added, for example, by using a humidifier to adjust the gas dew point to 20 ° C. to 90 ° C., and thus 2% by volume to 70%.
Water vapor can be easily added within the range of volume%. Even when refining molten silicon with a gas containing an oxidizing gas, it is preferable to stir at least one of the gas containing an oxidizing gas and the molten silicon in order to make the refining uniform and improve the refining efficiency. .

The solar cell of the present invention is manufactured at low cost because it is manufactured by using low-cost silicon purified by such a method.

Another method for purifying silicon of the present invention is to purify molten silicon with a gas containing an oxidizing gas and then purify molten silicon with molten slag. By purifying the same material by two types of methods, that is, purification with a gas containing an oxidizing gas and purification with slag, it is possible to improve the purification efficiency and to carry out practical boron purification at low cost. That is, by performing the step of refining the molten silicon with the molten slag after the step of refining the molten silicon with the gas containing the oxidizing gas, the gas containing the oxidizing gas causes the boron in the molten silicon to be oxidized in the gas phase. Since it is converted into boron and removed in advance, the amount of liquid-phase boron oxide taken into the slag in the subsequent step can be reduced, and the purification efficiency of silicon as a whole can be improved.

The solar cell of the present invention is manufactured at low cost because it is manufactured by using low-cost silicon purified by such a method.

Another method for purifying silicon of the present invention is to purify molten silicon with molten slag, then purify molten silicon with a gas containing oxidizing gas and molten slag, and then to gas containing oxidizing gas. To refine molten silicon.
By introducing a gas containing an oxidizing gas in the refining stage by molten slag, boron in silicon is oxidized, boron oxide in liquid phase is transferred to slag, and further transferred to gas phase to remove boron. . The liquid-phase boron oxide that has transferred to the slag is removed from the slag as gas-phase boron oxide by the gas containing the supplied oxidizing gas, so it can be efficiently removed from silicon without increasing the boron concentration in the slag. Boron can be removed. Therefore, it is the purification method that gives the greatest effect.

The preferred steps of the purification method are shown in FIG. Purification of silicon is mainly purification by slag 1
And purification 2 centered on purification with a purified gas. In the first stage 1 of the refining 1, the silicon to be refined and the slag are charged into a refining furnace and heated until the silicon and the slag are in a molten state. Purification by slag is started from this state.

In step 2, the purified gas is introduced into the molten silicon, molten slag. The purified gas is a gas containing an oxidizing gas. At this stage, the boron removing effect by the purified gas is added to the boron removing effect by the molten slag, and the refining effect is further increased. When the silicon raw material containing boron and slag are mixed into a molten state and the purified gas is blown into the molten silicon to analyze the molten slag and the boron concentration in the molten slag collected before and after the refining process, the molten slag is analyzed. Both the boron concentration before and after refining is about 3 ppm, and although the boron concentration in the molten slag is not increased, the boron concentration in the molten silicon is significantly reduced. In the case of refining with both the molten slag and the purified gas, the time required for removing boron is reduced to about 1/3 or less as compared with the case of refining with only the molten slag or with the purified gas only. be able to. In introducing the purified gas, it is preferable to stir the silicon melt or the like because it has the effect of enhancing the purification efficiency.

In step 3, the molten slag is removed from the refining system. Thus, once the molten slag is removed, in the stage 4 of the refining 2 with the molten slag removed,
Since purification can be performed with a purified gas, it can be highly purified. Also in the purification in step 4, stirring of the silicon melt or the like is preferable because it has the effect of enhancing the purification efficiency. Depending on the impurity species and content of the crude metallic silicon, other purification methods may be carried out in addition to the purification of the present invention.

The steps from Step 1 of Purification 1 to Step 4 of Purification 2 will be described in order with reference to FIG.

In the step 1 of heating and melting process of silicon and slag, first, the inside of the refining furnace 1 is set to an inert gas atmosphere such as argon and heated by the electromagnetic induction heating device 3, so that the heat is transferred through the crucible susceptor 13. The temperature of the raw material silicon and the slag rises due to the heat, and they finally melt. The melt thus formed is maintained at a predetermined temperature by using the heat insulating material 14 for crucible and the heat insulating material 17 for gate valve. At this stage, the molten silicon is separated into the upper layer and the molten slag is separated into the lower layer.

In the step 2 of introducing and stirring the purified gas, the shaft 5 is lowered by an elevating mechanism (not shown), and the purified gas is introduced through the purified gas introduction passage 4 into the rotating body 6.
The rotor 6 is immersed in the molten silicon while being blown out from the purified gas blowout port 7. At this time, the purified gas introduction pressure is
For example, by setting the pressure in the range of about 0.15 MPa to 0.3 MPa and making it higher than the atmospheric pressure, stable gas supply can be continued even when mixing molten slag with high viscosity. After lowering the rotating body 6 near the lower layer of the molten silicon, preferably near the interface between the molten slag and the molten silicon,
The shaft 5 is rotated by a rotary drive mechanism (not shown). It is preferable that the purified gas and the molten slag are agitated by the rotation of the shaft 5 while the purified gas is blown out from the purified gas blowout port 7 to be finely divided and uniformly dispersed. Due to the stirring, the molten silicon 15, the molten slag 10, and the purified gas 11 are mixed very efficiently, and the contact interface is significantly increased. The oxygen supplied from the purified gas 11 and the molten slag 10 causes the molten silicon 15 to melt. The oxidation reaction of boron inside is promoted. The vaporized boron oxide or the like is discharged from the exhaust pipe 12.

The slag removing step of step 3 is performed in the same manner as described above. In the next step 4 of introducing and stirring the purified gas, the slightly remaining molten slag and molten silicon are heated to a desired temperature again, the top wall 1a and the gate valve 18 are closed, and the purified gas of the rotating body 6 is closed. The shaft 5 is lowered by an elevating mechanism until the outlet 7 reaches near the center of the depth of the molten silicon, and while the purified gas such as argon gas containing water vapor is introduced, the rotating body 6 is rotated and the purified gas is melted into the molten silicon. The mixture is stirred and mixed therein, and the boron in the molten silicon is oxidized and removed for purification.

The effectiveness of the method of purifying with the purified gas after the step of purifying the molten silicon with the purified gas and the molten slag, that is, the method of removing the molten slag from the molten silicon to the outside of the reaction system during the purification is The following are technically inferred. As the purification of molten silicon progresses, the SiO ₂ component forming the slag is consumed to oxidize boron, the removal rate of impurities from the molten silicon decreases, and the oxygen supply capacity to the molten silicon eventually disappears. . Further, the boron originally contained in the slag is mixed in the purified molten silicon, which deteriorates the purity of the molten silicon. Therefore, it is considered effective to remove the molten slag out of the reaction system before the removal rate of impurities in the molten slag decreases.

The solar cell of the present invention is manufactured at low cost because it is manufactured by using low-cost silicon purified by such a method.

[0036]

Example 1 Boron 65 pp was used as a raw material silicon to be purified.
m-containing scrap silicon and semiconductor grade silicon (1
1-nine) was mixed in a mass ratio of 1: 8 to prepare silicon having a boron concentration of 7 ppm. Also,
As the slag, silicon oxide powder and calcium oxide powder were blended at a mass ratio of 65:35 to prepare a slag having a boron concentration of 3 ppm. Boron concentration is IC
It was measured by P emission analysis.

Slag was added to the raw material silicon in an amount of 20% by mass of the raw material silicon, and the total amount was set to 1 kg, and the raw material silicon was charged into the crucible 2 of the refining furnace 1 as shown in FIG. The inside of the refining furnace 1 was set to 1 atmosphere of argon gas atmosphere, and the crucible 2 was heated by the electromagnetic induction heating device 3 to melt the raw material silicon and slag and hold the temperature at 1550 ° C. Since the molten slag has a large specific gravity with respect to the molten silicon, it was deposited on the bottom of the crucible 2.

Purified gas having a water vapor content of 30% by volume in argon gas is blown from the purified gas blowing port 7 of the rotating body 6 at a flow rate of 1 L / min, and the purified gas blowing port 7 of the rotating body 6 is melted by slag. The shaft 5 was lowered by the elevating mechanism until reaching the vicinity of the interface between the molten silicon and the molten silicon, and then the shaft 5 was rotated at 400 rpm to perform purification for 1 hour.
Next, after taking out the molten slag from the molten silicon,
The shaft 5 was immersed in molten silicon, and the purified gas was blown out from the purified gas blowing port 7 of the rotator 6 under the same conditions as described above, and the purification was further continued for 1 hour. When the boron concentration after purification was measured, it was 0.3 ppm. The result is shown in FIG.

Example 2 Silicon was purified under the same conditions as in Example 1 except that no purification gas was introduced in the slag purification step. When the boron concentration after purification was measured, it was 0.4 ppm, which was slightly higher than that in the case of Example 1. The result is shown in FIG.

Example 3 In FIG. 1, as in Example 1 except that the purified gas was introduced into the purification furnace 1 through the purified gas inlet 9 and the purified gas was not introduced through the purified gas outlet 7 of the rotor 6. Purification of silicon was performed under the same conditions. When the boron concentration after purification was measured, it was 0.6 ppm. The result is shown in FIG.

Example 4 In FIG. 1, the purified gas was introduced into the refining furnace 1 through the purified gas inlet 9 and the purified gas was not introduced through the purified gas blowout port 7 of the rotating body 6 with the example 2. Purification of silicon was performed under the same conditions. When the boron concentration after purification was measured, it was 0.7 ppm. The result is shown in FIG.

Comparative Example 1 Silicon was purified under the same conditions as in Example 1 except that the molten slag was not taken out. The boron concentration after purification was 0.8 ppm, but the boron concentration in the molten silicon one hour after the start of purification was 1.7 p.
It was pm. The result is shown in FIG. As is apparent from FIG. 3, the reduction of boron was good until 1 hour after the start of purification, but the reduction rate of boron became slower 1 hour after the start of purification due to the residual slag. I understood it. It is considered that this is because the boron originally contained in the molten slag moved into the purified molten silicon and hindered the improvement of the purity of the molten silicon.

Comparative Example 2 Silicon was purified under the same conditions as in Example 1 except that a purified gas containing water vapor was not used during the purification. The concentration of boron after purification was 1.8 ppm. The result is shown in FIG.

Example 5 Purified molten silicon was poured into a mold according to Example 1 and cast to produce an ingot, which was sliced with a wire saw to obtain a polycrystalline silicon substrate having a plate thickness of 330 μm and a 10 cm square. did. Cell formation was performed by a known process. The substrate surface was textured by alkali etching.
A pn junction was formed on the light-receiving surface side by n ⁺ diffusion with POCl ₃ . A SiN antireflection film was formed on the surface by the CVD method. The front surface is masked and the back surface is acid-etched
After removing the ⁺ layer, a back electrode was formed, and a comb-shaped metal electrode was printed and baked on the surface to manufacture a solar cell. Table 1 shows the characteristics of the prepared solar cells.

[0045]

[Table 1]

Comparative Example 3 A solar cell was prepared in the same manner as in Example 5 except that a commercially available polycrystalline silicon substrate (scrap silicon) was used instead of the silicon purified in Example 1. Table 1 shows the characteristics of the prepared solar cells.

As is clear from the results of Table 1, Example 5
The solar cell prepared in 1. exhibited almost the same characteristics as a solar cell using commercially available silicon as a raw material.

The embodiments and examples disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0049]

According to the present invention, the effect of gas refining is added to the effect of removing boron by molten slag, and the refining effect of silicon is further increased. For example, when a silicon raw material containing boron and slag are mixed into a molten state and a refined gas containing water vapor is blown into the molten silicon for purification, no increase in the boron concentration in the molten slag is observed. Nevertheless, the boron concentration in the molten silicon is significantly reduced. Also, when refining with both molten slag and purified gas, when refining only with molten slag,
Alternatively, the time required for removing boron is greatly reduced to ⅓ or less as compared with the case where only the purified gas is used for purification.

When at least one of the gas containing the oxidizing gas, the molten slag and the molten silicon is stirred, the efficiency of purification can be improved.

Therefore, according to the present invention, it is possible to provide crude silicon metal for a solar cell efficiently and inexpensively by purifying it to a purity of about 7-nine.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a typical apparatus for carrying out the purification method of the present invention.

FIG. 2 is a process drawing showing the purification method of the present invention.

FIG. 3 is a diagram showing boron concentrations before and after purification.

[Explanation of symbols] 1 refining furnace, 2 crucibles, 3 electromagnetic induction heating device, 4
Purified gas introduction passage, 5 axes, 6 rotating bodies, 7 purified gas outlet, 8 sealing mechanism, 9 purified gas inlet, 10
Molten slag, 11 purified gas, 12 exhaust pipe, 13 crucible susceptor, 14 heat insulating material for crucible, 15 molten silicon, 16 tap opening, 17 heat insulating material for gate, 18 gate valve.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoshi Hayakawa             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Toru Nunoi             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 4G072 AA01 BB12 GG01 GG03 HH01                       HH38 LL05 MM08 MM38 UU02                 5F051 AA03 CB05 CB20 CB30 DA03                       GA02 GA15

Claims (5)

[Claims] 1. A method for purifying silicon for removing impurities such as boron from molten silicon, comprising a step of purifying the molten silicon with molten slag, and a step of purifying the molten silicon with a gas containing an oxidizing gas. A method for purifying silicon, comprising: 2. A method of purifying silicon for removing impurities such as boron from molten silicon, comprising a step of purifying the molten silicon with a gas containing an oxidizing gas, and a step of purifying the molten silicon with molten slag. A method for purifying silicon, comprising: 3. A method of purifying silicon for removing impurities such as boron from molten silicon, a step of purifying the molten silicon with a molten slag, and a step of purifying the molten silicon with a gas containing an oxidizing gas and the molten slag. And a step of purifying the molten silicon with a gas containing an oxidizing gas, the method for purifying silicon. 4. The method for purifying silicon according to claim 1, wherein at least one selected from the group consisting of a gas containing an oxidizing gas, molten slag and molten silicon is stirred. 5. A solar cell manufactured using silicon purified by the method according to claim 1.