KR20110005933A

KR20110005933A - The method for refining of metallurgical grade silicon to produce solar grade silicon

Info

Publication number: KR20110005933A
Application number: KR1020090063310A
Authority: KR
Inventors: 김영언
Original assignee: 조북룡
Priority date: 2009-07-13
Filing date: 2009-07-13
Publication date: 2011-01-20

Abstract

PURPOSE: A manufacturing method of a high purity silicon for a solar battery for implementing unidirectional solidification is provided to eliminate the boron with high segregation coefficient and refine since reducing the total around time. CONSTITUTION: A manufacturing method of a high purity silicon for the solar battery comprises next steps. A liquid state the metallurgical grade silicon(20) within a container is fused into the decompression container surrounding the metallurgical grade silicon with heater. The argon gas and the hydrogen gas including the steam are inspired within the liquid state metallurgical grade silicon. The thermal chemical reaction of the Si-B-P-Ar system is optimized. The boron and the liquid state within the metallurgical grade silicon impurity phosphorus are eliminated to the gas phase oxide HBO and PO.

Description

The method for refining of metallurgical grade silicon to produce solar grade silicon}

The present invention relates to a method for producing silicon, which is a raw material for solar cells, and more particularly, to a method for producing high purity silicon for solar cells having a purity of 6N or more suitable for solar cell grade silicon by purifying metal silicon having a purity of 2N at low cost. .

Global warming and high oil prices issue high interest in renewable energy, the government in renewable energy for fossil energy by focusing fostering new growth engines, depletion and energy crisis, domestic energy vulnerability line complements sources of energy (energy source) In solar power generation is supported by the government's subsidy for solar power generation, solar power facilities are in operation and under construction, and low-cost solar power generation, which has drastically reduced the cost of conventional solar power generation, is preparing for full-scale practical use. A solar cell using the photoelectric effect of a silicon semiconductor as a basic principle has a feature of easily converting solar energy into electricity. The cost down of solar cells, especially the cost down of semiconductor silicon, is very important for the expansion of solar power generation. Semiconductor grade silicon used in the manufacture of semiconductor ICs is made of SiHCl ₃ ( T ri c hloro s ilane (TCS)) with a silicon grade of at least 98% purity obtained by carburizing silica. After the conversion / synthesis, the silicon chloride is purified by distillation and then reduced by the so-called Siemens method to obtain high purity silicon of about 11N (99.999999999%). This Siemens method is complicated manufacturing plant equipment and very high energy cost in the production of silicon, the high purity silicon of the Siemens method is expensive to manufacture. For this reason, semiconductor-grade silicon is not suitable because of high manufacturing cost due to excessive purity, which is too high for solar cell applications that require an urgent cost down.

In order to reduce the cost of silicon for solar cells, UMG silicon (upgrading metallurgical grade silicon), which is made of metal grade silicon with purity 2N from metallurgical purification in an arc furnace, can be used for high purity silicon for solar cells. Purification by directional solidification during the manufacturing process is excellent in that many impurities can be removed simultaneously, except for boron (B) and phosphorus (P). As the segregation coefficient is 0.8 for boron (B), solidification segregation cannot be efficiently carried out in principle, so it is difficult to remove boron (B) in silicon, and the segregation coefficient is 0.35 for phosphorus (P). Difficult to remove

In the slag refining using a slag flocculant, impurity boron (B) in the metal-grade silicon, which is a molten liquid state, is firstly used to produce high-purity silicon suitable for solar cells, particularly high-purity silicon having a boron (B) content of at least 0.3 mass ppm or less. If silver is not oxidized, the movement to molten slag (slag phase) will not be promoted, so a slag flocculant material with high boron oxidizing power should be used, and secondly, the mass of boron (B) in the molten liquid metal mass% concentration A (% Considering the distribution ratio represented by the ratio (B / A) between boron (B) and mass concentration B (% B) in the dissolved slag, the slag coagulant material should be used at a relatively high ratio with respect to the metallic silicon. And thirdly, it is necessary to uniformly and efficiently heat the metallic silicon in the molten liquid state. The above-described slag refining requires a long refining time, requires unnecessary energy for heating the slag, and a high-purity slag flocculant, which is about several times the amount of metal-grade silicon, is inevitably very expensive and not realistic.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing high purity silicon for solar cells, which is made of metal grade silicon having a purity of 2N as a raw material and suitable for purification at a purity of about 6N at low cost.

The present invention melts metallic silicon and injects argon gas containing water vapor and hydrogen gas into liquid metallic silicon to remove the liquid impurity boron in silicon with gaseous oxide HBO, and the boron content is 0.3 ppm by mass or less. Its purpose is to provide a method for producing high purity silicon for solar cells.

The present invention melts metal-grade silicon, and among the impurities in the liquid metal-grade silicon, non-volatile impurities are converted into impurities such as sodium (Na), calcium (Ca), potassium (K), and aluminum (Al) as slag flocculants. Accordingly, an object of the present invention is to provide a method of manufacturing high purity silicon for solar cells, wherein the nonvolatile impurities are removed from the metallic silicon in the liquid state to the slag phase.

The present invention is to put a metal-grade silicon in a pressure-sensitive vessel surrounded by a heater and then melt the metal-grade silicon in the container with the heater to a liquid state, and then argon gas and hydrogen containing water vapor into the metal-grade silicon in a liquid state By blowing gas to optimize the thermochemical reaction of the Si-BPH ₂ O-Ar system, the liquid impurities in the metal-grade silicon, boron (B) and phosphorus (P) are removed with gaseous oxides HBO and PO, and at the same time The other impurities which do not become are the heat of the Na-Ca-K-Al-Si-O system using impurity sodium (Na), calcium (Ca), potassium (K) and aluminum (Al) as slag flocculants in the metallic silicon. Optimize the chemical reaction to remove the other impurities to remove the impurities in the metal-grade silicon, and then to unidirectionally solidify the metal-grade silicon in the liquid state in the container to the metal-grade silicon It is characterized by refining with high purity silicon having a purity of 6N or higher.

In order to remove boron and phosphorus having high segregation coefficients, the present invention blows Ar and H ₂ containing water vapor into molten metal-grade silicon to remove boron and phosphorus (P) and gaseous oxides HBO and Purification process to remove with PO and purification method to remove impurities in silicon into slag by using impurity in molten metal grade silicon as slag flocculant can be carried out by simultaneous reaction to reduce overall process time and can be purified at low cost. have.

The present invention will now be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a furnace used to make high purity silicon for solar cells, wherein furnace 10 has a vessel 12 containing furnace insulation 26 and liquid metal silicon 14. The vessel 12 is placed on a support block 16 in contact with a heat exchanger 18 in the form of a support rod. As shown in this figure, a typical tubular heat exchanger can be replaced by a mobile insulation pack 22 that can be moved relative to the support block 16. After putting the metal grade silicon into the container 12, the heater 20 of 10 is operated and the temperature of the container is set to 1450 ° C. to melt the silicon in the solid agglomeration state and to maintain the liquid metal grade silicon. Gas blowing into vessel 12 enters through nozzle 27, and the resulting gaseous and exhaust gases are vented out through nozzle 28. The degree of vacuum of the vessel 12 is operated by a vacuum pump (not shown) and the required degree of vacuum in the vessel 12, i.e., the reduced pressure, can be adjusted.

Water vapor is supplied through a gas humidifier (not shown), and Ar and H2 are supplied by Bombay (not shown).

Metallurgical grade silicon varies slightly depending on the supplier, but the purity of silicon is 99% to 99.7%, and the main impurities are iron (Fe), aluminum (Al), calcium (Ca) and titanium (Ti). ). Boron (B) and phosphorus (P) in metal-grade silicon are about 15-130 ppma and 27-45 ppma, respectively.

Most impurities in the molten metal grade silicon can be removed by directional solidification, which is a major purification process. Since most impurities have low segregation coefficients, coagulation segregation can be efficiently performed, so that molten metal grade silicon can be removed by only one-way solidification.

However, the most problematic impurities are boron (B) and phosphorus (P), which cannot be effectively removed by unidirectional solidification. Therefore, an additional purification process is required to remove boron (B) and phosphorus (P) before unidirectional solidification of the molten metal grade silicon. This additional refining process is preferred to remove all impurities, including boron (B) and phosphorus (P), from the molten metal grade silicon prior to one-way solidification, and especially boron content suitable for solar cell silicon properties with additional refining and one-way solidification. This high purity silicon of 0.3 mass ppm or less can be obtained.

A key point of the present invention is the purification process, which proceeds before unidirectional solidification, with further purification processes proceeding in a modified one-way solidification apparatus for silicon.

If you look at the further purification process,

Vacuum melt

The metallic silicon in the container is heated under reduced pressure to a molten state to remove volatile elements in the metallic silicon. Decompression melt is known to be an effective method for removing phosphorus (P).

Oxidation of Impurities in Metallic Silicon

When impurities in the molten metal grade silicon are oxidized to become oxides, materials formed like oxides are more stable than those remaining as impurity elements in the metal grade silicon. Therefore, thermodynamic analysis can predict what the steady state is. When argon (Ar) and hydrogen (H ₂ ) containing water vapor are injected into the container containing the liquid metal silicon, the liquid metal impurities in the liquid state and the liquid impurities in the silicon and the vapor of the blowing gas are blown. Si-BPH ₂ O-Ar system containing (H ₂ O), argon (Ar), hydrogen (H ₂ ) can be used to optimize the thermochemical reactions by minimizing Gibbs free energy and to calculate thermodynamic calculations. .

For example, the liquid impurity boron (B) in the liquid state of the metal-grade silicon is reacted with H (g) and SiO (g) to form an HBO (g). That is, boron (B) becomes HBO ( g ) as a result of the reaction and is removed from the liquid silicon (Si).

Boron (B) becomes HBO ( g ) and HBO ₂ ( g ), which are thermodynamically stable, and are removed from liquid silicon (Si).

Phosphorus (P) is removed from the liquid silicon (Si) as PO ( g ), which is in a thermodynamically stable state by reacting with a blowing gas.

Purification method using slag flocculant as impurities in metal grade silicon

Impurities that are not vaporized among the impurities in the metallic silicon are Na-Ca-K-Al- using slag flocculant as sodium (Na), calcium (Ca), potassium (K), and aluminum (Al) as impurities in the metallic silicon. The thermal chemistry of the Si-O system is optimized to react with impurities in the metal-grade silicon to form nonvolatile materials. Impurities in metallic silicon include fluorine (F), aluminum (Al), sulfur (S), calcium (Ca), gallium (Ga), germanium (Ge), selenium (Sr), lithium (Li), and sodium. (Na), magnesium (Mg), chlorine (Cl), potassium (K), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), rubidium (Rb), etc. This slag phase is formed.

Further purification process proceeds with simultaneous reaction

Additional purification processes prior to directional solidification promote reactivity as a simultaneous process, rather than as individual independent processes, and tying up residual impurities in the liquid metal-grade silicon. For example, argon (Ar) and hydrogen (H ₂ ) containing water vapor are blown into the vessel to remove the oxidation of impurities in the molten metal grade silicon, particularly boron (B) and phosphorus (P), which have high segregation coefficients.

Impurity boron (B) in the molten metal grade silicon becomes HBO ( g ) and is removed from the liquid silicon (Si). The impurity phosphorus (P) in the molten metal grade silicon becomes PO ( g ) which is thermodynamically stable and is removed from the liquid silicon (Si).

In addition, the thermal chemical reaction of Na-Ca-K-Al-Si-O system was carried out using sodium (Na), calcium (Ca), potassium (K), and aluminum (Al) as slag flocculants. Optimized to react with impurities in the metal-grade silicon to form a nonvolatile slag phase, which is removed during evaporation.

Directional solidification

Furnace used to manufacture the high purity silicon for solar cells of the present invention is a modification of the one-way solidification device for the silicon, once the further purification process is completed in the furnace (furnace), the one-way solidification proceeds in the same furnace continuously silicon Purify.

One-way solidification can remove most impurities with low segregation coefficients in metallic silicon. The purification method by unidirectional coagulation utilizes an equilibrium diagram established between the silicon to be purified and the impurity element to be removed. The impurity element is discharged from the solid phase into the liquid phase during the solidification of the silicon to be purified and concentrated in the liquid phase. Since the concentration of the impurity element is concentrated in the solidified portion, cutting and destroying the enrichment portion of the impurity element enables high purity silicon to be obtained.

1 is a cross-sectional view of a furnace used to make high purity silicon for solar cells.

Claims

The metal-grade silicon is placed in a pressure-reduced vessel surrounded by a heater, and the metal-grade silicon in the container is melted by the heater to a liquid state, and then argon gas and hydrogen gas containing water vapor are blown into the liquid metal-grade silicon. To optimize the thermochemical reaction of the Si-BPH ₂ O-Ar system to remove the boron (B) and phosphorus (P) in the liquid state of the metal-grade silicon with gaseous oxides HBO and PO and simultaneously Another impurity is a thermal chemical reaction of Na-Ca-K-Al-Si-O system using impurity sodium (Na), calcium (Ca), potassium (K), aluminum (Al) as slag flocculant in the metal-grade silicon. Optimization to remove the other impurities to remove the impurities in the metal-grade silicon, and then to unidirectionally solidify the metal-grade silicon in the liquid state in the container to reduce the metal-grade silicon with a purity of 6N A method of producing a high-purity silicon for solar cells, characterized in that for purifying the high purity silicon.

A method for producing high purity silicon for solar cells by refining metal grade silicon, wherein the metal grade silicon is melted to form a liquid state. Purification to remove impurity boron (B) with HBO ( g ) by blowing argon gas containing water vapor and hydrogen gas into the metallic silicon in a liquid state to remove boron (B) having a segregation coefficient of 0.8. After the process

A method for producing high purity silicon for solar cells, characterized in that the boron content of the silicon is refined to 0.3 mass ppm or less by unidirectional solidification of the metal grade silicon.

The method of manufacturing high purity silicon for solar cells according to claim 2, wherein the purification step and the one-way solidification are continuously purified in the same furnace.