CN101555015B - Purifying method and device for removing boron from polysilicon - Google Patents

Abstract

A boron removal and purification method and device for polysilicon relate to polysilicon. Provided is a method and device for boron removal and purification of polysilicon with low cost, simple process and suitable for industrial promotion. The boron removal and purification device for polysilicon is equipped with a vacuum system, an intermediate frequency induction melting system, a secondary feeding device, a multi-hole rotary nozzle and a graphite mold for casting. Pre-melt the slagging agent, and put the obtained slag into the feeding bin; put the metal silicon into the graphite crucible, vacuumize, connect the power supply of the intermediate frequency induction coil, heat and melt the metal silicon, keep the silicon liquid at 1500-1800 ° C, and lower the porous rotary nozzle Preheat above the surface of the silicon liquid, pass the reaction gas; rotate the feeding bin, add the slagging agent, lower the porous rotary nozzle into the graphite crucible, and start the rotary blade; after the ventilation and slagging is completed, close the rotary blade, and raise the porous rotary Nozzle, turn off the gas source, pour the silicon liquid into the graphite mold and let it stand still, take out the silicon ingot after cooling, remove the impurity-enriched part, and polycrystalline silicon ingot.

Description

A boron removal and purification method and device for polysilicon

technical field

The invention relates to polysilicon, in particular to a method and device for boron removal and purification of polysilicon by metallurgy.

Background technique

The energy crisis and the pollution of the environment by traditional energy have become the main restrictive factors for the development of society and national economy. In order to maintain sustainable development, countries all over the world are actively adjusting their energy structure and vigorously developing renewable energy. Polycrystalline silicon solar cells have become a hot spot of global concern. The process of preparing high-purity polysilicon by using the improved Siemens method is relatively complicated, and the investment cost is high. Using it to prepare solar cells will greatly increase the price of the cell. The process of purifying polysilicon by metallurgy is relatively simple, the cost is low, and the pollution to the environment is relatively small, which has become the main development direction of solar-grade polysilicon.

Industrial silicon is an important raw material for the production of solar-grade polysilicon, but its purity is around 2N, and it often needs to be purified to remove impurity elements, such as Al, Ca, Fe, C, P, B, etc., especially P, B, etc. Metal impurities. P and B are the most difficult to remove in polycrystalline silicon materials, because the segregation coefficients of P and B in Si are 0.35 and 0.8, respectively, which are much higher than metal elements (the segregation coefficient of metal elements in silicon is generally: 10 ^-2 ~10 ^-7 order of magnitude), so, in the conventional directional solidification purification process, when silicon is cooled and solidified from liquid, there are still a lot of P and B staying in the solid phase, and the purification effect is poor.

For P impurities, the most effective way to remove P is to use vacuum to remove phosphorus by utilizing the characteristics that the vapor pressure of P under vacuum increases rapidly with the increase of temperature. For example, US Pat. No. 5,254,300 discloses a method in which molten silicon is refined under reduced pressure so that P enters the gas phase and is removed by volatilization. For B impurities, for example, at 1823K, the vapor pressure of silicon is 0.40 Pa, and the saturated vapor pressure of B is 6.78×10 ^-7 Pa, which is far lower than that of silicon. Therefore, B cannot be removed by vacuum smelting.

In the paper "Refining of Si by the solidification of Si-Al melt with electromagnetic force" (ISIJ International, Vol.45(2005), No.7, pp.967～971), Kazuki Morita et al. of the University of Tokyo proposed that the electric field effect According to the method of solidifying and refining silicon from Si-Al alloy melt, and from theoretical calculation and experimental measurement, it is concluded that the segregation coefficient of B in Si-Al alloy melt has a relatively large decrease. And in another paper "Boron removal by titanium addition in solidification refining of silicon with Si-Al melt" (Takeshi Yoshikawa, Kentaro Arimura, Kazuki Morita, Metallurgical and Materials Transactions B, Volume 36, Number 6, 837～842, 2005) It is proposed that adding Ti element in Si-Al alloy melt can form TiB ₂ precipitation. US Patents US4256717 and US4312848 also disclose the use of similar separation and crystallization methods to add alloy elements to remove B impurities in polysilicon. However, the above methods still need to be studied in terms of how to separate Si and Al and realize industrial production. US Patent US20060123947 uses electron beam vacuum smelting to reduce the B impurity in polysilicon from 55ppmw to 25ppmw. U.S. Patent No. 5,182,091 and papers such as Tomonori Kumagai (Tomonori Kumagai et al.Removal of boron from metallic-grade silicon by applying the plasma treatment "ISIJ International, 1992, 32 (5), 630-634) all disclose a method for melting The method of applying plasma on the silicon surface has a good effect of removing B, but the above process consumes a lot of power, requires high equipment, and is expensive.

At present, the low-cost metallurgical method for removing B mainly utilizes the reaction gas and slag to react with B in the silicon liquid, and the reaction product will be discharged from the system in the form of B-containing gas, such as HBO ₂ , or form boron oxide, such as BO _1.5 enters the slag system and is removed through slag-gold separation.

US Patent US20070180949 mentions a method of blowing a reaction gas composed of Ar, H ₂ , H ₂ O and O ₂ from the bottom of the silicon liquid to oxidize and remove boron, B can be reduced from 25ppmw to 5ppmw. US Patent US60844372 uses natural gas flames with different oxygen ratios and feeds a small amount of Ar, H ₂ and H ₂ O mixed gas to reduce B from 8.9ppmw to 3.6ppmw. U.S. Patent No. 6,368,403 points out that the reaction gas for removing B is mainly a mixed gas composed of inert gases such as Ar and O ₂ .

Tanahashi et al. (Tanahashi et al. Distribution behavior of boron between SiO ₂ -saturated NaO _0.5 -CaO-SiO ₂ flux-molten silicon, Journal of the Mining and Materials, 2002, 118(7): 497-505) proposed to use Na ₂ O-CaO- _SiO2 is the reaction slag system, and the dispersion coefficient of B (the content of B in the slag system/the content of B in the silicon liquid) can reach up to 3.5. The B content can be reduced to 0.4ppmw at most.

Japanese patent JP2851257 also discloses a method of continuously adding slagging agent to molten silicon. At 1500°C, SiO ₂ and Na ₂ CO ₃ are added twice, and B drops from 12ppmw to 0.29ppmw.

To sum up, there are certain deficiencies in the main technological methods at present. First, the removal effect of B is difficult to meet the requirements of solar-grade polysilicon. Secondly, there are certain limitations in the way of introducing gas, and the ventilation parts are easily corroded or damaged. And considering the viscosity of the silicon liquid, the diffusion effect and reaction degree of the gas are not ideal. Moreover, part of the oxidizing gas will react with silicon at high temperature, resulting in unnecessary loss of silicon. In addition, for ordinary slagging reactions, according to K.Suzuki and N.Sano's paper (Thermodynamics for removal of boron from metallic silicon by flux treatment, 10 ^th European photovoltaic solar energy conference, 273-275, 1991), due to the The dispersion coefficient is very small. If you want to obtain a good B removal effect, you must increase the amount of slagging agent and repeat the smelting, which obviously does not meet the requirements of low-cost industrial production. For example, U.S. Patent No. 5,788,945 uses a CaO-SiO ₂ slag system with a B dispersion coefficient of up to 2, and the slag-gold ratio still needs to be maintained at 1:1. If the slag-gold ratio is too high, it is not suitable in terms of economic cost.

Except above method, the technology of chlorination method is mature, and purity is high, discloses a kind of method that feeds HCl as U.S. Patent US4298423, but there is bigger environmental and safety problem.

In addition, a low-cost smelting method also includes molten salt electrolysis, which uses industrial silicon as a raw material, adds molten halide salts, heats and electrolyzes, and forms high-purity silicon deposits on the cathode. However, the conductive material performance of this process is poor, and the deposition rate is limited.

Contents of the invention

The object of the present invention is to provide a method and device for boron removal and purification of solar-grade polysilicon that are low-cost, simple in process and suitable for industrialization in view of the limitations of existing methods for removing B impurities in polysilicon.

The technical scheme of the present invention is to adopt the boron removal method of the metallurgical method, to oxidize the boron by blowing in the oxidizing gas, or to add a slag aid to make the boron form a multi-element slag phase to remove the boron impurities in the silicon.

The polysilicon boron removal and purification device of the present invention is equipped with a vacuum system, an intermediate frequency induction melting system, a secondary feeding device, a porous rotary nozzle and a graphite mold for casting.

The vacuum system is equipped with a mechanical rotary vane pump and a Roots pump. The intermediate frequency induction melting system is equipped with an induction coil and a graphite crucible. The induction coil is located outside the graphite crucible. The secondary feeding device is located above the graphite crucible. The feeding bin and the rotating mechanism, the porous rotary nozzle is set above the graphite crucible, the porous rotary nozzle is provided with rotating blades, and the shaft of the rotating blade is provided with a vent pipe for injecting reaction gas, the rotating blades and the vent pipe are symmetrically distributed, and the bottom end of the vent pipe It is connected with the top of the rotating blade, and the gas is blown in through the nozzle hole arranged between the rotating blade shaft and the rotating blade.

The graphite mold for casting can be provided with 4 pieces of graphite flakes. Rotary blade preferably establishes 6 pieces.

The multi-hole rotary nozzle can adopt a liftable multi-hole rotary nozzle.

The boron-removing purification method of polysilicon of the present invention comprises the following steps:

1) Metal silicon with a purity of 99% (2N) is used as a raw material;

2) pre-melting the slagging agent, and loading the obtained slag into the feeding bin in the secondary feeding device in equal amounts;

3) Put the raw material silicon metal into the graphite crucible, start the mechanical rotary vane pump and Roots pump to evacuate, when the vacuum degree reaches below 100Pa, turn on the power supply of the intermediate frequency induction coil, and heat and melt the metal silicon in the graphite crucible;

4) When the silicon is completely melted, increase the power of the power supply to keep the temperature of the silicon liquid at 1500-1800°C, lower the porous rotary nozzle above the surface of the silicon liquid for preheating, and inject reaction gas to blow on the surface;

5) Rotate the feeding bin, add the pre-melted slagging agent to the silicon liquid in batches, lower the porous rotary nozzle into the graphite crucible, and start the rotary blades to ventilate while stirring;

6) After the ventilation and slagging is completed, close the rotating blade, raise the porous rotary nozzle, and turn off the gas source, pour the silicon liquid into the graphite mold for casting, let it stand, and take out the silicon ingot after cooling to remove the enrichment of impurities at the head and tail Partly, polysilicon ingots after boron removal and purification are obtained.

It can measure the boron impurity content before and after boron removal and purification.

The metal silicon can be block or powder.

The slagging agent can be alkali metal-based oxides, alkali metal-based fluorides, alkali metal carbonates, BaCO ₃ , Ba(OH) ₂ and SiO ₂ , wherein the content of SiO ₂ does not exceed 30%. After pre-melting, the slagging agent can be added into the silicon liquid in 4 batches, and the time interval between each addition is preferably 15-20 minutes.

The power of the medium frequency induction heating power supply can be controlled at 20-50kW.

The preheating time of the porous rotary nozzle above the surface of the silicon liquid is preferably 5-10 minutes, inserted into the graphite crucible, the distance from the bottom is preferably 20-30mm, and the rotation speed is preferably 100-500rpm/min.

The reaction gas introduced can be a mixed gas of water vapor and argon, the content of water vapor should not exceed 1.5%, the gas flow rate can be 6-24L/min, preferably 18-24L/min, and the aeration time can be 60 ～120min, preferably 90～120min. In the process of aeration and slagging, the vacuum degree should preferably be kept at 100-500Pa.

The key technology of the present invention is to introduce a certain oxidizing atmosphere under negative pressure to make B active oxidize to form volatile compounds, and make B form a multi-component slag phase by adding a slag aid to facilitate the separation of slag and gold. The combination of slagging can achieve the purpose of effectively removing B. The specific method of the invention is to melt the raw metal silicon by induction heating the graphite crucible, and to feed oxidizing gas and add slagging agent to remove B under the condition of low vacuum and high temperature. Among them, the slag is added to the silicon liquid in batches according to a certain time interval in the form of pre-melting, and the mixed gas of water vapor and argon is blown from the porous rotary nozzle at a certain ratio and flow rate, and the silicon liquid is stirred by the rotating parts to make the molten silicon melt. The slag and reaction gas are fully and evenly dispersed in the silicon liquid.

The selection of the slagging agent used in the present invention includes:

1) Provide a lower melting temperature to keep the molten state during the slagging process;

2) There is a certain difference between the density and the density of metal silicon, so that the generated slag can float on the surface of liquid silicon or sink to the bottom, so as to facilitate the separation of slag and gold;

3) Provide better liquidity;

4) It can improve the dispersion coefficient of B in the slag system;

5) Provide a sufficient amount of oxidizing agent to fully react with B in the silicon liquid;

6) Can be effectively combined with the ventilation response;

7) Avoid introducing too many impurities.

According to K.Suzuki and N.Sano's paper "Thermodynamics of boron in a silicon melt" (Metallurgical and Materials Transactions B, Volume 25B, 1994), B and slagging agents, such as SiO _2, can react as follows:

B(l in Si)+3/4(SiO ₂ )＝(BO _1.5 )+3/4 Si(l)

Among them, BO _1.5 tends to be more stable in the alkaline slag system. Furthermore, according to the paper "Estimation of water vapor solubility in molten silicates by quadratic formalism based on the regular solution model" (Shiro Ban-Ya, Mitsutaka Hino, Tetsuya Nagasaka, ISIJ International, Vol 33, No 1, 12-19, 1993) According to the calculation, the introduction of H ₂ O into the highly alkaline slag can effectively increase the concentration of OH ^- ions and free oxygen in the melt, and provide more favorable conditions for the formation of BOH volatilization and the formation of B ₂ O ₃ into the slag phase. conditions of.

Therefore, the slag system selected in the present invention is mainly composed of alkali metal-based oxides, alkali metal carbonates and _SiO2 , etc., and the ratio of alkali metal oxides to _SiO2 is controlled to ensure that the slag system is alkaline. At the same time, BaCO ₃ , Ba(OH) ₂ , CaF ₂ etc. can be added to adjust the basicity, melting point, viscosity and density of the system.

The selection of the reaction gas in the present invention, from the above analysis, the gas used for the refining reaction blown in the present invention contains a small amount of H ₂ O, and an inert gas such as Ar which does not react substantially with silicon is used as the carrier gas.

By adopting the boron removal and purification method of the present invention, the B content can be reduced to 0.1 ppmw at most, which meets the purity requirement of solar-grade polysilicon.

Compared with the existing methods and devices for removing B from solar-grade polysilicon, the present invention carries out gas blowing and slagging at the same time, and through stirring, accelerates the reaction to oxidize the B impurities in liquid silicon, and the generated boron oxides, on the one hand It can enter into the slag system, and after reaching thermodynamic equilibrium, it can be cooled to realize the separation of slag and gold; on the other hand, it can also be discharged from the system in the form of boron-containing gas, and the effect of B removal can be achieved. The adopted movable multi-hole rotary nozzle applies the rotary blowing method in the aluminum industry to the silicon purification process, which can greatly increase the air flow without splashing the silicon liquid. At the same time, under the strong agitation of the rotating blades, , can significantly improve the dispersion degree of reaction gas and slagging agent, make full contact with silicon liquid, and increase the effect of B removal. There is no relevant report in this aspect in China. The above process is simple to operate, and the device can be modified from a traditional intermediate frequency furnace. The cost is low, the environmental pollution is small, and it is convenient for industrialization and promotion, and has a considerable market prospect.

Description of drawings

Fig. 1 is a schematic structural diagram of a boron removal and purification device for solar-grade polycrystalline silicon according to an embodiment of the present invention.

Fig. 2 is a structural schematic diagram of a multi-hole rotary nozzle of a boron removal and purification device for solar-grade polysilicon according to an embodiment of the present invention.

Detailed ways

Referring to Fig. 1 and 2, polysilicon of the present invention removes boron and purifies device and is provided with vacuum system (not drawn among the figure), medium frequency induction smelting system 1, secondary feeding device 4, porous rotary nozzle 5 and pouring graphite mold (in the figure) not shown).

The vacuum system is equipped with a mechanical rotary vane pump and a Roots pump. The intermediate frequency induction melting system 1 is equipped with an induction coil 2 and a graphite crucible 3. The induction coil 2 is located outside the graphite crucible 3, and the secondary feeding device 4 is located above the graphite crucible 3. , The secondary feeding device 4 is provided with 4 feeding bins and a rotating mechanism, and batch feeding can be realized through the rotating mechanism. The porous rotary nozzle 5 is arranged above the graphite crucible 3. The porous rotary nozzle 5 is provided with a rotary vane 7, and the rotary vane shaft is provided with a vent pipe 6 for injecting reaction gas. The rotary vane 7 and the vent pipe 6 are symmetrically distributed. The bottom end is connected with the top of the rotating blade 7, and the gas is blown in through the nozzle hole 8 arranged between the rotating blade shaft and the rotating blade.

The graphite mold for casting can be provided with 4 pieces of graphite flakes. Rotary blade preferably establishes 6 pieces.

The multi-hole rotary nozzle 5 can adopt a liftable multi-hole rotary nozzle.

Several examples of boron removal and purification methods for solar-grade polysilicon according to the present invention are given below.

Example 1

1) Weigh 10kg of raw metal silicon with a B concentration of about 10ppmw.

2) Mix CaO, CaF ₂ , BaO and SiO ₂ powders in a certain proportion as a slagging agent, so that the composition ratio of CaO, CaF ₂ , BaO and SiO ₂ is 60:9:6:25. The weight ratio of the slagging agent to the silicon raw material is 1.5:10 (the slag-gold ratio is 0.15), that is, 1.5 kg.

3) After pre-melting the slagging agent, the obtained slag is loaded into four feeding bins in the secondary feeding device in equal amounts.

4) Put the raw metal silicon into the graphite crucible, start the mechanical rotary vane pump and the Roots pump to evacuate, when the vacuum reaches 100Pa, turn on the power supply of the intermediate frequency induction coil, the power is 25kw, until the silicon is completely melted.

5) Increase the power supply to 30kw, make the temperature of the silicon liquid reach 1600°C, lower the porous rotary nozzle above the surface of the silicon liquid to preheat for 10 minutes, and feed 99.5% Ar+0.5% H ₂ O, the content of H ₂ O can be determined by the humidity The meter is controlled and the surface is blown.

6) Rotate the feeding bin, add the pre-melted slagging agent into the silicon liquid in batches, and the time interval between each addition is 15 minutes. Lower the porous rotary nozzle to about 30mm from the bottom of the graphite crucible, the ventilation rate is 12L/min, the ventilation time is 60min, and the rotation speed is 200rpm.

7) After the aeration and slagging is completed, turn off the rotating blade, raise the multi-hole rotating nozzle, and turn off the gas source. Pour the silicon liquid into a graphite mold for casting, let it stand, take out the silicon ingot after cooling, remove 1/10 of the head and tail parts, and measure the B content in the polysilicon ingot by secondary ion mass spectrometry (SIMS) to be 0.52ppmw.

Example 2

Technological process is with embodiment 1. The weight ratio of the slagging agent to the raw silicon is 3:10 (the slag-gold ratio is 0.3), that is, 3kg. After the silicon is completely melted, increase the power supply to 35kw to make the temperature of the silicon liquid reach 1650°C, lower the porous rotary nozzle above the surface of the silicon liquid to preheat for 5 minutes, and inject 98.5% Ar+1.5% H ₂ O to blow the surface gas. Rotate the feeding bin, add the pre-melted slagging agent to the silicon liquid in batches, and the time interval between each addition is 20 minutes. Lower the porous rotary nozzle to about 30mm from the bottom of the graphite crucible, the ventilation rate is 18L/min, the ventilation time is 90min, and the rotation speed is 300rpm.

Pour the silicon liquid into the graphite mold for casting, let it stand still, take out the silicon ingot after cooling, remove 1/10 of the head and tail parts, and measure the B content in the polysilicon ingot by secondary ion mass spectrometry (SIMS) to be 0.34ppmw.

Example 3

Technological process is with embodiment 1. Mix CaCO ₃ , CaF ₂ , Ba(OH) ₂ , and SiO ₂ powders in a certain proportion as a slagging agent, so that the composition ratio of CaCO ₃ , CaF ₂ , Ba(OH) ₂ , and SiO ₂ is 55:7:8: 30. The weight ratio of the slagging agent to the raw silicon is 3:10 (the slag-gold ratio is 0.3), that is, 3kg. After the silicon is completely melted, increase the power supply to 40kw to make the temperature of the silicon liquid reach 1700°C, lower the porous rotary nozzle above the surface of the silicon liquid to preheat for 5 minutes, and inject 99.25% Ar+0.75% H ₂ O to blow the surface gas. Rotate the feeding bin, add the pre-melted slagging agent to the silicon liquid in batches, and the time interval between each addition is 20 minutes. Lower the porous rotary nozzle to about 20mm from the bottom of the graphite crucible, the ventilation rate is 24L/min, the ventilation time is 120min, and the rotation speed is 450rpm. Pour the silicon liquid into the graphite mold for casting, let it stand still, take out the silicon ingot after cooling, remove 1/10 of the head and tail parts, and measure the B content in the polysilicon ingot by secondary ion mass spectrometry (SIMS) to 0.11ppmw.

Example 4

Technological process is with embodiment 1. Metal silicon raw material 50kg, mix CaO, CaF ₂ , SiO ₂ powder in a certain proportion as a slagging agent, so that the composition ratio of CaO, CaF ₂ , SiO ₂ is 60:10:30. The weight ratio of the slagging agent to the silicon raw material is 3:10 (the slag-gold ratio is 0.3), that is, 15kg. After the silicon is completely melted, increase the power supply to 45kw to make the temperature of the silicon liquid reach 1750°C, lower the porous rotary nozzle above the surface of the silicon liquid to preheat for 5 minutes, and inject 99% Ar+1% H ₂ O to blow the surface gas. Rotate the feeding bin, add the pre-melted slagging agent to the silicon liquid in batches, and the time interval between each addition is 20 minutes. Lower the porous rotary nozzle to about 20mm from the bottom of the graphite crucible, the ventilation rate is 24L/min, the ventilation time is 100min, and the rotation speed is 500rpm. Pour the silicon liquid into the graphite mold for casting, let it stand still, take out the silicon ingot after cooling, remove 1/10 of the head and tail parts, and measure the B content in the polysilicon ingot by secondary ion mass spectrometry (SIMS) to be 0.45ppmw.

Example 5

Technological process is with embodiment 1. Mix Ca(OH) ₂ , CaF ₂ , Ba(OH) ₂ , and SiO ₂ powders in a certain proportion as a slagging agent, so that the composition ratio of Ca(OH) ₂ , CaF ₂ , Ba(OH) ₂ , and SiO ₂ is 52:7:8:33. The weight ratio of the slagging agent to the raw silicon is 3:10 (the slag-gold ratio is 0.3), that is, 3kg. After the silicon is completely melted, increase the power supply to 50kw to make the temperature of the silicon liquid reach 1800°C, lower the porous rotary nozzle above the surface of the silicon liquid to preheat for 5 minutes, and inject 99.5% Ar+0.5% H ₂ O to blow the surface gas. Rotate the feeding bin, add the pre-melted slagging agent to the silicon liquid in batches, and the time interval between each addition is 20 minutes. Lower the porous rotary nozzle to about 20mm from the bottom of the graphite crucible, the ventilation rate is 20L/min, the ventilation time is 120min, and the rotation speed is 500rpm. Pour the silicon liquid into the graphite mold for casting, let it stand, take out the silicon ingot after cooling, remove 1/10 of the head and tail parts, and measure the B content in the polysilicon ingot by secondary ion mass spectrometer (SIMS) to be 0.22ppmw.

Comparative example 1

Except that no slagging agent was added, the treatment was carried out for 2 hours under similar conditions as in Example 3, and the measured B content after smelting was 3.95 ppmw.

Comparative example 2

Except that no oxidizing gas was introduced, the treatment was carried out for 2 hours under similar conditions as in Example 3, and the B content after smelting was measured to be 1.71 ppmw.

Comparative example 3

Except that the rotating blades were not rotated and stirred, the treatment was carried out for 1 h under similar conditions as in Example 3, and the measured B content after smelting was 1.17 ppmw.

Comparative example 4

Except that the slagging agent is not pre-melted, and is directly mixed and added to the molten silicon at one time, the treatment is carried out for 1 hour under similar conditions as in Example 3, and the measured B content after smelting is 0.99ppmw.

Claims (6)

1. polysilicon removes the boron purifying plant, it is characterized in that being provided with vacuum system, Medium frequency induction smelting system, secondary charging device, porous swivel nozzle and cast graphite jig; Vacuum system is provided with mechanical sliding vane rotary pump and lobe pump, the Medium frequency induction smelting system is provided with ruhmkorff coil and plumbago crucible, ruhmkorff coil is located at the outside of plumbago crucible, the secondary charging device is located at the plumbago crucible top, the secondary charging device is provided with and adds feed bin and rotating mechanism, the porous swivel nozzle is located at the plumbago crucible top, the porous swivel nozzle is provided with rotating paddle, be provided with the ventpipe that is used to inject reactant gases in the pivoting leaf bobbin, rotating paddle and ventpipe are symmetrically distributed, the bottom of ventpipe is connected with the top of rotating paddle, and gas is blown into by the spray orifice of being located between pivoting leaf bobbin and the rotating paddle;

Described cast is provided with 4 graphite flakes with graphite jig;

Described rotating paddle is established 6;

Described porous swivel nozzle adopts liftable porous swivel nozzle.

2. the boron-removing purification method of a polysilicon is characterized in that adopting according to claim 1 that polysilicon removes the boron purifying plant, and described boron-removing purification method may further comprise the steps:

1) selecting purity for use is that 99% Pure Silicon Metal is a raw material;

2) with the slag former fritting, the gained slag equivalent feed bin that adds in the secondary charging device of packing into;

3) feed metal silicon is put into plumbago crucible, start mechanical sliding vane rotary pump and lobe pump and vacuumize,, connect the Medium frequency induction coil power, the Pure Silicon Metal in the heat fused plumbago crucible when vacuum tightness reaches 100Pa when following;

4) after silicon all melts, improve power, make the silicon liquid temp remain on 1500～1800 ℃, the porous swivel nozzle is reduced to the surface preheating of silicon liquid, and feed reactant gases, carry out the surface and blow;

5) rotation adds feed bin, adds the slag former of fritting in silicon liquid in batches, and the porous swivel nozzle is reduced in the plumbago crucible, and start rotating paddle, stir on one side ventilation on one side;

6) after slag making to be ventilated is finished, close rotating paddle, rise the porous swivel nozzle, and close source of the gas, pour silicon liquid into cast with in the graphite jig, leave standstill, silicon ingot is taken out in the cooling back, removes impurity enriched part end to end, obtains removing the polycrystal silicon ingot after boron is purified.

3. the boron-removing purification method of a kind of polysilicon as claimed in claim 2 is characterized in that described Pure Silicon Metal is bulk or powdery.

4. the boron-removing purification method of a kind of polysilicon as claimed in claim 2 is characterized in that slag former through fritting, divides 4 batches to add in the silicon liquid, and each timed interval that adds is 15～20min.

5. the boron-removing purification method of a kind of polysilicon as claimed in claim 2, it is characterized in that the porous swivel nozzle is 5～10min in the time of silicon liquid surface preheating, after reducing in the plumbago crucible, be 20～30mm apart from the bottom, speed of rotation is 100～500rpm/min.

6. the boron-removing purification method of a kind of polysilicon as claimed in claim 2 is characterized in that the reactant gases that feeds is the mixed gas of water vapour and argon gas, and the content of water vapour is no more than 1.5%.

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