A kind of a refining unit of HIGH-PURITY SILICON and method thereof
Technical field
The present invention relates to a kind of a refining unit and method thereof of silicon, especially relate to a kind of a refining unit and method thereof of HIGH-PURITY SILICON.
Background technology
Sun power is the abundant clean reproducible energy of a kind of energy storage, and solar electrical energy generation will become the important channel of not solving energy dilemma and environmental problem, obtain the generally attention of countries in the world.In global fast development, the dead meal of electronic-grade silicon can not meet the demands far away along with photovoltaic industry, and the technology of chemical method purifying polycrystalline silicon because its productive rate is low, large, the pollution of cost of investment and security problems hindered the development of photovoltaic industry.Metallurgy method is considered to can effectively reduce the technology of solar-grade polysilicon production cost because of characteristics such as it are with short production cycle, pollution is little, cost is low, obtained the extensive attention of industry and greatly developed.
Impurity in industrial silicon mainly contains nonmetallic impurity and metallic impurity: (1) nonmetallic impurity is mainly C, O, B, P, wherein C, O easily with silicon liquid in Si formation SiC and SiO
2Separate and remove, but B, P are difficult to remove; (2) metallic impurity are mainly Fe, Al, Ca etc., and the segregation coefficient of metallic impurity in Si is less, can the method by directional freeze remove, but the segregation coefficient of B, P large (0.8,0.35) be difficult to remove by directional freeze.Although B, P impurity difficulty are removed, must be removed to certain limit, this is because B, P are two most important elements that affect solar cell properties.Therefore, the effective ways of exploring except B, P are one of main study hotspots of metallurgy method purifying polycrystalline silicon.
For P impurity,, because its saturated vapor pressure at high temperature is far longer than silicon,, by the method for vacuum melting, under certain high vacuum, the volatilization such as P impurity is entered in gas phase, can obtain preferably except the P effect.The researchist utilizes this physical properties of P impurity to carry out large quantity research both at home and abroad.The people such as Yuge [N Yuge et al.Removal of Phosphorus, Aluminum and Calcium by Evaporation in Molten Silicon[J] .J.Japan Inst.Metals, 1997,61 (10): 1086-1093.] be that 1642 ℃, vacuum tightness are 8.0 * 10 in temperature
-3Pa~3.6 * 10
-2Under the condition of Pa, the phosphorus content in silicon is reduced to below 0.1ppmw from 20~27ppmw.In addition, they have also found that in silicon, the content of phosphorus reduces gradually along with the increase of smelting time, and smelting temperature is higher, and the removal effect of P is better.The people such as Zheng Songsheng [S.S Zheng, et al.Elimination of phosphorus vaporizing from molten silicon at a finite reduced pressure[J] .Transactions of Nonferrous Metals Society of China, 2011,21 (3): 697-702.] at first electronic-grade silicon is carried out the P doping, then under 1600 ℃, 0.6 melting 1h under the vacuum tightness of~0.8Pa, can be down to 10ppmw from 460ppmw with the P impurity in the Si-P alloy.But in suitability for industrialized production, the experiment condition that obtain the high temperature high vacuum has very high requirement to the Design and manufacture of equipment, and separate unit is long working cycle, is difficult for accomplishing scale production.
At present, in the removal industrial silicon, the main method of B impurity is slag refining etc.Slag refining is to utilize some impurity and the slag former generation chemical reaction that adds in silicon melt in silicon melt, form slag mutually after because the difference of density floats to the surface of silicon melt or sinks to the bottom of silicon melt, thereby separate again the effect that reaches purification after solidifying with solid silicon.But also there are some problems in slag refining, and is as large in slag agent usage quantity, and waste residue is difficult to recycling, and unfriendly to environment, the yield of silicon is low etc.
Blowing refining is a kind of effective ways of removing B impurity.The method, by pass into the mixed gas of oxidizing gas and rare gas element in molten silicon, realizes the purification purpose.On the one hand, (generally select O toward the oxidizing gas that passes in the industrial silicon of melting
2, H
2O and CO
2Deng) can make partial impurities in silicon be oxidized to volatile gases to separate with silicon; On the other hand, the rare gas element that passes into (generally selecting Ar) can play the effect of stir silicon liquid, accelerates the mass-and heat-transfer speed of metallurgical melt, promotes diffusion of contaminants, and the silicon melt surface is constantly updated, and improves chemical reaction rate.In the blowing refining process, the B impurity in silicon can react with oxidizing gas, generate volatile gases, and vacuum system is constantly taken foreign gas away, and in silicon melt, the B foreign matter content significantly reduces.The people such as G.Flamant (G.Flamant, et al.Purification of metallurgical grade silicon by a solar process[J] .Solar Energy Materials and Solar Cells, 2006,90 (14): the research of 2099-2106.) carrying out the industrial silicon blowing refining is found, the mixed gas that passes into argon gas and water vapour can obviously reduce the content of B, P, B content is down to 2.1ppmw from 5.7ppmw, and P content is down to 3.2ppmw from 9.4ppmw.
At present, the a refining unit of industrial silicon is generally to adopt carbon tube to insert in silicon liquid to carry out blowing refining, by bath top air feed, gas interacts by the formed supersonic airstream of air gun and molten bath, formed the emulsion of gas-slag-silicon liquid, high temperature reaction zone concentrates on weld pool surface, has caused in molten bath composition and thermograde larger, very inhomogeneous.Simultaneously, fume amount is large, and the silicon loss is more.US Patent No. 20070180949 discloses and a kind ofly from silicon liquid bottom, is blown into by Ar, H
2, H
2O and O
2Remove the method for B in silicon Deng the mixed gas that forms, B content can be down to 5ppmw from 25ppmw.
Blowing refining can obviously reduce B content, and its advantage is that equipment requirements is simple, energy consumption is low, simple to operate.Shortcoming be air flow too conference cause a large amount of oxidations of Si and the spray stove dangerous, air flow is too little again can be because impurity is difficult to effectively contact and affect dust removal rate with gas, so air flow and ventilating mode are individual key issues.
Plasma refining be utilize plasma arc as thermal source melt, a kind of smelting process of refining industrial silicon.Because plasma arc belongs to compression arc, energy height is concentrated, and is the energy of a high heat, high temperature.Plasma melting, except boron just is being based on the ultrahigh-temperature of plasma body, under the oxidizing gas effect, makes the boron active oxidation form volatile small molecules oxide compound and overflows from silicon liquid, thereby reaches the purpose of effective removal B impurity.The people such as Suzuki (K.Suzuki, et al.Removal of boron from metallurgical-grade silicon by applying the plasma treatment[J] .ISIJ International, 1992,32 (5): 630-634.) in the process of the reaction kinetics in research plasma process process and mechanism, find can form BO, B at plasma except temperature B when 2300K is above in the boron process
2O, B
2O
2Deng the gaseous boron oxide compound, wherein the vapour pressure of BO is higher, and B mainly overflows from silicon liquid with the form of BO.
The action of plasma scope is little, and current consumption is large, in commercial application, if directly using plasma heat fused, refining will make high cost.The people such as C.Alemany (C.Alemany, et al.Refining of metallurgical-grade silicon by inductive plasma[J] .Solar Energy Materials and Solar Cells72 (2002): 41 – 48) disclose a kind of method that induction stirring combines with plasma melting, effectively reduced energy consumption.
Under high vacuum environment, industrial silicon P, B impurity can be effectively removed in blowing refining and high-temperature plasma melting.They respectively have relative merits, make it to combine to learn from other's strong points to offset one's weaknesses, and the dephosphorization that greatly improves industrial silicon is except effect of boron.Present method, utilizing blowing refining to remove on the basis of boron, has also been utilized the droplet treatment of silicon melt in the air blowing process, thereby reaches the purpose that enlarges evaporation area removal phosphorus impurities.
Summary of the invention
The object of the invention is to the existing limitation of devices and methods therefor for phosphorus boron impurity in existing removal polysilicon, provide low-cost, efficient, technique is simple and a refining unit of a kind of HIGH-PURITY SILICON of suitable Industry Promotion and method thereof.
The a refining unit of HIGH-PURITY SILICON of the present invention is provided with medium frequency induction melting furnace, lifting device, plasma melting device, porous plug device, vacuum system and cast graphite jig;
Described medium frequency induction melting furnace is provided with bell, plumbago crucible and Medium frequency induction coil, and lifting device is located on bell, and the Medium frequency induction coil is located at the outside of plumbago crucible, is provided with thermal insulation layer between Medium frequency induction coil and plumbago crucible; Described plasma melting device is provided with plasma gun and arc initiation device, and arc initiation device and plasma gun all are fixed on bell, and plasma gun can vertically move, and plasma gun is provided with entrance of cooling water, cooling water outlet and argon gas import; Described porous plug device is provided with porous plug, guide rod and transmission mechanism, porous plug is connected with transmission mechanism, porous plug and transmission mechanism are positioned at the plumbago crucible bottom, guide rod is connected with the porous plug bottom, porous plug is provided with gas pipeline and is used for passing into working gas, the gas pipeline top is provided with air outlet, porous plug can be under transmission mechanism drives VTOL (vertical take off and landing); Described vacuum system is provided with mechanical sliding vane rotary pump and lobe pump, and medium frequency induction melting furnace is connected with mechanical sliding vane rotary pump by lobe pump; Described cast is provided with 4 graphite flakes with graphite jig.
Described thermal insulation layer can adopt thermal insulation fire-resistant mud thermal insulation layer.
The power of described medium frequency induction melting furnace is controlled at 300~500kW.
The power supply of described plasma melting device is controlled at 100~350kW.
Described plumbago crucible capacity can hold 100~500kg silicon material.
Described air outlet can be provided with 4.
The working gas that passes into is the mixed gas of argon gas and water vapour, and in mixed gas, the volume fraction of water vapour is 0~1.5%, and the volume fraction of argon gas is 98.5%~100%, and Ventilation Rate is 20~30L/min.
The time length of blowing refining and plasma melting is 30~60min.
The method of refining of HIGH-PURITY SILICON of the present invention comprises the following steps:
1) selecting low-phosphorous low boron industrial silicon is the silicon material;
2) the silicon material is put into plumbago crucible, close bell, open mechanical pump and lobe pump and vacuumize, then start medium frequency induction melting furnace the silicon material is heated;
3) after the silicon material all melts, improve the medium frequency induction melting furnace power, silicon liquid is incubated at 1600~1850 ℃;
4) start the porous plug device, porous plug rises to apart from 10mm place, plumbago crucible bottom under transmission mechanism drives, pass into working gas by gas pipeline to silicon liquid bottom and carry out melting; Start simultaneously the plasma melting device, first by arc initiation device, carry out striking, after striking is completed, arc initiation device is shifted, then plasma melting is carried out on silicon liquid surface;
5) after blow melting and plasma melting are completed, first close the plasma melting device, porous plug drives and drops to the plumbago crucible bottom at transmission mechanism, keep ventilation in case silicon liquid enters gas passage in this process, close the porous plug device after porous plug is down to the plumbago crucible bottom, stops ventilation;
6) silicon liquid is poured into cast with in graphite jig, standing cooling rear taking-up silicon ingot, obtain the high-purity silicon ingot after dephosphorization removes the boron purification.
In step 1), the purity of described low-phosphorous low boron industrial silicon is 99%, and wherein, the content of boron is 1~2ppmw, and the content of phosphorus is 5~6ppmw.
In step 2) in, the power of described medium frequency induction melting furnace is controlled at 200~300kW.
In step 3), the power of described medium frequency induction melting furnace rises to 300~500kW at silicon liquid holding stage.
In step 4), the power of described plasma melting device is controlled at 100~350kW; Described working gas is the mixed gas of argon gas and water vapour, in mixed gas, the volume fraction of water vapour is 0~1.5%, the volume fraction of argon gas is 98.5%~100%, Ventilation Rate is 20~30L/min, blowing refining and plasma refining process continue 30~60min, and the silicon liquid temp is controlled at 1600~1850 ℃.
Adopt a refining unit and the method thereof of HIGH-PURITY SILICON of the present invention, can make the content of B impurity be down to 0.1ppmw from 2ppmw, P content is reduced to below 0.3ppmw from 6ppmw, meets the requirement of solar-grade polysilicon to the phosphorus boron impurity.
Compare with purifying plant and the method thereof of existing solar-grade polysilicon, the present invention is take special 2N industrial silicon as raw material, adopt the porous plug device carry out blowing refining except boron and make the melt droplet treatment, increase silicon liquid evaporation area, make and have high-volatile P Impurity removal, thereby improved the working gas utilization ratio, and further reduced the content of B impurity in silicon liquid by the plasma melting device.Above technological operation is simple, and device can be transformed by traditional medium frequency induction melting furnace, and cost is low, environmental pollution is little, be convenient to Industry Promotion, has considerable market outlook.
Description of drawings
Fig. 1 is the structural representation of a refining unit embodiment of HIGH-PURITY SILICON of the present invention.
Fig. 2 is the structural representation of porous plug of a refining unit embodiment of HIGH-PURITY SILICON of the present invention.
Fig. 3 is the A-A sectional view of Fig. 2.
In Fig. 1~3, respectively be labeled as: the 1-lifting device; The 2-bell; The 3-thermal insulation layer; The 4-transmission mechanism; The 5-guide rod; The 6-porous plug; The 7-gas pipeline; The 8-plumbago crucible; 9-Medium frequency induction coil; The 10-medium frequency induction melting furnace; The 11-arc initiation device; The 12-plasma gun; The 13-entrance of cooling water; The 14-cooling water outlet; The import of 15-argon gas; The 16-lobe pump; 17-machinery sliding vane rotary pump; The 71-air outlet.
Embodiment
Referring to Fig. 1~3, a refining unit embodiment of HIGH-PURITY SILICON of the present invention is provided with medium frequency induction melting furnace 10, lifting device 1, plasma melting device, porous plug device, vacuum system and cast graphite jig.Described medium frequency induction melting furnace 10 is provided with bell 2, plumbago crucible 8 and Medium frequency induction coil 9, and lifting device 1 is located on bell 2, and Medium frequency induction coil 9 is located at the outside of plumbago crucible 8, is provided with thermal insulation layer 3 between Medium frequency induction coil 9 and plumbago crucible 8; Described plasma melting device is provided with plasma gun 12 and arc initiation device 11, arc initiation device 11 all is fixed on bell 2 with plasma gun 12, plasma gun 12 can vertically move, and plasma gun 12 is provided with entrance of cooling water 13, cooling water outlet 14 and argon gas import 15; Described porous plug device is provided with porous plug 6, guide rod 5 and transmission mechanism 4, porous plug 6 is connected with transmission mechanism 4, porous plug 6 and transmission mechanism 4 are positioned at plumbago crucible 8 bottoms, guide rod 5 is connected with porous plug 6 bottoms, porous plug 6 is provided with gas pipeline 7 and is used for passing into working gas, gas pipeline 7 tops are provided with 4 air outlets 71, porous plug 6 can be under transmission mechanism 4 drives VTOL (vertical take off and landing); Described vacuum system is provided with mechanical sliding vane rotary pump 17 and lobe pump 16, and medium frequency induction melting furnace 10 is connected with mechanical sliding vane rotary pump 17 by lobe pump 16; Described cast is provided with 4 graphite flakes with graphite jig.
Described thermal insulation layer 3 adopts thermal insulation fire-resistant mud thermal insulation layer.
The power of described medium frequency induction melting furnace 10 is controlled at 300~500kW.
The power supply of described plasma melting device is controlled at 100~350kW.
Described plumbago crucible 8 capacity can hold 100~500kg silicon material.
The working gas that passes into is the mixed gas of argon gas and water vapour, and in mixed gas, the volume fraction of water vapour is 0~1.5%, and the volume fraction of argon gas is 98.5%~100%, and Ventilation Rate is 20~30L/min.
The time length of blowing refining and plasma melting is 30~60min.
Below provide embodiments of the invention.
Embodiment 1
1) purity that takes is 99% industrial silicon 300kg, and its boron phosphorus content is respectively 1~2ppmw, 5~6ppmw.
2) the silicon material is put into plumbago crucible, start vacuum system and vacuumize, when vacuum tightness reaches 10Pa, connect the medium frequency induction melting furnace power supply, regulating power, to 300kW, heats the silicon material.
3) improve the medium frequency induction melting furnace power to 350kW, silicon liquid is incubated at 1600 ℃.
4) start porous plug device and plasma melting device, to passing into volume fraction in the porous plug gas pipeline, be respectively 99.5% and 0.5% argon gas and the mixed gas of water vapour, then rise porous plug to air outlet apart from 10mm place, plumbago crucible bottom.Ventilation Rate is 20L/min, and smelting time is 45min, and water vapour content can be controlled by wet bulb thermometer.The power of plasma melting is 150kW.
5) after melting is completed, porous plug is down to crucible bottom, closes porous plug device and plasma melting device.
6) after plasma melting is completed, close the plasma melting installation's power source.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.15ppmw, the content of P is 0.33ppmw.
Embodiment 2
Raw material and technological process are with embodiment 1.Improve the medium frequency induction melting furnace power to 400kW, silicon liquid is incubated at 1700 ℃.Be respectively 99% and 1% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 25L/min, and smelting time is 50min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.12ppmw, the content of P is 0.31ppmw.
Embodiment 3
Raw material and technological process are with embodiment 1.Improve the medium frequency induction melting furnace power to 450kW, silicon liquid is incubated at 1750 ℃.Be respectively 98.5% and 1.5% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 30L/min, and smelting time is 60min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.10ppmw, the content of P is 0.33ppmw.
Embodiment 4
Raw material and technological process are with embodiment 1.Improve the medium frequency induction melting furnace power to 500kW, silicon liquid is incubated at 1800 ℃.Be respectively 98.5% and 1.5% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 30L/min, and smelting time is 60min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.10ppmw, the content of P is 0.30ppmw.
Embodiment 5
Raw material and technological process are with embodiment 1.Improve the medium frequency induction melting furnace power to 500kW, silicon liquid is incubated at 1800 ℃.Be respectively 97.5% and 2.5% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 30L/min, and smelting time is 60min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.11ppmw, the content of P is 0.30ppmw.
Embodiment 6
Technological process is with embodiment 1.Take silicon material 100kg, improve the medium frequency induction melting furnace power to 300kW, silicon liquid is incubated at 1600 ℃.Be respectively 98.5% and 1.5% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 20L/min, and smelting time is 45min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.09ppmw, the content of P is 0.32ppmw.
Embodiment 7
Technological process is with embodiment 1.Take industrial silicon 500kg, improve the medium frequency induction melting furnace power to 500kW, silicon liquid is incubated at 1800 ℃.Be respectively 98.5% and 1.5% argon gas and the mixed gas of water vapour to passing into volume fraction in silicon liquid, Ventilation Rate is 30L/min, and smelting time is 60min.Pour silicon liquid into cast with in graphite jig, standing cooling rear taking-up silicon ingot, remove end to end each 1/10, recording B content in polycrystal silicon ingot by plasma inductance coupling mass spectrograph (ICP-MS) is 0.15ppmw, the content of P is 0.35ppmw.