CN102616787B - Method for removing boron-phosphorus impurities from silicon metal - Google Patents

Method for removing boron-phosphorus impurities from silicon metal Download PDF

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CN102616787B
CN102616787B CN201210078794.4A CN201210078794A CN102616787B CN 102616787 B CN102616787 B CN 102616787B CN 201210078794 A CN201210078794 A CN 201210078794A CN 102616787 B CN102616787 B CN 102616787B
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slag
boron
slag charge
industrial silicon
phosphorus impurities
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CN102616787A (en
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罗学涛
余德钦
林彦旭
方明
卢成浩
李锦堂
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Xiamen University
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Xiamen University
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Abstract

A method for removing boron-phosphorus impurities from silicon metal relates to a silicon metal purifying method. The method includes: firstly, premelting slag charges 2 which are Cao-CaSi2; secondly, pressing slag charges 1 into slag balls, placing part of the slag charges 1 and silicon metal into a crucible, and vacuumizing, starting a medium-frequency induction power source to heat and smelt the materials, wherein the slag charges 1 are SiO2-Na2CO3-CaF2; thirdly, increasing the power of the medium-frequency induction power source to 80kW to 100kW, when the temperature ranges from 1300 DEG C to 1500 DEG C, adding part of slag charges 2 into the crucible, aerating while stirring, continuing to increase the power of the medium-frequency induction power source to 100kW to 120kW, and when the temperature ranges from 1600 DEG C to 1800 DEG C, adding part of slag charges 1 into the crucible, aerating while stirring, lowering the power to 80kW and waiting the temperature to drop; fourthly, repeating the step three; and fifthly, slagging, pouring liquid silicon into a receiving crucible for standing and cooling, taking out silicon ingots, and physically crushing the silicon ingots to obtain purified polycrystalline silicon ingots.

Description

A kind of method of removing boron from industrial silicon phosphorus impurities
Technical field
The present invention relates to a kind of method of purification of industrial silicon, especially relate to a kind of method that adopts hydridization slag practice to remove boron from industrial silicon phosphorus impurities.
Background technology
After 2000, photovoltaic industry presents the trend of an outburst, has totally continued more than 10 year, the about 1787MW of global photovoltaic generation total amount in 2005.Expect the year two thousand fifty, global generating capacity can arrive 18GW.In recent years, the research and development of solar cell are as an important channel of development clean energy, and the raw material that the solar cell over 90% adopts is crystalline silicon, is the waste material from HIGH-PURITY SILICON and electronic-grade silicon, with high costs.In order to meet growing polysilicon demand, develop a kind of method of producing cheaply solar energy polycrystalline silicon very necessary.
At present, produce polysilicon and be mainly divided into two kinds of methods: chemical method and physical metallurgy method.Chemical method is improved Siemens, silane thermal decomposition process and fluidized bed process, but these method investments are large, and energy consumption is high, and process is complicated and wayward, as intermediate product, deals with improperly and will environment be caused to very big pollution.The essence of physical metallurgy method is that silicon material remains unchanged in purification process, and the process such as the metallurgical reaction by impurity, evaporation, fractional condensation in addition separation directly obtains solar-grade polysilicon.Process aspect mainly comprises hydrometallurgy (pickling), slag making, directional freeze, high vacuum melting, plasma oxidation refining, alloy directional purification, fused salt electrolysis etc.
Polycrystalline silicon used for solar battery has stricter restriction to the content of non-metallic element B and P, requires the content of B below 0.5ppm, and the content of P is below 1ppm.In conventional directional freeze, B is relative with P, and other metallic elements have larger segregation coefficient, still can rest in solid phase, cannot realize refining effect.Consider that P has higher vapour pressure, so currently used high vacuum melting has quite significantly effect for removing P, Xiamen University's metallurgical laboratory is by 1600 ℃ of pilot experiments (15kg level), and melting silicon 1h under the vacuum tightness of 0.012~0.035Pa, can be reduced to 0.08ppmw (Zheng Songsheng from 15ppmw by the content of impurity P, old court, Luo Xuetao, the progress of polysilicon metallurgy method dephosphorization, material Leader, 2009,23(10): 11-14).In US Patent No. 20110217225Al, mention and in the process of refining solar energy polycrystalline silicon, add two appropriate calcium silicides, melting under argon atmospher, can make P be reduced to solar level standard, and other impurity are also had to obvious removal effect.
So far, by slag making, removing B is a kind of fairly simple feasible method, slag refining be mainly utilize the thermodynamic stability of B oxide compound in slag high (G is low) and make that impurity can be more crosses be enriched in slag mutually in, thereby realize B from silicon phase transition to slag phase.The people such as Lynch mention by slag making and follow-up techniques and remove B and the P in metalluragical silicon in International Publication No.WO2007/127126, and slag system used is Al 2o 3-SiO 2-CaO-MgO, slag system is played the part of a rinse bath that can dissolve B and P, and whole process is led to N 2, generally, silicon needs deoxidation that the purifying reaction of B and P is carried out, and oxidation refining is carried out subsequently, finally by directional freeze, removes some other impurity, thereby produce, is applicable to polycrystalline silicon used for solar battery.The people such as TEIXEIRA (leandro Augusto Viana TEIXEIRA and Kazuki MORITA, Removal of Boron from Molten Silicon Using CaO-SiO 2based slags, ISIJ International, 2009,49(6): 783-787) with Calucium Silicate powder slag system, inquiring into the removal mechanism of B, thereby obtain some more accurate thermodynamic datas, is mainly for L b(the separation ratio of B) and the activity quotient of boron-oxygen are analyzed, and slag system used is CaO-SiO 2-CaF 2and Na 2o-CaO-SiO 2, result shows BO 1.5activity quotient in 0.3~7.0 scope, Na 2the interpolation of O can increase the separation ratio of boron.The people such as M.Barati of Toronto university adopt quaternary slag system Al 2o 3-CaO-MgO-SiO 2with ternary slag system Al 2o 3-BaO-SiO 2carry out the partition ratio of further investigated impurity element B and P, analyze the basicity and their partition ratio of oxygen gesture joint effect that draw slag system, and these all form relevant with the component of slag system.
Chinese patent CN1016710239 adopts two kinds and helps slag agent slag making, heating is worked as silicon liquid temp and is reached 1550 ℃ of left and right, add the first of fritting to help slag agent, continue to be warming up to 1650 ℃ of left and right, add the second of fritting to help slag agent, slag making complete purify after in polysilicon the content of B impurity below 1ppm.Conventionally selected slag agent will meet the following conditions conventionally: (1) avoids more impurity; (2) provide good mobility; (3) provide lower melt temperature, make slag keep molten state; (4) help the density of slag agent density and Pure Silicon Metal will have certain difference; (5) provide enough oxygenants fully to react with the B in silicon liquid.
Conventionally the slag system of studying mainly concentrates on CaO-SiO 2, Na 2o-SiO 2, appropriate interpolation CaF 2contribute to reduce the melt temperature of slag system, expand its basicity scope, in addition Al 2o 3as a kind of neutral oxide also frequent component as slag agent.Theoretically, reduce production costs, improve except boron efficiency, must improve its partition ratio, partition ratio is closely related with the component of slag agent, so the selection of slag agent is extremely important.
Summary of the invention
The object of the present invention is to provide a kind of method of removing boron from industrial silicon phosphorus impurities.
The present invention includes following steps:
1), by slag charge 2 fritting, described slag charge 2 is CaO-CaSi 2, by mass percentage, CaO is 40%~70%, CaSi 2be 30~50%;
2) slag charge 1 is pressed into slag ball, puts part slag charge 1 and industrial silicon into crucible, vacuumize, open medium frequency induction power supply heating, make material melting, described slag charge 1 is SiO 2-Na 2cO 3-CaF 2, by mass percentage, SiO 2be 40%~80%, Na 2cO 3be 20%~50%, CaF 2be 5%~20%;
3) power to the 80~100kW of rising medium frequency induction power supply, when temperature is during at 1300~1500 ℃, part slag charge 2 is joined in crucible to aeration-agitation, power to the 100~120kW of continuation rising medium frequency induction power supply, when temperature is during at 1600~1800 ℃, part slag charge 1 is joined in crucible, then aeration-agitation, power reduced to 80kW, maintain for some time, treat that temperature lowers;
4) repeating step 3);
5) after slag making, silicon liquid is poured into and accepted crucible, standing cooling rear taking-up silicon ingot, physics fragmentation obtains the polycrystal silicon ingot of purifying.
In step 1), the temperature of described fritting can be 1650~1850 ℃; By mass percentage, CaO can be 50%~60%, CaSi 2be 40~50%;
In step 2) in, described in be pressed into slag ball and can adopt spherical grinding tool, the diameter of described slag ball can be 5~20cm; By mass percentage, SiO 2can be 50%~70%; Na 2cO 3can be 30%~45%; CaF 2can be 8%~15%; Described part slag charge 1 can be 1 with the mass ratio of industrial silicon: (10~0.5), preferably 1: (5~0.5), are preferably 1: (2.5~0.5); Described part slag charge 1 can account for 1/3~1/2 of whole slag charges 1 in mass ratio; The described vacuum tightness vacuumizing can be below 450Pa.
In step 3), the gas of described aeration-agitation can be Ar gas, and the time of described aeration-agitation can maintain 1~10min, preferably maintains 2~5min; The gas of described aeration-agitation again can be Cl 2, the time of described aeration-agitation again can be 2~15min, is preferably 3~10min.
In step 4), the number of times of described repetition can be 3~10 times, is preferably 4~6 times.
In step 5), the time of described slag making can be 20~80min, is preferably 30~60min; The described standing time can be 40~60min.
Prepared polycrystal silicon ingot, adopts ICP-MS after sampling, i.e. plasma inductance coupling spectrometer analysis is measured the content that remains B and P in silicon.
Slag former partition ratio of the present invention is the highest can arrive 4, repeatedly the 2 kinds of different slag systems that add of repeatability are compared with traditional slag practice, can better arrive the effect except P except B, silicide in slag charge 2 components is as additive, it can be good at dissolving P, by P impurity with phosphatic form from silicon, be transferred to slag mutually in, need not adopt high vacuum to remove P and just phosphorus can be dropped to below the content that meets solar level standard.Adopt this novel slag agent, the content of B can be reduced to 0.4~1ppmw from 10ppmw, P content is reduced to 1~1.8ppmw from 30ppmw.Whole technological operation is simple, and cost is moderate, low for equipment requirements, is applicable to suitability for industrialized production.
Embodiment
Embodiment 1
1) slag silicon ratio selects 1: 1, gets slag charge 1:Na 2cO 3(30%wt)-SiO 2(60%wt)-CaF 2(10%wt) 25kg and slag charge 2:CaO(55%)-CaSi 2(45%) 25kg, places separately, and slag charge 2 is carried out to presmelting, and temperature is controlled at 1700~1850 ℃, and it is the bead of 5cm that slag charge 1 becomes diameter through art breading; The industrial silicon (B in industrial silicon, the content of P is respectively 10ppmw and 30ppmw) of getting 1/2 slag charge 1 and 50kg mixes and adds in crucible.
2) be evacuated to vacuum tightness below 500Pa, start medium frequency induction power supply heating, power increases gradually, and plumbago crucible starts induction heating, and silicon starts fusing;
3) as power to 80~100kW, when temperature is 1300~1500 ℃, a part of slag charge 2 is joined in crucible by storage hopper, venting pin drops to 3cm place in liquid, and logical Ar gas agitating stops after ventilation 5min;
4) continue rising power to 100~120kW, when temperature is 1600~1800 ℃, a part of slag charge 1 is added in crucible, start to the logical Cl of system 2, aeration-agitation, Ventilation Rate is 1L/min, the aeration-agitation time is 5min, then reduces power to 80kW, maintains for some time, treats that temperature lowers.
5) repeating step (3)~(4), multiplicity is 4 times;
6) after slag making, venting pin is lifted away to crucible, silicon liquid is transferred to accepts plumbago crucible, standing treat its naturally cooling after, broken silicon ingot, measures after melting B in silicon, the content of P by plasma inductance coupling mass spectrograph (ICP-MS) after sampling.The about 45min consuming time of whole slagging process, through ICP-MS, recording B content in silicon is 0.5ppmw, P content is 1ppmw.
Embodiment 2: technological process is with embodiment 1, slag agent components unchanged used, and slag charge 1 is still Na 2cO 3(30%wt)-SiO 2(60%wt)-CaF 2(10%wt), slag system 2 is CaO(55%)-CaSi 2(45%); Slag charge 50kg, slag charge 1 and slag charge 2 respectively account for half, industrial silicon 50kg, slag charge 1 becomes the bead sample of 10cm through art breading, and slag charge 2 carries out fritting, and prefusing temperature is controlled at 1800 ℃; 1/2 slag charge 1 is mixed and put in plumbago crucible with industrial silicon, vacuumize, start Frequency Induction Heating, slowly increase power, during power to 80~100kW, add a part of slag charge 2 logical Ar gas 3min, continue rising power to 100~120kW, add a part of slag charge 1, logical Cl 2after stirring 5min, stop and reducing power to 80kw, maintain for some time, after lowering, temperature again adds power, then repeat successively to add slag charge 2 and slag charge 1, repeat 5 times, after slag making 50min, smelting furnace liquid is transferred to and is accepted in plumbago crucible, standing after cooling silicon ingot, sampling detects to such an extent that B content is 0.65ppmw through ICP-MS, P content is 1ppmw.
Embodiment 3: technological process is with embodiment 1, and slag charge 1 used is adjusted into Na 2cO 3(40%wt)-SiO 2(50%wt)-CaF 2(10%wt), slag charge 2 is constant is still CaO(55%)-CaSi 2(45%); Slag charge 50kg, slag charge 1 and slag charge 2 respectively account for half, industrial silicon 50kg, slag charge 1 becomes the bead sample of 5cm through art breading, and slag charge 2 carries out fritting, and prefusing temperature is controlled at 1800 ℃; 1/2 slag charge 1 is mixed and put in plumbago crucible with industrial silicon, vacuumize, start Frequency Induction Heating, slowly increase power, during power to 80~100kW, add a part of slag charge 2 logical Ar gas 5min, continue rising power to 100~120kW, add a part of slag charge 1, logical Cl 2after stirring 5min, stop and reducing power to 80kW, maintain for some time, after lowering, temperature again adds power, then repeat successively to add slag charge 2 and slag charge 1, repeat 4 times, after slag making 50min, smelting furnace liquid is transferred to and is accepted in plumbago crucible, standing after cooling silicon ingot, sampling detects to such an extent that B content is 0.4ppmw through ICP-MS, P content is 1.5ppmw.
Embodiment 4: technological process is with embodiment 1, and slag charge 1 used is Na 2cO 3(30%wt)-SiO 2(60%wt)-CaF 2(10%wt), slag charge 2 is adjusted into CaO(60%)-CaSi 2(40%); Slag charge 50kg, slag charge 1 and slag charge 2 respectively account for half, industrial silicon 50kg, slag charge 1 becomes the bead sample of 5cm through art breading, and slag charge 2 carries out fritting, and prefusing temperature is controlled at 1750 ℃; 1/2 slag charge 1 is mixed and put in plumbago crucible with industrial silicon, vacuumize, start Frequency Induction Heating, slowly increase power, during power to 80~100kW, add a part of slag charge 2 logical Ar gas 5min, continue rising power to 100~120kW, add a part of slag ball 1, logical Cl 2after stirring 5min, stop and reducing power to 80kW, maintain for some time, after lowering, temperature again adds power, then repeat successively to add slag charge 2 and slag charge 1, repeat 4 times, after slag making 55min, smelting furnace liquid is transferred to and is accepted in plumbago crucible, standing after cooling silicon ingot, sampling detects to such an extent that B content is 0.5ppmw through ICP-MS, P content is 1.8ppmw.
Embodiment 5: technological process is with embodiment 1, and slag charge 1 used is adjusted into Na 2cO 3(30%wt)-SiO 2(60%wt)-CaF 2(10%wt), slag charge 2 is CaO(55%)-CaSi 2(45%).Slag charge 50kg, slag charge 1 and slag charge 2 respectively account for half, industrial silicon 50kg, slag charge 1 becomes the bead sample of 5cm through art breading, and slag charge 2 carries out fritting, and prefusing temperature is controlled at 1800 ℃; 1/2 slag charge 1 is mixed and put in plumbago crucible with industrial silicon, vacuumize, start Frequency Induction Heating, slowly increase power, during power to 80~100kW, add a part of slag charge 2 logical Ar gas 5min, continue rising power to 100~120kW, add a part of slag charge 1, logical Cl 2after stirring 5min, stop and reducing power to 80kW, maintain for some time, after lowering, temperature again adds power, then repeat successively to add slag charge 2 and slag charge 1, repeat 6 times, after slag making 60min, smelting furnace liquid is transferred to and is accepted in plumbago crucible, standing after cooling silicon ingot, sampling detects to such an extent that B content is 0.65ppmw through ICP-MS, P content is 1ppmw.
Embodiment 6: technological process is with embodiment 1, and slag charge 1 used is adjusted into Na 2cO 3(40%wt)-SiO 2(50%wt)-CaF 2(10%wt), slag charge 2 is constant is still CaO(55%)-CaSi 2(45%).Slag charge 50kg, slag charge 1 and slag charge 2 respectively account for half, industrial silicon 50kg, slag charge 1 becomes the bead sample of 8cm through art breading, and slag charge 2 carries out fritting, and prefusing temperature is controlled at 1750 ℃; 1/2 slag charge 1 is mixed with industrial silicon and put in the plumbago crucible of processing through coating, vacuumize, start Frequency Induction Heating, slowly increase power, during power to 80~100kW, add a part of slag charge 2 logical Ar gas 5min, continue rising power to 100~120kW, add a part of slag charge 1, logical Cl 2after stirring 5min, stop and reducing power to 80kW, maintain for some time, after lowering, temperature again adds power, then repeat successively to add slag charge 2 and slag charge 1, repeat 5 times, after slag making 50min, smelting furnace liquid is transferred to and is accepted in plumbago crucible, standing after cooling silicon ingot, sampling detects to such an extent that B content is 0.55ppmw through ICP-MS, P content is 1.5ppmw.

Claims (11)

1. remove a method for boron from industrial silicon phosphorus impurities, it is characterized in that comprising the following steps:
1), by slag charge 2 fritting, described slag charge 2 is CaO-CaSi 2, by mass percentage, CaO is 50%~60%, CaSi 2be 40~50%; The temperature of described fritting is 1650~1850 ℃;
2) slag charge 1 is pressed into slag ball, puts part slag charge 1 and industrial silicon into crucible, vacuumize, open medium frequency induction power supply heating, make material melting, described slag charge 1 is SiO 2-Na 2cO 3-CaF 2, by mass percentage, SiO 2be 50%~70%, Na 2cO 3be 30%~45%, CaF 2be 8%~15%; Described part slag charge 1 is 1 with the mass ratio of industrial silicon: (10~0.5); Described part slag charge 1 accounts for 1/3~1/2 of whole slag charges 1 in mass ratio; The described vacuum tightness vacuumizing is below 450Pa;
3) power to the 80~100kW of rising medium frequency induction power supply, when temperature is during at 1300~1500 ℃, part slag charge 2 is joined in crucible to aeration-agitation, power to the 100~120kW of continuation rising medium frequency induction power supply, when temperature is during at 1600~1800 ℃, part slag charge 1 is joined in crucible, then aeration-agitation, power reduced to 80kw, maintain for some time, treat that temperature lowers;
4) repeating step 3);
5) after slag making, silicon liquid is poured into and accepted crucible, standing cooling rear taking-up silicon ingot, physics fragmentation obtains the polycrystal silicon ingot of purifying.
2. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 2) in, described in be pressed into slag ball and adopt spherical grinding tool, the diameter of described slag ball is 5~20cm.
3. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 2) in, described part slag charge 1 is 1 with the mass ratio of industrial silicon: (2.5~0.5).
4. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 3), and the gas of described aeration-agitation is Ar, and the time of described aeration-agitation maintains 1~10min.
5. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 4, is characterized in that the time of described aeration-agitation maintains 2~5min.
6. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 3), and the gas of described aeration-agitation is again Cl 2, the time of described aeration-agitation is again 2~15min.
7. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 6, described in it is characterized in that, the time of aeration-agitation is 3~10min again.
8. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 4), and the number of times of described repetition is 3~10 times.
9. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 8, the number of times that it is characterized in that described repetition is 4~6 times.
10. a kind of method of removing boron from industrial silicon phosphorus impurities as claimed in claim 1, is characterized in that in step 5), and the time of described slag making is 20~80min; The described standing time is 40~60min.
11. a kind of methods of removing boron from industrial silicon phosphorus impurities as claimed in claim 10, the time that it is characterized in that described slag making is 30~60min.
CN201210078794.4A 2012-03-22 2012-03-22 Method for removing boron-phosphorus impurities from silicon metal Expired - Fee Related CN102616787B (en)

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CN104276572B (en) * 2013-07-02 2016-08-10 青岛隆盛晶硅科技有限公司 The slag former of polycrystalline silicon medium melting and using method thereof
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