CN101671023B - Boron-removing purification method of polysilicon - Google Patents

Boron-removing purification method of polysilicon Download PDF

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Publication number
CN101671023B
CN101671023B CN2009101125465A CN200910112546A CN101671023B CN 101671023 B CN101671023 B CN 101671023B CN 2009101125465 A CN2009101125465 A CN 2009101125465A CN 200910112546 A CN200910112546 A CN 200910112546A CN 101671023 B CN101671023 B CN 101671023B
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silicon
slag
boron
polysilicon
purification
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CN101671023A (en
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罗学涛
蔡靖
李锦堂
郑淞生
陈文辉
沈晓杰
龚惟扬
陈朝
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Xiamen University
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Abstract

The invention discloses a boron-removing purification method of polysilicon, relates to a boron-removing purification process of polysilicon, and provides a boron-removing purification method of polysilicon, which has high efficiency, low cost and simple operation and is applicable to large-scale industrial production. The boron-removing purification method comprises the following steps; selecting silicon metal as the raw material, putting the silicon metal into a graphite crucible, conducting vacuum-pumping, and starting a mid-frequency induction power for heating to melt the silicon metal in the graphite crucible; when all the silicon is melt, introducing inert gas into the system, increasing the power to lead the liquid silicon temperature to be kept between 1500 DEG C and 1600 DEG C, adding a first pre-melted slagging-promoting agent for reaction, further increasing the power to lead the liquid silicon temperature to be kept between 1600 DEG C and 1700 DEG C, and adding a second pre-melted slagging-promoting agent; after completing slagging, pouring the liquid silicon into a pouring crucible, standing, and taking out silicon ingots after cooling, thus obtaining the purified polysilicon ingots.

Description

A kind of boron-removing purification method of polysilicon
Technical field
What the present invention relates to a kind of polysilicon removes the boron purifying technique, especially relates to a kind of boron-removing purification method of polysilicon that adopts metallurgy method.
Background technology
For meeting preparation solar cell needs, the content of boron must be less than 0.3ppmw in the solar-grade polysilicon.Because physical properties is close, be difficult to effectively remove the boron impurity in the silicon.At present, main metallurgy method is removed boron technology and is comprised: air blowing slag making, alloy directionally solidified, plasma melting etc.
Wherein, plasma process is complicated, and cost is higher, alloy directionally solidifiedly how to realize that in suitability for industrialized production the effective of alloyed metal such as Si and Al separate, and still remains further research.Therefore, the air blowing slag making is the main method that present low-cost metallurgy method is removed boron.Air blowing can be implemented separately with slag making, also can carry out simultaneously.
People such as C.P.Khattak (C.P.Khattak.et al.A simple process to remove boron from metallurgicalgrade silicon.Solar Energy Materials﹠amp; Solar Cells, 2002, the reactant gases when 74:967-971) pointing out to blow mainly contains compositions such as O, H, Cl, generates volatile gases with the B reaction and discharges.
U.S. Pat 20070180949 (Kondo Jiro et al., Method for removing boron from silicon) discloses the method that a kind of air blowing removes B, is blown into by Ar, H from silicon liquid bottom 2, H 2O and O 2Deng the reactant gases of forming, B can reduce to 5ppmw from 25ppmw.
U.S. Pat 5788945 (Anders Schei, Method for refining of silicon) discloses a kind of by add the method that helps the slag agent continuously in silicon liquid, and helping slag agent composition is 60%CaO and 40%SiO 2, B drops to 1ppmw from 40ppmw.
U.S. Pat 20050139148 (Fujiwara Hiroyasu et al., Silicon purifying method, slag forpurifying silicon, and purified silicon) method that adopts air blowing and slag making to carry out simultaneously, reactant gases is that water vapour content is 30% Ar, be blown into by the turning unit central duct, help the slag agent to select SiO for use 2And CaO, B can reduce to 0.8ppmw from 7.4ppmw.
Still there is following problem in the air blowing slag practice in industrial application: at first, and the still difficult purity requirement that reaches solar-grade polysilicon of the removal effect of B.Secondly, there is limitation in the air blowing mode, and fragile, the corrosion of ventilation member is higher to equipment requirements.And under the high temperature, gas meeting of partial oxygen voltinism and pasc reaction cause the silicon loss.
For slag making, at first be the selection that helps the slag agent, need satisfy following primary condition: (1) can fully react with the B in the silicon liquid; (2) avoid introducing too much impurity; (3) have lower melt temperature, make in slagging process, to keep molten state; (4) help the density of slag agent density and Pure Silicon Metal that certain difference is arranged, the slag that makes generation floats over the liquid-state silicon surface or is sunken to the bottom when leaving standstill, so that the slag gold separates.
At present, what be used to purify helps the slag agent mainly based on the calcium-silicate system, because the partition ratio of B is generally very little, remove the B effect preferably if want to obtain, must strengthen and help slag agent consumption, fully react with oxygenant that capacity is provided and the B in the silicon liquid, even need melt back, and as above-mentioned U.S. Pat 5788945, melting 20kg silicon, what just will add 40kg helps the slag agent, and this does not obviously meet the requirement that low-cost industrialization is produced.Consider to help and also can contain certain B impurity in the slag agent that the slag making experiment of the big quantity of slag also can produce certain pollution to silicon.In addition, the unexposed patent of part adopts barium salt can effectively improve the partition ratio of B, but this slag system melt temperature is higher, simultaneously, owing to select the single slag agent that helps for use, scum silica frost no matter, or sediment (as barium salt), in the actual slagging process, the exposure level of slag system and silicon liquid is limited, causes reaction to be difficult to fully carry out.
Summary of the invention
The objective of the invention is to remove the existing limitation of method of B impurity in the polysilicon, provide a kind of efficient at existing metallurgy method, low cost, simple to operate, the boron-removing purification method of polysilicon of suitable large-scale industrial production.
Technical scheme of the present invention is to adopt compound slag making, successively add two kinds have a heterogeneity help the slag agent, oxidizing reaction takes place with B in the silicon liquid, generate boron oxide compound, enter in the slag system, separate by the slag gold, can effectively remove B impurity.Method is by the induction heating plumbago crucible, in rough vacuum, under the inert atmosphere, that selects two kinds of heterogeneities helps the slag agent, after the fritting, successively join in the silicon liquid with the timed interval by a certain percentage, control differential responses temperature and time utilizes induction stirring, and the B in slag and the silicon liquid is fully reacted, form polynary slag phase, realize that by leaving standstill the slag gold separates.
The present invention includes following steps:
1) selecting Pure Silicon Metal for use is raw material;
2) feed metal silicon is put into plumbago crucible, vacuumize, start the medium frequency induction power supply heating, make the Pure Silicon Metal fusing in the plumbago crucible;
3) after silicon all melts, in system, feed rare gas element, improve power, make the silicon liquid temp remain on 1500～1600 ℃, first kind that adds fritting is helped slag agent reaction, further improve power, make the silicon liquid temp remain on 1600～1700 ℃, second kind that adds after the fritting is helped the slag agent again;
4) treat that slag making is finished after, pour silicon liquid into cast with in the crucible, leave standstill, silicon ingot, the polycrystal silicon ingot after obtaining purifying are taken out in the cooling back.
In step 1), described Pure Silicon Metal can be bulk or powdery, and the purity of Pure Silicon Metal is preferably 99% (2N), and wherein B content is 15ppmw.
In step 2) in, described vacuumizing starts the medium frequency induction power supply heating, preferably reaches 500Pa when following when vacuum tightness, and the startup medium frequency induction power supply heats, and the power of medium frequency induction power supply preferably is controlled at 40～120kw.
In step 3), described first kind to help the slag agent be Na 2CO 3-SiO 2, wherein, by mass percentage, SiO 2Content be 50%～60%; Described second kind is helped the slag agent to be selected from SiO 2With oxide compound, oxyhydroxide, fluorochemical and the carbonate of alkaline-earth metal such as Ca, Mg, Ba, wherein, by mass percentage, SiO 2Content be no more than 30%; Described rare gas element is Ar etc.; First kind of described adding fritting is helped the time of slag agent reaction to be preferably 15～45min, and second kind after the adding fritting is helped the time of slag agent to be preferably 30～60min.
In step 4), described silicon liquid is poured into poured into a mould with in the crucible, and the time of leaving standstill is preferably 40～60min.
Can measure the boron impurity content of melting front and back.
Adopt method of purification of the present invention, can make the highest 0.18ppmw of being reduced to of content of B, meet the purity requirement of solar-grade polysilicon.
It is generally acknowledged that B exists with atomic form, add and help the slag agent that make B form oxide compound, its thermodynamic stability in slag will be easy to be absorbed mutually by slag far above in the silicon.But because the physical properties of B and silicon is close, oxidisability is suitable, and when adopting slag practice to remove B, B is difficult to oxidized, can't enter the slag phase, and promptly the partition ratio of B (B is at content/B the content in silicon liquid of slag in mutually) is very low.So, for general slagging process, remove the B effect preferably if will obtain, must strengthen the consumption that helps the slag agent, and therefore the present invention obtains and well removes the B effect owing to adopted rational two kinds to help the slag agent.
Because the oxide compound free energy of formation temperature relation of each constituent element is known from silicon, under identical oxygen pressure and temperature, Na is relative with the avidity between the O minimum, by the selective oxidation principle, with CaO, SiO 2Compare Na 2O is easier with B following oxidizing reaction to take place:
[B]+3/2(Na 2O)＝3[Na]+(BO 1.5)
Therefore, in slagging process, can introduce the Na of strong oxidizing property earlier 2O, promote the oxidation of B, according to K.Suzuki and N.Sano at paper " Thermodynamics of boron in a silicon melt " (Metallurgical and Materials Transactions B, Volume 25B, 1994) research in, the BO of generation 1.5Activity is low in basic slag system, more tends towards stability this and BO 1.5It itself is the character unanimity of acidic oxide.
After treating that above-mentioned oxidizing reaction finishes, add new alkaline auxiliary slag agent again, make BO 1.5Enter the slag phase rapidly, and further with silicon liquid in remaining B oxidizing reaction takes place, thereby significantly improve the partition ratio of B.
Therefore, help the slag agent, select Na for use for first first kind of adding 2CO 3, in silicon liquid, resolve into Na 2O and CO 2, the latter can play the effect that promotes stirring.Consider under the hot conditions fusion Na 2The volatilization of O and corrosive nature are removed Na 2CO 3Be equipped with a certain proportion of SiO outward, 2, according to Na 2O-SiO 2System's phasor is for preventing to form the quartzy phase of infusible, SiO 2Content is 50%～60%, in this composition range, more than 1100 ℃, just can form uniform liquid phase region, thereby make slag system can keep the liquid phase state of long period, helps the removal of B.
Help the slag agent to select CaO-MgO-SiO for use 2, CaO-BaO-SiO 2Can effectively improve the partition ratio of B, and the partition ratio of B is with slag system alkalescence (CaO/SiO 2) enhancing and increase.
In addition, add a spot of CaF 2Deng alkaline-earth metal fluoride, except that can reducing system fusing point and viscosity, the basicity of slag phase is increased, this is because following reaction:
Si 2O 7 6-+2F -＝2[SiO 3F] 3-+O 2-
Wherein, the F of introducing -Make silicate network structure generation scission of link, bridging oxygen becomes free oxygen.But CaF 2Too much etc. add-on, to the plumbago crucible serious corrosion.
Therefore, help the slag agent for back second kind of adding, mainly by SiO 2Form with oxide compound, oxyhydroxide, carbonate and the fluorochemical of alkaline-earth metal such as Ca, Mg, Ba, wherein, SiO 2Content is no more than 30%, is alkalescence to guarantee slag system, promotes the boron oxide compound (BO that forms after the first step slag making 1.5) absorption.
In sum, compare with the B method of removing of existing metallurgy method solar-grade polysilicon, the present invention is innovated on the basis of traditional slagging process, adopt compound slag making, that selects two kinds of heterogeneities for use helps the slag agent, first kind of oxidation that helps the slag agent effectively to promote B, the boron oxide compound of generation can be helped the basic slag of slag agent to absorb mutually by second kind rapidly.Simultaneously, second kind is helped the slag agent also can oxidizing reaction further take place with remaining B in the silicon liquid, significantly improves the partition ratio of B, has the good effect of boron that removes, and helps slag agent consumption thereby reduced effectively, need not the repetition slag making, this is not seen so far relevant report.Above method is simple to operate, and cost is low, and device is transformed by traditional intermediate frequency furnace, is convenient to extensive Industry Promotion, has extremely considerable market outlook.
Embodiment
Below provide some embodiment of boron-removing purification method of polysilicon of the present invention.
Embodiment 1
1) takes by weighing the feed metal silicon 50kg that B concentration is about 15ppmw.
2) press mass ratio and mix Na at 50: 50 2CO 3With SiO 2Powder helps the slag agent as first, 1400 ℃ of following fritting, and this mass ratio that helps slag agent and raw silicon is 1: 10 (slag-metal rate is 0.1), i.e. 5kg.
3) press mass ratio 60: 15: 25 mixed C aO, CaF 2, SiO 2Powder helps the slag agent as second, 1500 ℃ of following fritting, and this mass ratio that helps slag agent and raw silicon is 1.5: 10 (slag-metal rate is 0.15), i.e. 7.5kg.
4) feed metal silicon is put into plumbago crucible, vacuumize, when vacuum tightness reaches 500Pa when following, start Frequency Induction Heating, power is at 50kw, and the Pure Silicon Metal in plumbago crucible melts fully.
5) feed a certain amount of Ar, improve power, make the silicon liquid temp reach 1500 ℃ to 60kw, add first of fritting and help the slag agent, behind the slag making 15min, further improve power to 80kw, make the silicon liquid temp remain on 1600 ℃, second after the adding fritting helps the slag agent, slag making 30min.
6) treat that slag making is finished after, pour silicon liquid into cast with in the crucible, leave standstill 40min under 1450 ℃, silicon ingot is taken out in the cooling back, each is about 1/10 to remove end to end part, and the polycrystal silicon ingot after obtaining purifying records by sims (SIMS) that B content is 0.56ppmw in the polycrystal silicon ingot.
Embodiment 2
Technological process is with embodiment 1.First to help the mass ratio of slag agent and raw silicon be 3: 10 (slag-metal rate is 0.3), i.e. 15kg.Press 60: 10: 30 mixed C a (OH) of mass ratio 2, CaF 2, SiO 2Powder helps the slag agent as second, with the mass ratio of raw silicon be 2: 10 (slag-metal rate is 0.2), i.e. 10kg.After treating that silicon all melts, improve power, make the silicon liquid temp reach 1550 ℃ to 70kw, add first of fritting and help the slag agent, slag making 45min further improves power to 90kw, make the silicon liquid temp remain on 1650 ℃, second after the adding fritting helps the slag agent, slag making 60min.After treating that slag making is finished, pour silicon liquid into cast with in the crucible, leave standstill 60min under 1450 ℃, silicon ingot is taken out in the cooling back, each is about 1/10 to remove end to end part, and the polycrystal silicon ingot after obtaining purifying records by sims (SIMS) that B content is 0.29ppmw in the polycrystal silicon ingot.
Embodiment 3
Technological process is with embodiment 1.First to help the mass ratio of slag agent and raw silicon be 1.5: 10 (slag-metal rate is 0.15), i.e. 7.5kg.Press mass ratio and mix BaCO at 55: 15: 30 3, CaF 2, SiO 2Powder helps the slag agent as second, 1700 ℃ of following fritting.After treating that silicon all melts, improve power, make the silicon liquid temp reach 1550 ℃ to 70kw, add first of fritting and help the slag agent, behind the slag making 25min, further improve power to 100kw, make the silicon liquid temp remain on 1700 ℃, second after the adding fritting helps the slag agent, slag making 60min.After treating that slag making is finished, pour silicon liquid into cast with in the crucible, leave standstill 60min under 1450 ℃, silicon ingot is taken out in the cooling back, each is about 1/10 to remove end to end part, and the polycrystal silicon ingot after obtaining purifying records by sims (SIMS) that B content is 0.18ppmw in the polycrystal silicon ingot.
Embodiment 4
Technological process is with embodiment 1.Press mass ratio and mix Na at 40: 60 2CO 3With SiO 2Powder helps the slag agent as first, 1300 ℃ of following fritting.Pressed mass ratio 50: 10: 15: 25 mixed C aCO 3, CaF 2, Ba (OH) 2, SiO 2Powder helps the slag agent as second, 1700 ℃ of following fritting.After treating that silicon all melts, improve power, make the silicon liquid temp reach 1600 ℃ to 80kw, add first of fritting and help the slag agent, behind the slag making 25min, further improve power to 100kw, make the silicon liquid temp remain on 1700 ℃, second after the adding fritting helps the slag agent, slag making 45min.After treating that slag making is finished, pour silicon liquid into cast with in the crucible, leave standstill 60min under 1450 ℃, silicon ingot is taken out in the cooling back, each is about 1/10 to remove end to end part, and the polycrystal silicon ingot after obtaining purifying records by sims (SIMS) that B content is 0.43ppmw in the polycrystal silicon ingot.
Embodiment 5
Technological process is with embodiment 1.Metallic silicon raw material 100kg presses mass ratio and mixes Na at 44: 56 2CO 3With SiO 2Powder helps the slag agent as first, with the mass ratio of raw silicon be 2: 10 (slag-metal rate is 0.2), i.e. 20kg.1320 ℃ of following fritting.Press 65: 7: 28 mixed C aCO of mass ratio 3, CaF 2, SiO 2Powder helps the slag agent as second, with the mass ratio of raw silicon be 3: 10 (slag-metal rate is 0.3), i.e. 30kg, 1600 ℃ of following fritting.After treating that silicon all melts, improve power, make the silicon liquid temp reach 1550 ℃ to 70kw, add first of fritting and help the slag agent, behind the slag making 25min, further improve power to 100kw, make the silicon liquid temp remain on 1700 ℃, second after the adding fritting helps the slag agent, slag making 30min.After treating that slag making is finished, pour silicon liquid into cast with in the crucible, leave standstill 40min under 1450 ℃, silicon ingot is taken out in the cooling back, each is about 1/10 to remove end to end part, and the polycrystal silicon ingot after obtaining purifying records by sims (SIMS) that B content is 0.26ppmw in the polycrystal silicon ingot.
Comparative Examples 1
Help the slag agent except not adding second, with first help the mass ratio of slag agent and raw silicon to increase to 5: 10 (slag-metal rate is 0.5), the i.e. 25kg.Carry out the 60min slag making under the condition similar to embodiment 3, the B content of measuring after the melting is 1.11ppmw.
Comparative Examples 2
Help the slag agent except not adding first, with second help the mass ratio of slag agent and raw silicon to increase to 5: 10 (slag-metal rate is 0.5), the i.e. 25kg.Carry out the 60min slag making under the condition similar to embodiment 3, the B content of measuring after the melting is 2.07ppmw.

Claims (7)

1. boron-removing purification method of polysilicon is characterized in that may further comprise the steps:
1) selecting Pure Silicon Metal for use is raw material;
2) feed metal silicon is put into plumbago crucible, vacuumize, start the medium frequency induction power supply heating, make the Pure Silicon Metal fusing in the plumbago crucible;
3) after silicon all melts, in system, feed rare gas element, improve power, make the silicon liquid temp remain on 1500～1600 ℃, first kind that adds fritting is helped slag agent reaction, further improves power, makes the silicon liquid temp remain on 1600～1700 ℃, second kind that adds after the fritting is helped the slag agent again, and described first kind to help the slag agent be Na 2CO 3-SiO 2, wherein, by mass percentage, SiO 2Content be 50%～60%; Second kind is helped the slag agent, by SiO 2Form with oxide compound, oxyhydroxide, carbonate and the fluorochemical of Ca, Mg, Ba, wherein, by mass percentage, SiO 2Content is no more than 30%, and content of fluoride is 5%～15%;
4) treat that slag making is finished after, pour silicon liquid into cast with in the crucible, leave standstill, silicon ingot, the polycrystal silicon ingot after obtaining purifying are taken out in the cooling back.
2. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 1), and described Pure Silicon Metal is reguline metal silicon or granulated metal silicon, and the purity of Pure Silicon Metal is 99%.
3. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 2) in, described vacuumizing, start the medium frequency induction power supply heating, be to reach 500Pa when following when vacuum tightness, start the medium frequency induction power supply heating, the power of medium frequency induction power supply is controlled at 40～120kw.
4. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 3), and described rare gas element is Ar.
5. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 3), and first kind of time of helping the slag agent to react of described adding fritting is 15～45min.
6. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 3), and adding after the fritting second kind, to help the time of slag agent be 30～60min.
7. a kind of boron-removing purification method of polysilicon as claimed in claim 1 is characterized in that in step 4), and described silicon liquid is poured into poured into a mould with in the crucible, and the time of leaving standstill is 40～60min.
CN2009101125465A 2009-09-15 2009-09-15 Boron-removing purification method of polysilicon Expired - Fee Related CN101671023B (en)

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CN101837980B (en) * 2010-05-20 2011-12-14 厦门大学 Method for removing boron and phosphorus impurities in industrial silicon through sulphide
CN102344142B (en) * 2010-07-26 2013-11-06 比亚迪股份有限公司 Method for purifying silicon through removing boron
CN101948112B (en) * 2010-09-16 2012-09-12 北京应天阳光太阳能技术有限公司 Method for separating silicon from residuals
CN102602934B (en) * 2011-01-21 2013-09-18 北京应天阳光太阳能技术有限公司 Production method for removing slag agent of boron impurity in slagging method
CN102134076B (en) * 2011-01-25 2012-09-05 云南乾元光能产业有限公司 Method for removing boron impurity in metallurgical silicon
CN102320610B (en) * 2011-09-13 2013-02-27 山西纳克太阳能科技有限公司 Method for purifying solar-grade polysilicon to remove boron
CN102530954B (en) * 2012-03-07 2015-05-20 昆明理工大学 Composite refining agent for secondary refining to purify industrial silicon and remove boron
CN103570023B (en) * 2012-07-23 2017-02-08 东莞东阳光科研发有限公司 Slag-making and boron-removing method for industrial silicon
CN103011169B (en) * 2012-12-14 2014-05-07 厦门大学 Preparation method for sheet silicon
CN103833036B (en) * 2014-01-08 2016-05-11 福建兴朝阳硅材料股份有限公司 A kind of method of low cost corundum crucible slagging boron removal

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