CN102267699B - Silicon metal purification method based on oxide high-temperature solid-phase reaction - Google Patents
Silicon metal purification method based on oxide high-temperature solid-phase reaction Download PDFInfo
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- CN102267699B CN102267699B CN201110163381.1A CN201110163381A CN102267699B CN 102267699 B CN102267699 B CN 102267699B CN 201110163381 A CN201110163381 A CN 201110163381A CN 102267699 B CN102267699 B CN 102267699B
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Abstract
The invention provides a silicon metal purification method based on an oxide high-temperature solid-phase reaction. On the basis of the traditional silicon metal purification technology by using a slagging method, the method disclosed by the invention is mainly characterized in that: Al2O3 and SiO2 or MgO can undergo solid-phase reaction at high temperature to respectively generate mullite or spinel; meanwhile, the reaction speed can be controlled by selecting a crystal structure and micro morphology of raw materials or adding other oxides; and the controllable high-temperature solid-phase reaction can be realized. In the solid-phase reaction process, various component atoms of a reaction product are rearranged to form new crystal lattice. Because B has minimum atomic radius, the B impurity in the molten liquid silicon enters the gap position of the crystal lattice very easily, therefore, the method has a particular effect for eliminating the B impurity in silicon metal; meanwhile, the method has a better effect for eliminating other impurities. The method disclosed by the invention has the characteristics of low cost and simpleness of operation.
Description
Technical field
This patent belongs to semiconductor material preparing technical field, especially for " metallurgy method " purification techniques field of preparing the solar-grade polysilicon of solar cell.
Background technology
Along with global energy dilemma, environmental degradation and the restriction of United Nations to various countries' greenhouse gas emissions in recent years, Renewable Energy Development technology has become fundamental policy that realize Global Sustainable Development.Solar-photovoltaic technology is one of chief component in renewable energy technologies, and global photovoltaic industry obtains develop rapidly in recent years.
Current most solar cell is crystal silicon solar energy battery, and crystal silicon solar energy battery comprises monocrystaline silicon solar cell and polysilicon solar cell.For the preparation of the monocrystalline silicon piece of solar cell and polysilicon chip, all take sun level polysilicon (silicone content higher than 99.9999% or 6N level) or more highly purified high purity polycrystalline silicon is raw material, and these polysilicons for the higher degree of solar cell are also usually commonly referred to as polysilicon (Polysilicon).The preparation technology of monocrystalline silicon piece is first by crystal pulling method (Czochralski technology) growing single-crystal silicon rod, and silicon single crystal rod makes monocrystalline silicon piece after cutting.First the preparation technology of polysilicon chip casts polycrystal silicon ingot by directional solidification method (Directional solidification technology), and polycrystal silicon ingot makes polysilicon chip after cutting.These monocrystalline silicon pieces and polysilicon chip can be used to prepare solar cell after cleaning.
Due to the great demand of photovoltaic industry to polysilicon, the price of global polysilicon is always high, and source of goods is also more nervous.The Pure Silicon Metal that purity is lower (purity is 98%～99.5% left and right) is the starting material of preparing polysilicon, and Pure Silicon Metal can obtain polysilicon after suitable technique is purified.
Current, two technological lines of industrial main employing carry out purifying metal silicon, finally obtain polysilicon.Article one, technological line is the chemical route based on " Siemens Method ", and another is based on metallurgical technology " metallurgy method " route.Present stage, overwhelming majority production of polysilicon enterprise adopts " improved Siemens " of " Siemens Method " or its improvement version and " fluidized bed process " that variation is come, this method is more ripe, but in production process, energy consumption is large, the cost of prepared polysilicon is relatively high, thisly expensively in fact can restrict the competitive power of photovoltaic power generation technology in cost of electricity-generating, thereby may limit the large-scale application prospect of photovoltaic power generation technology.Technological line based on " metallurgy method " have power consumption less, advantage that product cost is low, " metallurgy method " technological line obtains the very big concern of photovoltaic industry circle in recent years, in the industry development route of low-cost photovoltaic generation technology in future, has important prospect.
Pure Silicon Metal contains plurality of impurities, comprise that metallic impurity are as Fe, Cu, Ti, Cr, Al, Mn etc., and nonmetallic impurity is as B, P, C, O etc.B and P are the main doped elements of crystal silicon semiconductor, and wherein the doping of B becomes p-type semi-conductor by silicon, and the doping of P becomes N-shaped semi-conductor by silicon.At present, the industrial crystal silicon chip for solar cell is p-type semi-conductor, be the crystalline silicon of mixing B, at P content extremely low and ignore under, the doping of B is generally higher than 0.2ppmw (1ppmw is not 1 millionth mass ratio), and the resistivity of crystalline silicon is approximately controlled in the scope of 0.5cm～3cm.Therefore, should be significantly lower than 0.2ppmw for the polycrystalline silicon raw material B content of solar cell.Certainly, because adulterating, P doping and B in crystalline silicon there is compensation effect, in actual production, crystalline silicon usually contains or has a mind to mix a small amount of P impurity (lower than B content) and compensates, in polysilicon, B can suitably relax containing quantitative limitation like this, such as B content can be in 0.6ppmw left and right.The polysilicon that in fact this P and the B compensation effect in crystalline silicon makes " metallurgy method " to purify can be applied to solar cell completely, finally makes the cost of crystal silicon solar energy battery further reduce.
In " metallurgy method " purifying technique of Pure Silicon Metal, Pure Silicon Metal is first through being ground into less particulate state, then adopt the method for pickling to remove most metallic impurity and a part of nonmetallic impurity, the purity of Pure Silicon Metal can reach 99.99% (that is 4N level).Wanting further to make the purity of Pure Silicon Metal to reach to prepare the requirement of solar cell is 6N level polysilicon, needs to adopt " slag practice ", " method for vacuum smelting ", " directional solidification method " etc. to carry out further purifying metal silicon." method for vacuum smelting " has good refining effect to the P impurity in Pure Silicon Metal, and this is because P has higher saturation vapour pressure, volatile; " directional solidification method " has good refining effect to the metallic impurity in Pure Silicon Metal, this is because the segregation coefficient of metallic impurity is very little, in directional freeze process, metallic impurity are ostracised out from the crystalline silicon of growing, and concentrate on silicon ingot top, as long as by being rich in the silicon ingot top excision of metallic impurity, obtain the crystalline silicon that metals content impurity is very low." method for vacuum smelting " and " directional solidification method " can make the P content in Pure Silicon Metal reach in 0.2ppmw, and metals content impurity is significantly lower than 0.1ppmw.
Can find out, " method for vacuum smelting " and " directional solidification method " has very desirable impurity elimination effect to the P impurity in Pure Silicon Metal and metallic impurity, can meet the requirement of preparing solar cell.Yet these two kinds of methods but do not have positive effect to the B impurity of removing in Pure Silicon Metal, this be because: the boiling point of (1) B is very high, and vapour pressure is little, and not volatile in " method for vacuum smelting ", removal effect is low; (2) segregation coefficient of B is very large, be maximum in all impurity elements, thereby " directional solidification method " does not almost have effect to the B impurity of removing in Pure Silicon Metal." slag practice " is an important step in Pure Silicon Metal " metallurgy method " purifying technique, " slag practice " all has good impurity-eliminating effect to the many impurity in Pure Silicon Metal, the removal of B impurity is also had to obvious effect, conventionally the B content in Pure Silicon Metal can be down to 2～3ppmw left and right.Slag former is selected conventionally as metal oxide or halogenide such as CaCO3, MgO, BaO, Al2O3, CaO, SiO2, CaF2, CaCl2, and the addition of slag former is generally 5%～40% left and right of Pure Silicon Metal weight.Slag former absorbs the various impurity in Pure Silicon Metal in molten state silicon, and slag former remains solid-state in molten state silicon (liquid-state silicon), or swims in the surface of liquid-state silicon or be deposited to the bottom of liquid-state silicon; In temperature-fall period, liquid-state silicon is solidified, and removes the slag former of absorption impurity, thereby reaches the object of purifying metal silicon.If want to make the B content in Pure Silicon Metal to be further down in 1ppmw, adopt traditional " slag practice " still to have very large technical difficulty, and its cost for purification also can be very high.
Summary of the invention
This patent is on the basis of existing " slag practice ", by selecting two or more oxide compound composite fluxing medium, there is high temperature solid state reaction in some oxide compound in these oxide compound composite fluxing mediums (temperature of fusion of silicon is about 1420 ℃) in molten state silicon, because the crystalline structure of this reaction product in high temperature solid state reaction process and microtexture are (as its grain surface/interface, dislocation, room etc.) change, simultaneously the complete or microtexture of slag former that has neither part nor lot in reaction of other unreacted is because significantly adjustment also will occur for the appearance of above-mentioned high temperature solid state reaction, these slag formers that comprise reaction product can absorb B and other various impurity effectively from molten state silicon, these impurity are absorbed by these slag formers, reach the object of the various impurity such as B in remarkable removal Pure Silicon Metal.Compared to traditional " slag practice ", this patent " slag practice " increases significantly to the refining effect of B impurity in Pure Silicon Metal, and the refining effect of other impurity of Pure Silicon Metal is also had greatly improved, and the overall cost for purification of Pure Silicon Metal is significantly reduced.
The technical solution adopted for the present invention to solve the technical problems is:
A kind of silicon metal purification method based on oxide high-temperature solid state reaction of this patent, comprises following processing step:
(1) weigh the γ-Al of certain mass
2o
3with BaO powder raw material, the quality of BaO accounts for γ-Al
2o
310～40% of quality, mixes thoroughly, ball milling 6～15 hours in ball mill then, and the object one of ball milling is by γ-Al
2o
3reduce with the particle size of BaO, the 2nd, further make γ-Al
2o
3mix with BaO, after ball milling completes, γ-Al
2o
3particle is surrounded by one deck BaO, and this will control γ-Al effectively
2o
3in the back in liquid-state silicon with SiO
2between solid state reaction.
(2) by γ-Al in solid state reaction (1)
2o
3with SiO
2between the mol ratio of 3: 2, according to the γ-Al taking in step (1)
2o
3molar weight, takes appropriate SiO
2powder raw material, then by weighed SiO
2raw material is positioned in ball mill ball milling 6～10 hours.
(3) resulting raw material in step (1) and step (2) is positioned over together in mixer and is mixed 0.5～1.5 hour, because mixer does not have the effect of refinement to feed particles, so the size of feed particles can not change in this step.Because of γ-Al
2o
3particle is surrounded by one deck BaO, so BaO is at γ-Al
2o
3with SiO
2between powder, form the barrier of a solid phase diffusion, thereby can effectively control the process of solid state reaction (1).
(4) the resulting compound of step (3) is made to spherical particle body that diameter is 3mm～10mm or the granule of other shapes by tablets press; these are slag former particle; then sintering 2～4 hours at 900 ℃～1050 ℃ temperature; after sintering, these slag former particles just have suitable mechanical strength; in use can be not broken; the slag former granule interior simultaneously forming so also contains more micropore, can improve its gettering effect.
(5) the resulting slag former particle of step (4) is joined in the liquid-state silicon of melting, the ratio that slag former accounts for siliceous amount is 20%～40%.The temperature of liquid-state silicon is about 1435 ℃, the γ-Al in slag former particle
2o
3with SiO
2start by solid state reaction (1) the generation mullite that reacts, the reaction deadline is relevant with Ball-milling Time with the middle BaO add-on of step (1), is generally 2～6 hours.In this step, constantly bottom blowing or top blast rare gas element stir liquid-state silicon, and slag former particle is fully contacted with liquid-state silicon, improve gettering efficiency.
(6) after step (5) slag making completes, by liquid-state silicon cooled and solidified, excision slag former, the silicon after being purified.
In above-mentioned steps mentioned slag former or slagging process, can add the slag former of other kind completely, so just can reach the refining effect of combined type, purification efficiency is higher.
This patent method adopts the technological line purifying metal silicon of oxide high-temperature solid state reaction, B impurity is wherein had to particularly preferred impurity elimination effect, after purification, the B impurity in Pure Silicon Metal can reach below 0.5ppmw, can reach the requirement of preparing polysilicon solar cell.It is pointed out that this patent method also has good impurity elimination effect to the impurity of other kind in Pure Silicon Metal.
Embodiment
Specific embodiment is further described a kind of silicon metal purification method based on oxide high-temperature solid state reaction of the present invention.
Embodiment 1
(1) divide another name γ-Al
2o
3powder 20kg (γ-Al
2o
3molecular weight be that 102,20kg is 196 moles), BaO powder 7kg, with mixer, mix thoroughly, then ball milling 8 hours in ball mill.
(2) by γ-Al in solid state reaction (1)
2o
3with SiO
2between the mol ratio of 3: 2, need SiO
2approximately 131 moles, amounting to into quality is 7.9kg.Take 12kg SiO
2powder raw material, is positioned in ball mill ball milling 6 hours.Here use excessive SiO
2the object of raw material is the SiO that makes unreacted complete
2still can bring into play itself existing slag former effect, useful to the impurity of other kind in removal Pure Silicon Metal.
(3) resulting raw material in above-mentioned steps (1) and step (2) is positioned over together in mixer and is mixed 1 hour.
(4) the resulting compound of step (3) being made to the spherical particle body that diameter is about 5mm by tablets press becomes slag former particle, then sintering 3 hours at 1000 ℃ of temperature.
(5) take the Pure Silicon Metal (B foreign matter content is 4.6ppmw) of 80kg pickling, be placed in crucible and be heated to melting liquefy silicon with induction furnace, the temperature of liquid-state silicon is about 1435 ℃.
(6) the resulting slag former particle of step (4) 23kg is joined in the liquid-state silicon of step (5), also add the CaCl of 2kg simultaneously
2as auxiliary slag former, both play the refining effect of combined type; Bottom blowing or top blast stirring of inert gas liquid-state silicon, make slag former fully contact with liquid-state silicon, improves purification efficiency.
(7) after the slag making removal of impurities of 4 hours, removing suspends melts the scum silica frost of silicon liquid level, to melt silicon and carefully slowly be poured in ingot mould (noting: sediment should not incline to), cooling, broken, grinding, the clean remaining slag former of pickling, obtain having the silicon of higher degree.
In order to test the speed of response of the solid state reaction (1) in slag former particle, in step (7), select different slag making except miscellaneous time, as 1,2,3,4 hour etc., find approximately to have for 1 hour 32% Al
2o
3participate in reaction, within 2 hours, approximately had 58% Al
2o
3participate in reaction, after 3 hours, approximately had 83% Al
2o
3participated in reaction, Al after 4 hours
2o
3all participated in reaction.Can see, in this slag making removal of impurities process of 4 hours, solid state reaction (1) is being carried out always.
After the slag making removal of impurities of above-mentioned steps (1)～(7), the B foreign matter content in Pure Silicon Metal has declined more than 10 times, reaches 0.41ppmw, other impurity 5 times of left and right that also declined.
Embodiment 2
1) divide another name γ-Al
2o
3powder 20kg (γ-Al
2o
3molecular weight be that 102,20kg is 196 moles), BaO powder 6kg, with mixer, mix thoroughly, then ball milling 10 hours in ball mill.
(2) by γ-Al in solid state reaction (2)
2o
3and the mol ratio of 1: 1 between MgO, needing MgO is 196 moles, amounting to into quality is 7.8kg.Take 13kg MgO powder raw material, be positioned in ball mill ball milling 6 hours.Here the object of using excessive MgO raw material is to allow the complete MgO of unreacted still can bring into play itself existing slag former effect, useful to the impurity of other kind in removal Pure Silicon Metal.
(3) resulting raw material in above-mentioned steps (1) and step (2) is positioned over together in mixer and is mixed 0.6 hour.
(4) the resulting compound of step (3) being made to the spherical particle body that diameter is about 8mm by tablets press becomes slag former particle, then sintering 2.5 hours at 1030 ℃ of temperature.
(5) take the Pure Silicon Metal (B foreign matter content is 5.5ppmw) of 80kg pickling, be placed in crucible and be heated to melting liquefy silicon with induction furnace, the temperature of liquid-state silicon is about 1435 ℃.
(6) the resulting slag former particle of step (4) 25kg is joined in the liquid-state silicon of step (5), also add the CaCO of 4.5kg simultaneously
3as auxiliary slag former, both play the refining effect of combined type; Bottom blowing or top blast stirring of inert gas liquid-state silicon, make slag former fully contact with liquid-state silicon, improves purification efficiency.
(7) after the slag making removal of impurities of 3 hours, removing suspends melts the scum silica frost of silicon liquid level, to melt silicon and carefully slowly be poured in ingot mould (noting: sediment should not incline to), cooling, broken, grinding, the clean remaining slag former of pickling, obtain having the silicon of higher degree.
In order to test the speed of response of the solid state reaction (2) in slag former particle, in step (7), select different slag making except miscellaneous time, as 1,2,3 hour etc., find approximately to have for 1 hour 38% Al
2o
3participate in reaction, within 2 hours, approximately had 75% Al
2o
3participated in reaction, Al after 3 hours
2o
3all participated in reaction.Can see, in this slag making removal of impurities process of 3 hours, solid state reaction (2) is being carried out always.
After the slag making removal of impurities of above-mentioned steps (1)～(7), the B foreign matter content in Pure Silicon Metal has declined 11 times, reaches 0.5ppmw, other impurity 5 times of left and right that also declined.
Above embodiment is only illustrative rather than definitive thereof technical scheme of the present invention, enforcement personnel can revise or some replacement accordingly to the present invention, and not departing from spirit of the present invention, any modification or local replacement, all should be encompassed in the middle of claim scope of the present invention.
Claims (1)
1. the silicon metal purification method based on oxide high-temperature solid state reaction, is characterized in that: comprise the steps:
(1) get the γ-Al of certain mass
2o
3with BaO powder raw material, the quality of BaO accounts for γ-Al
2o
310～40% of quality;
(2) mix thoroughly, in ball mill, ball milling is 6～15 hours, and the object one of ball milling is by γ-Al
2o
3reduce with the particle size of BaO, the 2nd, further make γ-Al
2o
3mix with BaO, after ball milling completes, γ-Al
2o
3particle is surrounded by one deck BaO, and this will control γ-Al effectively
2o
3in the back in liquid-state silicon with SiO
2between solid state reaction;
(3) γ-Al in solid state reaction
2o
3with SiO
2between the mol ratio of 3: 2, according to the γ-Al taking in step (1)
2o
3molar weight, takes appropriate SiO
2powder raw material, then by weighed SiO
2raw material is positioned in ball mill ball milling 6～10 hours;
(4) resulting raw material in step (2) and step (3) is positioned over together in mixer and is mixed 0.5～1.5 hour, because mixer does not have the effect of refinement to feed particles, therefore the size of feed particles can not change in this step, because of γ-Al
2o
3particle is surrounded by one deck BaO, so BaO is at γ-Al
2o
3with SiO
2between powder, form the barrier of a solid phase diffusion, thereby can effectively control the process of solid state reaction;
(5) the resulting slag former particle of step (4) is joined in the liquid-state silicon of melting, the ratio that slag former accounts for siliceous amount is 20%～40%, and the temperature of liquid-state silicon is 1435 ℃, the γ-Al in slag former particle
2o
3with SiO
2start by the solid state reaction generation mullite that reacts, the reaction deadline is relevant with Ball-milling Time with BaO add-on in step (2), it is 2～6 hours, in this step, constantly bottom blowing or top blast rare gas element stir liquid-state silicon, slag former particle is fully contacted with liquid-state silicon, improve gettering efficiency;
(6) after step (5) slag making completes, by liquid-state silicon cooled and solidified, excision slag former, the silicon after being purified.
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| CN110467185B (en) * | 2019-09-10 | 2020-11-10 | 中国科学院合肥物质科学研究院 | Silicon material dephosphorization purification additive and purification method |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101837348A (en) * | 2010-04-28 | 2010-09-22 | 江西赛维Ldk太阳能高科技有限公司 | Method for separating silicon from impurities |
| CN102001661A (en) * | 2010-11-22 | 2011-04-06 | 东海晶澳太阳能科技有限公司 | Method for slagging, boron removal and purification of metalluragical silicon |
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| US8337795B2 (en) * | 2009-08-25 | 2012-12-25 | Process Research Ortech Inc. | Production of high purity silicon from amorphous silica |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101837348A (en) * | 2010-04-28 | 2010-09-22 | 江西赛维Ldk太阳能高科技有限公司 | Method for separating silicon from impurities |
| CN102001661A (en) * | 2010-11-22 | 2011-04-06 | 东海晶澳太阳能科技有限公司 | Method for slagging, boron removal and purification of metalluragical silicon |
Non-Patent Citations (2)
| Title |
|---|
| Effect of slag basicity and oxygen potential on the distribution of boron and phosphorus between slag and silicon;M. D. Johnston et al.;《Journal of Non-Crystalline Solids》;20101126;第357卷;970-975 * |
| M. D. Johnston et al..Effect of slag basicity and oxygen potential on the distribution of boron and phosphorus between slag and silicon.《Journal of Non-Crystalline Solids》.2010,第357卷970-975. |
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