CN101812727B - Method for directionally solidifying and purifying polycrystalline silicon under DC electric field - Google Patents
Method for directionally solidifying and purifying polycrystalline silicon under DC electric field Download PDFInfo
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- CN101812727B CN101812727B CN2010101484259A CN201010148425A CN101812727B CN 101812727 B CN101812727 B CN 101812727B CN 2010101484259 A CN2010101484259 A CN 2010101484259A CN 201010148425 A CN201010148425 A CN 201010148425A CN 101812727 B CN101812727 B CN 101812727B
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Abstract
The invention discloses a method for directionally solidifying and purifying polycrystalline silicon under the action of a DC electric field. In the method, the DC electric field which is parallel to the crystal growth direction is applied to fused silicon solution in the growth process of the polycrystalline silicon directional solidification crystal, so that the impurities rapidly move to the electrode direction under the action of the electric field, namely the cation impurities move to the cathode direction, and the anion impurities move to the anode direction. Therefore, the impurity concentration in the crystal growth terminal liquid phase is effectively reduced and the crystal impurity content of subsequent growth is lowered, and polycrystalline silicon ingots of which the directional solidification purity is higher than that of the traditional method for directionally solidifying and purifying the polycrystalline silicon are obtained.
Description
Technical field
The present invention relates to the purification of polysilicon, specifically be meant a kind of under the DC electric field effect method of directional solidification purified polysilicon.
Background technology
Polysilicon is as the main raw material of crystal-silicon solar cell, and is along with the fast development of photovoltaic industry, increasing to its demand.The main source of tradition solar-grade polysilicon is waste product material such as remaining pot bottom material when producing electronic-grade silicon single crystal, and silicon single crystal ingot cutting swarf.Many shortcomings such as (improvement) Siemens Method is the main method of producing high purity polycrystalline silicon at present, though the polysilicon purity height that this method obtains has energy consumption height, production cost height, scale of investment is big, and the construction period is long.In recent years, along with highlighting day by day of solar-grade polysilicon disparities between supply and demand, and the hope that further reduces production costs, new technology, the novel method of some preparation solar-grade polysilicons have obtained fast development.
In numerous novel procesies of preparation solar-grade polysilicon, directly the metallurgical grade industrial silicon is purified to the main direction that solar level has become present technical study development by the physical metallurgy means, usually the metallurgical technology that adopts comprises that mainly the dephosphorization of electron beam heating, vacuum, plasma heating are except that boron, hydrometallurgy, slag making refining, vacuum refinement, directional freeze etc., because single technology is difficult to make its product purity to reach the solar level requirement, often adopts the combination of several technologies.
Chinese patent application numbers 96198989.0 and 98109237.3 has been introduced a kind of manufacture method of polysilicon, this method at first heats by electron beam under high vacuum, the refining dephosphorization, carry out directional freeze then one time, the part excision that ingot casting top impurity concentration is high, remainder removes boron with the plasma arc oxidation refining, carries out directional freeze again one time, finally obtains solar-grade polysilicon.Japan JFE company adopts similar production technique to set up one and produces 100 tons of demo plants per year.Yet, electron beam heating that this method is used and plasma heating, technical process complexity, apparatus expensive, and energy consumption is big, production cost is higher relatively.
Chinese patent application number a kind of method of producing the used for solar batteries high purity polycrystalline silicon of 02135841.9 proposition, at first adopt slag making purified method, in molten silicon liquid, add the slag former of lime, ferric oxide and fluorite component, aerating oxygen, chlorine or steam-laden hydrogen are removed impurity then, carry out the polysilicon that directional freeze obtains purity 3～5N at last.Chinese patent application numbers 200610017755, with the higher-grade silica is raw material, with the mixture reduction of high-purity refinery coke and coal,, obtain the p type polysilicon of 6～7N then through intermediate frequency (IF) smelting, centrifugal impurity elimination, vibration removal of impurities, electron beam dephosphorization and directional freeze ingot casting.
Directional freeze is a kind of purifying metals and the common method of semiconductor material, and when especially adopting the physical metallurgy method to produce solar-grade polysilicon, directional freeze is often used as the means that last impurity removal process and ingot casting are produced.Because the equilibrium segregation coefficient of most of metallic elements in silicon is very little, when the silicon crystal oriented growth, these impurity elements will be rejected in the liquid phase at solid-liquid interface place, be concentrated into the part of final set along with the crystalline growth.The ingot casting that foreign matter content is high portion and the peripheral part that contacts with crucible end to end cuts, and obtains the higher part of purity, thereby reaches the purpose of purification.Yet some elements, as boron (B), phosphorus (P) etc., the equilibrium segregation coefficient in silicon is near 1, and common directional solidification processes does not almost have refining effect to these impurity, so directional freeze requires raw material to have lower B, P content, this has increased the difficulty of former process greatly.Improve the removal of impurities ability of directional solidification processes, reduce requirement, the production cost of controlling solar-grade polysilicon is played keying action preceding road impurity removal process.
Summary of the invention
In order to strengthen the refining effect of directional solidification processes to polysilicon, the object of the present invention is to provide a kind of method of under the DC electric field effect, carrying out directional solidification purified polysilicon, this method is particularly useful for the purification of high purity polycrystalline silicon and the manufacturing of polycrystal silicon ingot.
Technical scheme of the present invention is in the polysilicon directional freezing crystal growing process, molten silicon liquid is applied a DC electric field parallel with crystal growth direction, impurity is moved to electrode region rapidly under effect of electric field, be that positively charged ion or the impurity with cation effect (below be referred to as cation impurity) move to cathode zone, negatively charged ion or have impurity (below be referred to as anionic impurity) the anode zone migration of anion effect, effectively reduce the impurity concentration in the crystal growth tip liquid phase, make the crystal foreign matter content of subsequent growth lower, obtain than the higher polycrystal silicon ingot of traditional directional freeze purity.
The method of a kind of directionally solidifying and purifying polycrystalline silicon under DC electric field of the present invention, its concrete steps are as follows:
1) at the crucible inner bottom part lower electrode is set, adds the silicon material according to usual method in crucible, in crucible, silicon material top is provided with top electrode then, and inciting somebody to action up and down with lead, two electrodes link to each other with direct supply.Note making direction of an electric field parallel with the crystalline direction of growth during arrangement of electrodes, direction of an electric field is provided with according to the ion characteristic decision of impurity with respect to silicon liquid, when being main to remove cation impurity, makes direction of an electric field identical with crystal growth; When being main, make direction of an electric field opposite with crystal growth direction to remove anionic impurity.
2) charged crucible is placed the furnace chamber well heater, vacuumize in the stove.The attemperation Controlling System makes silicon material heat fused become silicon liquid, adjusts the position of top electrode, makes the liquid level of top electrode and silicon liquid keep good Ohmic contact.
3) molten state of maintenance silicon liquid begins to apply DC electric field, and the voltage of strength of electric field is that 0.1～10V or current density are 0.1～10A/cm
2, make cation impurity and anionic impurity respectively to negative electrode and anode direction migration, and keep static more than 1 hour, allow impurity in the abundant enrichment of electrode region.
4) attemperation Controlling System reduces the temperature of crucible bottom rapidly, allows the silicon liquid rapid solidification in lower electrode zone, makes to be enriched in this regional impurity in the solid solution of crystal camber, and the crystal height of rapid solidification is 5～30mm.
5) attemperation Controlling System is carried out crystal growth with the speed of 5～50mm/h, keeps DC electric field simultaneously, solidifies fully up to silicon liquid.The processing mode of steps such as remaining thermal treatment, cooling is the same with traditional directional freeze casting ingot process.
6) the rapid solidification part of silicon ingot bottom and the impurity concentrating part at top are excised, and the edge section that contacts with crucible of excision, can obtain than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
Adopt technical scheme of the present invention to compare and have following characteristics with traditional directional freeze:
1) do not having under the situation of electric field, impurity is the chaotic distribution state in the molten silicon liquid; And after applying DC electric field, to corresponding electrode direction migration, anionic impurity will be in the anode region enrichment under effect of electric field for all kinds of impurity, and cation impurity will be in the cathode zone enrichment, and those electric neutrality impurity are still state of disarray and distribute, as shown in Figure 1.
2) in the crystal growing process, impurity is discharged in the liquid phase of crystal growth tip under the solidifying segregation effect, and forms enrichment gradually.Do not have electrical forces to do the time spent, the motivating force that the impurity of enrichment mainly relies on concentration gradient is gradually to away from the diffusion of solid-liquid interface place, but because diffusion is slower, and enrichment degree is more and more higher, makes that foreign matter content also raises thereupon gradually in the crystal of subsequent growth; When applying DC electric field, under concentration gradient and electrical forces dual function, the impurity of some enrichments rapidly upwards electrode district migrate, effectively reduce the enrichment degree of impurity in the crystal growth tip liquid phase, thereby make the crystal of subsequent growth have lower foreign matter content.
3) by changing the direction of DC electric field, can strengthen impurity-eliminating effect to specific impurities.When direction of an electric field is identical with crystal growth direction, cation impurity had better impurity-eliminating effect; When direction of an electric field is opposite with crystal growth direction, anionic impurity had better impurity-eliminating effect.
Description of drawings
Fig. 1 be under the DC electric field effect impurity at the synoptic diagram of electrode near zone enrichment;
Fig. 2 be in the ingot casting foreign matter content with ingot casting growing height distribution schematic diagram.
Each label is among the figure: 1 is crucible; 2 is silicon liquid; 3 is anionic impurity; 4 is electric neutrality impurity; 5 is cation impurity; 11 is direct supply; 12 is lead; 1 is 3 anodes; 14 is negative electrode.
Embodiment
Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail:
Be set to example with electric field shown in Figure 1, lower electrode (negative electrode 14) is set in crucible 1 bottom, adds the silicon material, on the silicon material, place top electrode (anode 13) then according to usual method, with lead 12 positive pole of anode 13 with direct supply 11 linked to each other, negative electrode 14 links to each other with negative pole.Note making direction of an electric field parallel with the crystalline direction of growth during arrangement of electrodes, anode 13 and negative electrode 14 adopt high purity graphite to make, and lead 12 adopts high-purity molybdenum filament.
Charged crucible 1 is placed the furnace chamber well heater, vacuumize in the stove or fill protective gas.Silicon material heat fused is become silicon liquid 2, adjust the position of anode 13, make the anode 13 and the liquid level of silicon liquid 2 keep good Ohmic contact.
Keep the molten state of silicon liquid 2, begin to apply DC electric field, interelectrode voltage is 0.1～10V or current density to 0.1～10A/cm
2, cation impurity 5 and anionic impurity 3 are moved to the direction of negative electrode 14 and anode 13 respectively, and keep static more than 1 hour, allow impurity in the abundant enrichment of electrode region.
The attemperation Controlling System reduces the temperature of crucible 1 bottom rapidly, allows the silicon liquid rapid solidification in negative electrode 14 zones, makes to be enriched in the crystal camber solid solution of this regional cation impurity 5 at rapid solidification that the crystal height of rapid solidification is 5～30mm.
Subsequently, the attemperation Controlling System is carried out crystal growth with the speed of 5～50mm/h, keeps DC electric field simultaneously, solidifies fully up to silicon liquid 2.
The polycrystal silicon ingot that adopts present embodiment to obtain, the concentration distribution of impurity can be divided into three different zones (I, II and III zone) on crystal growth direction, as shown in Figure 2.
Area I: the initial stage impurity concentration of crystal growth is higher, cation impurity was enriched near the negative electrode before crystal began growth, along with crystal begins growth from the bottom, under the dual function of solidifying segregation and electric field, the concentration of cation impurity sharply raises in the crystal growth tip liquid phase, make peak value of impurity concentration appearance in the crystal, this mainly is by due to a large amount of solid solutions of cation impurity;
Area I I: the intermediate stage impurity concentration of crystal growth is lower, because the anionic impurity that this moment, solidifying segregation was discharged, anode migration rapidly, enrichment under the effect of electrical forces, effectively reduce the impurity concentration in the crystal growth tip liquid phase, so low when the ratio of the foreign matter content in the crystal does not have electric field action.
Area I II: the ending phase impurity concentration of crystal growth is very high, impurity concentration near anode the time in the minimizing of residual solution phase volume, the crystal growth tip liquid phase skyrockets, make the foreign matter content in the crystal sharply raise, but mainly be due to a large amount of solid solutions of anionic impurity and electric neutrality impurity this moment.
According to the regularity of distribution of foreign matter content in the polycrystalline silicon ingot casting, high two ends (area I and area I II) up and down of excision foreign matter content, and the edge section that contacts with crucible can obtain than the higher polycrystal silicon ingot of traditional directional freeze purity.Be not difficult to find, according to the polycrystal silicon ingot that technical scheme of the present invention obtains, not only whole purity height, and also impurities concentration distribution is even, and the qualification rate of product also rises to some extent.
Above-described embodiment is only in order to illustrate technological thought of the present invention and characteristics; its purpose is to make those of ordinary skill in the art can understand content of the present invention and implements according to this; scope of the present invention also not only is confined to above-mentioned specific embodiment; be all equal variation or modifications of doing according to disclosed spirit, still be encompassed in protection scope of the present invention.
Claims (1)
1. the method for a directional solidification purified polysilicon under the DC electric field effect is characterized in that concrete steps are as follows:
1) at the crucible inner bottom part lower electrode is set, the silicon material is tiled in the crucible on the lower electrode, above the silicon material, top electrode is set then, with lead up and down two electrodes link to each other with direct supply; Note making direction of an electric field parallel with the crystalline direction of growth during arrangement of electrodes, the polarity of upper/lower electrode is provided with according to the ion characteristic decision of impurity with respect to silicon liquid;
2) charged crucible is placed the furnace chamber well heater, vacuumize in the stove; The attemperation Controlling System makes silicon material heat fused become silicon liquid, adjusts the position of top electrode, makes the liquid level of top electrode and silicon liquid keep good Ohmic contact;
3) molten state of maintenance silicon liquid begins to apply DC electric field, and interelectrode voltage is that 0.1～10V or current density are 0.1～10A/cm
2, make cation impurity and anionic impurity respectively to negative electrode and anode direction migration, and keep static more than 1 hour, allow impurity in the abundant enrichment of electrode region;
4) attemperation Controlling System reduces the temperature of crucible bottom rapidly, allows the silicon liquid rapid solidification in lower electrode zone, makes the impurity that is enriched in the lower electrode zone in the solid solution of crystal camber, and the crystal height of rapid solidification is 5～30mm;
5) attemperation Controlling System is carried out crystal growth with the speed of 5～50mm/h, keeps DC electric field simultaneously, solidifies fully up to silicon liquid; Follow-up thermal treatment, cooling process mode are the same with traditional directional freeze casting ingot process;
6) the rapid solidification part of silicon ingot bottom and the impurity concentrating part at top are excised, and the edge section that contacts with crucible of excision, can obtain than the higher polycrystal silicon ingot of traditional directional freeze purity.
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| CN102094238A (en) * | 2010-09-28 | 2011-06-15 | 常州天合光能有限公司 | Method for reducing internal stress defect of ingot polycrystal |
| CN102703985A (en) * | 2012-06-26 | 2012-10-03 | 上海太阳能电池研究与发展中心 | Method for preparing high-purity polycrystalline silicon under action of electric field and fused salt |
| CN104495853B (en) * | 2014-12-05 | 2016-04-13 | 青海大学 | A kind of industrial silicon refining method |
| CN107164802A (en) * | 2017-04-12 | 2017-09-15 | 济南大学 | A kind of method that electrostatic field aids in polycrystalline silicon ingot casting |
| CN112108086B (en) * | 2020-09-24 | 2022-06-21 | 上海理工大学 | Directional solidification segregation device and method for colloidal particle system |
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| JP4151148B2 (en) * | 1999-02-19 | 2008-09-17 | 株式会社Ｓｕｍｃｏ | Method for producing silicon single crystal |
| CN1241270C (en) * | 2002-11-26 | 2006-02-08 | 郑智雄 | High-purity silicon for solar energy cell and production method thereof |
| CN100444410C (en) * | 2006-05-08 | 2008-12-17 | 高文秀 | P-type solar cell grade polycrystalline silicon preparing process |
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