CN102703985A - Method for preparing high-purity polycrystalline silicon under action of electric field and fused salt - Google Patents
Method for preparing high-purity polycrystalline silicon under action of electric field and fused salt Download PDFInfo
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- CN102703985A CN102703985A CN2012102142633A CN201210214263A CN102703985A CN 102703985 A CN102703985 A CN 102703985A CN 2012102142633 A CN2012102142633 A CN 2012102142633A CN 201210214263 A CN201210214263 A CN 201210214263A CN 102703985 A CN102703985 A CN 102703985A
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Abstract
The invention discloses a method for preparing high-purity polycrystalline silicon under the action of electric field and fused salt. The method specially comprises the steps that: in the growth process of directionally condensed crystals of polycrystalline silicon, a fused salt layer is arranged between a silicon solution and an electrode so as to separate the electrode from the silicon solution, impurities in the silicon solution fast shift towards the electrode under the action of the electric field, and can react with fused salt so as to be absorbed when arriving at the boundary of the fused salt and the silicon solution, and the fused salt layer protects the electrode from being corroded by the silicon solution. By the method, not only can the electrode be prevented from being polluted by the silicon solution, but also the impurity removal capability of the directional solidification process and the utilization rate of a silicon ingot can be improved.
Description
Technical field
The present invention relates to the preparation of high purity polycrystalline silicon material, specifically be meant a kind of method that under electric field and fused salt effect, prepares high purity polycrystalline silicon.
Background technology
Polysilicon is as the main raw material of silica-based solar cell, and is along with the fast development of photovoltaic industry, increasing to its demand.(improvement) Siemens Method is the main method of producing high purity polycrystalline silicon at present, though the polysilicon purity that this method obtains is high, high, the deficiencies such as production cost is high, contaminate environment, scale of investment is big, the construction period is long of energy consumption is arranged.In order further to reduce production costs, in recent years, new technology, the novel method of some preparation solar-grade polysilicons have obtained fast development.In numerous novel procesies; Directly the metallurgical grade industrial silicon is purified to the main direction that solar level has become present technical study development through the physical metallurgy means; Because single metallurgical technology is difficult to make its product purity to reach the solar level requirement, adopt the combination of several kinds of technologies to reach the effect of purification usually.
Directional freeze is a kind of domestic method of purifying metals with semiconductor material, and when especially adopting metallurgy method to produce solar-grade polysilicon, directional freeze is used as the last impurity removal process and the means of ingot production usually.Because the equilibrium segregation coefficient of most metal element 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; Like 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.
Having introduced the method for purifying polycrystalline silicon under a kind of electric field action among the japanese patent laid-open 6-206719, specifically is that two electrodes are inserted in the molten silicon liquid, and the impurity in the silicon melt of energising back receives electric field action, and anode and cathode zone are assembled respectively; Behind the certain hour; Two electrodes of cool quickly solidify near the silicon liquid of the enrichment impurity of electrode on electrode, take out electrode; B and P can reduce to the degree of 5ppm from 30ppm, have good impurity-eliminating effect.Though this kind method can reach the purpose of purification to a certain extent, complicated operation under the hot conditions can only carry out on small test device, can't realize the successive suitability for industrialized production, and production efficiency is low.One Chinese patent application numbers 20101014825.9 propose a kind of under the DC electric field effect method of directional solidification purified polysilicon; 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 direction rapidly under electric field action, obtain than the higher polycrystal silicon ingot of traditional directional freeze purity.This method is fit to large-scale production, but Graphite Electrodes directly contacts with silicon liquid, is prone to react with molten silicon liquid, is difficult to avoid the impurity in the electrode to get into silicon liquid, thereby influences refining effect.
Summary of the invention
In order to address the above problem, the present invention combines the advantage separately of electric field and the effect of fused salt gettering, has proposed to prepare under a kind of electric field and the fused salt effect method of high purity polycrystalline silicon.
Technical scheme of the present invention is in the crystal growing process of polysilicon directional freezing; At silicon liquid electrode is set up and down; And with the different molten salt layer of density electrode and silicon liquid are separated, the impurity under electric field action in the silicon liquid moves rapidly to electrode direction, when arriving the interface of fused salt and silicon liquid; React with fused salt and absorbed, the molten salt layer protection that is melted of electrode simultaneously and not by the silicon corrosion by fused salt.
A kind of electric field of the present invention and fused salt effect prepare the method for high purity polycrystalline silicon down, and its step is following:
§ 1. molten salt preparation
Fused salt is sodium, potassium, calcium, magnesium, the oxide compound of barium element, muriate, fluorochemical, oxyhydroxide, carbonate, supercarbonate, and Si
3N
4, SiO
2, Al
2O
3In one or more combination, the fused salt after the combination will satisfy following requirement:
Fusing point will be lower than fusing point (1420 ℃) and the boiling point of the silicon fusing point (1420 ℃) greater than silicon, and guaranteeing that molten salt layer can separate Graphite Electrodes and silicon liquid effectively when the silicon material melts, and fused salt can not volatilize in the fusing of silicon material and crystal growing process in a large number;
The density of fused salt is greater than the density of silicon liquid or less than the density of silicon liquid, silicon liquid density is 2.533g/cm
3, density is called little density fused salt than the little fused salt of silicon liquid density, and the fused salt that density is bigger than silicon liquid is called big density fused salt.
The mass ratio of fused salt consumption and silicon material consumption is 3: 2-1: between 20, in order in certain crucible volume, to improve the add-on of silicon material, under the prerequisite that guarantees abundant absorption impurity, reduce the fused salt consumption as far as possible.
§ 2. is arranged on the growth of the high purity polycrystalline silicon of silicon liquid top and bottom for electrode
(a). set gradually dull and stereotyped lower electrode, big density fused salt, silicon material at the crucible inner bottom part.Dull and stereotyped top electrode links to each other with direct supply with two electrodes about the lead general with the height of a mechanical lifting gear control electrode in crucible, notes making direction of an electric field parallel with the crystalline direction of growth during arrangement of electrodes.
(b). charged crucible is placed the furnace chamber well heater, vacuumize in the stove or fill protective atmosphere; The attemperation system, treat big density fused salt and silicon material heat fused after, through feeding device little density fused salt is added on the melted silicon material in the crucible; The attemperation gear makes fused salt and silicon material keep molten state; Regulate the lifting device of top electrode, make top electrode decline and keep good Ohmic contact with little density fused salt.
(c). begin to apply DC electric field, current density is 0.01～50A/cm
2, make cation impurity and anionic impurity respectively to the migration of negative electrode and anode direction, when arriving the interface of fused salt and silicon liquid, react with fused salt and absorbed by fused salt; DC electric field keeps after the 0.5-1h, and the attemperation system is carried out crystal growth with the speed of 5～50mm/h then, keeps DC electric field simultaneously, solidifies fully up to silicon liquid.
(d). the processing mode of steps such as follow-up thermal treatment, cooling is the same with traditional directional freeze casting ingot process.
(e). up and down molten salt layer separates with silicon ingot at last, and the edge section that contacts with crucible of the edge section that contacts with molten salt layer with the top bottom the excision silicon ingot and sidepiece, can obtain than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
§ 3. is arranged on the growth of the high purity polycrystalline silicon above the silicon liquid for electrode
(a). be arranged on above the silicon liquid earlier with in the silicon material adding crucible for electrode; With insulation barrier silicon material in the crucible is divided into two zones; The degree of depth that insulation barrier stretches into the silicon material will guarantee that liquid level after the fusion of silicon material is higher than the lower rim 5-10mm of insulating barrier; In two zones, add little density fused salt subsequently respectively, plate electrode is set respectively above fused salt, and link to each other with the positive and negative electrode of direct supply respectively through lead.
(b). charged crucible is placed the furnace chamber well heater; Vacuumize in the stove or fill protective atmosphere, the attemperation system, treat fused salt and silicon material heat fused after; Regulate the lifting device of plate electrode, make plate electrode decline and keep good Ohmic contact with little density fused salt.
(c). begin to apply DC electric field, current density is 0.01～50A/cm
2, after DC electric field kept 1h, the attemperation system was carried out crystal growth with the speed of 5～50mm/h, and DC electric field is maintained until silicon liquid and solidifies fully.
(d). the processing mode of steps such as follow-up thermal treatment, cooling is the same with traditional directional freeze casting ingot process.
(e). at last molten salt layer and silicon ingot are separated, and the excision edge section that contacts with molten salt layer of silicon ingot and the edge section that contacts with crucible, can obtain than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
Equally also can adopt plate electrode is arranged on below the silicon liquid, adopt the growth pattern of the high purity polycrystalline silicon of big density fused salt, also can obtain the high purity polycrystalline silicon ingot casting.
Adopt technical scheme of the present invention to have the following advantages:
1) after adding molten salt layer between silicon material and the electrode, the fusion molten salt layer is effectively isolated silicon liquid and Graphite Electrodes, prevents that Graphite Electrodes from directly contacting with silicon liquid, has avoided the impurity in the electrode to get into silicon liquid.
2) impurity in the silicon liquid moves rapidly to electrode direction under electric field action, when arriving the interface of fused salt and silicon liquid, can react with fused salt and be absorbed, and can effectively reduce the impurity concentration in the silicon liquid, strengthens the impurity-eliminating effect of directional freeze process.
3) in the directional freeze process; With crystal growth gradually the impurity of enrichment under electric field action; Be enriched at last in the molten salt layer, therefore only need excision silicon ingot bottom to get final product, can reduce the silicon ingot resection length, increase operation rate with the edge that the top contacts with molten salt layer.
Description of drawings
Fig. 1 is separately positioned on the structural representation of the high purity polycrystalline silicon growth pattern of silicon liquid top and bottom for planar cathode electrode and dull and stereotyped anode electrode;
Fig. 2 is separately positioned on the structural representation of the high purity polycrystalline silicon growth pattern in two zones above the silicon liquid for planar cathode electrode and dull and stereotyped anode electrode.
Embodiment
Do further to specify below in conjunction with the accompanying drawing specific embodiments of the invention:
The interpolation fused salt mode that embodiment 1 is as shown in Figure 1 is provided with planar cathode electrode 9 at crucible 1 inner bottom part, in crucible, adds the big density fused salt 4 of 2.4Kg subsequently, and it is 3: 3: 4 CaO-SiO that big density fused salt adopts mass ratio
2-CaF
2, above fused salt, add 10Kg silicon material 2 again.Above silicon material 2, leave silicon material surface one segment distance dull and stereotyped anode electrode 8 is set, dull and stereotyped anode electrode position can be regulated (in Fig. 1, not drawing) by lifting device.With lead 6 dull and stereotyped anode electrode 8 is linked to each other with the positive pole of direct supply 7, planar cathode electrode 9 links to each other with negative pole.Dull and stereotyped anode electrode 8 adopts high purity graphite to process with dull and stereotyped cathode electrode 9, and lead 6 adopts high-purity molybdenum filament.Note making direction of an electric field parallel during arrangement of electrodes with the crystalline direction of growth.
Charged crucible 1 is placed the furnace chamber well heater, vacuumize in the stove or protective atmosphere.The attemperation system makes big density fused salt 4 and silicon material 2 heat fused, above silicon liquid, adds the little density fused salt 3 of 2.3Kg through feeding device then, and little density fused salt employing mass ratio is 2: 3 CaCl
2-KCl.The attemperation gear makes CaCl
2-KCl fused salt 3 heating and melting, and keep the molten state of big density fused salt 4 and silicon material.Regulate electrode lifting device, make dull and stereotyped anode electrode 8 and CaCl
2-KCl fused salt 3 liquid levels keep good Ohmic contact.
Begin to apply DC electric field, current density is 0.1A/cm
2, apply DC electric field 1h after, the attemperation system is carried out crystal growth with the speed of 10mm/h then, 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.
Up and down molten salt layer separates with silicon ingot, and the edge section that contacts with crucible of the edge section that contacts with molten salt layer of excision silicon ingot bottom and top and sidepiece, and acquisition is than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
Embodiment 2: with interpolation fused salt mode shown in Figure 1, big density fused salt 4 employing mass ratioes are 17: 2: 1 SiO
2-Al
2O
3-K
2O, add-on is 2.4Kg, little density fused salt 3 employing mass ratioes are 1: 6: 4 Si
3N
4-KCl-MgCl
2, add-on is 2.5Kg, and silicon material add-on is 10Kg, and all the other steps are with embodiment 1.
Embodiment 3: the interpolation fused salt mode with shown in Figure 1 is an example, and big density fused salt 4 employing mass ratioes are 10: 3: 4 BaCO
3-SiO
2-MgF
2, add-on is 2.6Kg, little density fused salt 3 employing mass ratioes are 3: 4: 3 SiO
2-NaHCO
3-KCl.Add-on is 2.4Kg, and silicon material add-on is 10Kg, and all the other steps are with embodiment 1.Embodiment 2 and embodiment 3 also obtain the high purity polycrystalline silicon ingot casting.
Embodiment 4: the interpolation fused salt mode with shown in Figure 2 is an example; Earlier 10Kg silicon material 2 is added in the crucible 1; With insulation barrier 5 silicon material in the crucible is divided into two zones again; Liquid level was higher than insulating barrier lower rim 7m m after the degree of depth that insulation barrier stretches into the silicon material guaranteed the fusion of silicon material, in two zones, added little density fused salt 3 subsequently respectively, and it is 2: 1: 2 SiO that little density fused salt 3 adopts mass ratioes
2-Na
2O-KCl, add-on is 4.5Kg, and dull and stereotyped anode electrode 8 and dull and stereotyped cathode electrode 9 are set respectively above the fused salt in two zones, and links to each other with the positive and negative electrode of direct supply 7 respectively through lead 6.Dull and stereotyped anode electrode 8 adopts high purity graphite with dull and stereotyped cathode electrode 9, and lead 6 adopts high-purity molybdenum filament.
Charged crucible 1 is placed the furnace chamber well heater, vacuumize in the stove or protective atmosphere.The attemperation system, and heat temperature raising makes little density fused salt 3 and 2 fusings of silicon material, regulates electrode height, makes dull and stereotyped anode electrode 8 and dull and stereotyped cathode electrode 9 and little density fused salt 3 liquid levels keep good Ohmic contact.
Begin to apply DC electric field, current density is 0.1A/cm
2, behind maintenance 1h conduction time, the attemperation system is carried out crystal growth with the speed of 10mm/h, keeps DC electric field to silicon liquid and solidifies fully.The processing mode of steps such as remaining thermal treatment, cooling is the same with traditional directional freeze casting ingot process.
Molten salt layer and silicon ingot are separated, and the excision edge section that contacts with molten salt layer of silicon ingot and the edge section that contacts with crucible, acquisition is than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
Embodiment 5: the interpolation fused salt mode with shown in Figure 2 is an example, and the employing mass ratio is 3: 2: 3 SiO
2The little density fused salt of-NaOH-KCl, add-on is 4.7Kg, silicon material add-on is 10Kg.All the other steps are with embodiment 4.
Embodiment 6: the interpolation fused salt mode with shown in Figure 2 is an example, and the employing mass ratio is 6: 5: 6 SiO
2-Na
2CO
3The little density fused salt of-KCl, add-on is 4.6Kg, silicon material add-on is 10Kg.All the other steps are with embodiment 4.Embodiment 5 and embodiment 6 also obtain the high purity polycrystalline silicon ingot casting.
Above-described embodiment has been merely explanation 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 (2)
1. electric field and fused salt effect prepare the method for high purity polycrystalline silicon down, it is characterized in that step is following:
§ A. molten salt preparation
Fused salt is sodium, potassium, calcium, magnesium, the oxide compound of barium element, muriate, fluorochemical, oxyhydroxide, carbonate, supercarbonate, and Si
3N
4, SiO
2, Al
2O
3In one or more combination, the fused salt after the combination will satisfy following requirement:
The fused salt fusing point will be lower than the fusing point of silicon, and boiling point is greater than the fusing point of silicon, and the fusing point of silicon is 1420 ℃;
The density of fused salt is greater than the density of silicon liquid or less than the density of silicon liquid, silicon liquid density is 2.533g/cm
3, density is called little density fused salt than the little fused salt of silicon liquid density, and the fused salt that density is bigger than silicon liquid is called big density fused salt;
The mass ratio of fused salt consumption and silicon material consumption is 3: 2-1: between 20;
§ B. is arranged on the growth of the high purity polycrystalline silicon of silicon liquid top and bottom for electrode
A. set gradually dull and stereotyped lower electrode, big density fused salt, silicon material at the crucible inner bottom part; Dull and stereotyped top electrode is with the height of a mechanical lifting gear control electrode in crucible; Link to each other with direct supply with two electrodes about the lead general, note making direction of an electric field parallel during arrangement of electrodes with the crystalline direction of growth;
B. charged crucible is placed the furnace chamber well heater, vacuumize in the stove or fill protective atmosphere; The attemperation system, treat big density fused salt and silicon material heat fused after, through feeding device little density fused salt is added on the melted silicon material in the crucible; The attemperation gear makes fused salt and silicon material keep molten state; Regulate the lifting device of top electrode, make top electrode decline and keep good Ohmic contact with little density fused salt;
C. begin to apply DC electric field, current density is 0.01～50A/cm
2, make cation impurity and anionic impurity respectively to the migration of negative electrode and anode direction, when arriving the interface of fused salt and silicon liquid, react with fused salt and absorbed by fused salt; DC electric field keeps after the 0.5h, and the attemperation system is carried out crystal growth with the speed of 5～50mm/h then, keeps DC electric field simultaneously, solidifies fully up to silicon liquid;
The processing mode of steps such as d. follow-up thermal treatment, cooling is the same with traditional directional freeze casting ingot process;
E. at last up and down molten salt layer separate with silicon ingot, and the edge section that contacts with crucible of the edge section that contacts with molten salt layer with the top bottom the excision silicon ingot and sidepiece can obtain than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
2. electric field and fused salt effect prepare the method for high purity polycrystalline silicon down, it is characterized in that step is following:
§ A. molten salt preparation
Fused salt is sodium, potassium, calcium, magnesium, the oxide compound of barium element, muriate, fluorochemical, oxyhydroxide, carbonate, supercarbonate, and Si
3N
4, SiO
2, Al
2O
3In one or more combination, the fused salt after the combination will satisfy following requirement:
The fused salt fusing point will be lower than the fusing point of silicon, and boiling point is greater than the fusing point of silicon, and the fusing point of silicon is 1420 ℃;
The density of fused salt is greater than the density of silicon liquid or less than the density of silicon liquid, silicon liquid density is 2.533g/cm
3, density is called little density fused salt than the little fused salt of silicon liquid density, and the fused salt that density is bigger than silicon liquid is called big density fused salt;
The mass ratio of fused salt consumption and silicon material consumption is 3: 2-1: between 20;
§ B. is arranged on the growth of the high purity polycrystalline silicon above the silicon liquid for electrode
A. earlier the silicon material is added in the crucible; With insulation barrier silicon material in the crucible being divided equally is two zones; The degree of depth that insulation barrier stretches into the silicon material will guarantee that liquid level after the fusion of silicon material is higher than the lower limb 5-10mm of insulating barrier; In two zones, add little density fused salt subsequently respectively; Plate electrode is set respectively above fused salt, and links to each other with the positive and negative electrode of dc source respectively by lead;
B. charged crucible is placed the furnace chamber well heater; Vacuumize in the stove or fill protective atmosphere, the attemperation system, treat fused salt and silicon material heat fused after; Regulate the lifting device of plate electrode, make plate electrode decline and keep good Ohmic contact with little density fused salt;
C. begin to apply DC electric field, current density is 0.01～50A/cm
2, after DC electric field kept 1h, the attemperation system was carried out crystal growth with the speed of 5～50mm/h, and DC electric field is maintained until silicon liquid and solidifies fully;
The processing mode of steps such as d. follow-up thermal treatment, cooling is the same with traditional directional freeze casting ingot process;
E. at last molten salt layer and silicon ingot are separated, and the excision edge section that contacts with molten salt layer of silicon ingot and the edge section that contacts with crucible, can obtain than the higher polycrystalline silicon ingot casting of traditional directional freeze purity.
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| CN104724704A (en) * | 2015-03-18 | 2015-06-24 | 中国科学院过程工程研究所 | Method for refining and purifying silicon alloy from electric field-enhanced molten slag |
| CN112553479A (en) * | 2020-12-04 | 2021-03-26 | 清远先导材料有限公司 | Method for removing high-purity antimony surface pollutants |
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| CN112553479A (en) * | 2020-12-04 | 2021-03-26 | 清远先导材料有限公司 | Method for removing high-purity antimony surface pollutants |
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