WO1989002415A1 - Method for the purification of silicon - Google Patents

Method for the purification of silicon Download PDF

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Publication number
WO1989002415A1
WO1989002415A1 PCT/SE1988/000469 SE8800469W WO8902415A1 WO 1989002415 A1 WO1989002415 A1 WO 1989002415A1 SE 8800469 W SE8800469 W SE 8800469W WO 8902415 A1 WO8902415 A1 WO 8902415A1
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WO
WIPO (PCT)
Prior art keywords
slag
silicon
weight
alkali
earth metals
Prior art date
Application number
PCT/SE1988/000469
Other languages
French (fr)
Inventor
Rolf MELLSTRÖM
Olaus Andersson
Göran ÅHLUND
Ingemar Johansson
Original Assignee
Kemanord Industrikemi Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kemanord Industrikemi Ab filed Critical Kemanord Industrikemi Ab
Priority to BR888807699A priority Critical patent/BR8807699A/en
Publication of WO1989002415A1 publication Critical patent/WO1989002415A1/en
Priority to NO901150A priority patent/NO901150D0/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/037—Purification

Definitions

  • the present invention relates to a method for the purification of silicon. More particularly, the inven ⁇ tion comprises a method for purifying metallurgical si ⁇ licon for the production of raw materials for the semi- conductor and solar cell industry.
  • U.S. patent specification 4,304,763 discloses a multiple step method for purifying metallurgical sili ⁇ con. Finely divided silicon is leached with acid, whereupon it is melted and subjected to vacuum evapo ⁇ ration at 1500°-1700°C. If there is a high content of contaminating boron, molten silicon is contacted with a molten slag which may consist of a mixture of CaF ⁇ , CaO and Si0 2 .
  • Solar cell silicon is defined by its property of converting light energy with an efficiency of at least 10%. Foreign elements affect the efficiency different ⁇ ly. Producers of solar cell silicon have especially wished for a boron reduction to 1-5 pp w in the start ⁇ ing material, and this has not been possible with the prior art techniques referred to above.
  • the present invention as defined by the claims indicates an improved method for the purification of silicon from boron by treating crude silicon with a molten slag. This method gives a higher degree of purification and utilises a less poisonous melt than the above-mentioned method.
  • a further advantage is that the amount of slag-forming agents employed is considerably lower than in prior art methods. For ex- ample, the above-mentioned U.S. patent uses an amount of slag which is twice as large as the amount of sili ⁇ con that is being processed.
  • Solid chlorine compounds are used as the active slag-forming component.
  • chlorides of alkali and/or alkaline earth metals may be used, such as sodium, potassium or lithium chloride, or calcium, magnesium, barium or strontium chloride.
  • Other conceivable solid chlorine compounds are hypo- chlorites, chlorates or perchlorates of alkali and/or alkaline earth metals.
  • constituents of the slag which may be pre ⁇ sent are oxides of alkali and/or alkaline earth metals, and silica. Further constituents that can be used are oxide-forming carbonates and hydroxides of alkali and alkaline earth metals.
  • the slag-forming agent has essentially three functions. It constitutes the extraction phase, i.e. some impurities pass from the silicon phase into the slag phase. It eliminates losses in the form of heat as well as losses in the form of silicon, the latter being caused by splashes from the silicon surface and oxidation thereof.
  • the active component binds boron in the form of volatile boron chlorides.
  • the slag is oxidising in the electrochemical sense, which increases the valency of boron from 0 to +11I, thus facilitating the formation of B(III)chlorides.
  • the method is preferably carried out such that silicon is melted and heated to 1500-1600°C in a melt- ing furnace, whereupon the slag-forming agent is added.
  • the particle size of the slag-forming agent is not critical, but less fumes and less dust are obtained if coarser materials are used. A suitable particle size lies within the range 1-3 mm.
  • the slag- forming agent may be added in one or several runs. After the slag has been added, the melt is again heat- 5 ed to 1500-1600°C. Normally, no longer contact time is required. After the desired number of slag treat ⁇ ments- has been carried out, the silicon is teemed, crushed and allowed to cool and then analysed.
  • the silicon need not first be finely ground and mixed 1.0 with the slag-forming agent and then heated, as indi ⁇ cated by other prior art methods.
  • the method is there ⁇ fore suitable for purifying liquid metallurgical sili ⁇ con directly after a reduction furnace.
  • the slag treatment may take place in a conven- 15 tional melting furnace, for example in an arc furnace or an induction furnace.
  • the furnace is important to the process in so far as it increases the temperature of the material to be processed to a suitable process ⁇ ing temperature. 0
  • the temperature is an important parameter of the purification process. High temperature means high puri ⁇ fication, whereas low temperature gives no purification.
  • a suitable processing temperature is from 1410°C, pre ⁇ ferred temperatures lying between 1500°C and 1600°C. 5 The higher the temperature, the higher will be the pu ⁇ rification efficiency, the upper limit being set by production engineering factors.
  • the quantity ratio between slag and crude silicon based on weight may be 0.1-2, preferably 0.5-1.
  • the com- 0 position of the slag suitably is 0.1-50% by weight of solid chlorine compounds, 0-50% by weight of at least one compound selected from the group consisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals, and 0-80% by weight of silica.
  • Preferred 5 values are 10-30% by weight of solid chlorine compounds, 10-30% by weight of at least one compound selected from the group consisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals, and 40-70% by weight of silica.
  • the values most pre ⁇ ferred are 20, 20 and 60% by weight, respectively.
  • the melt in the furnace consists of two phases, a lower silicon phase and an upper slag phase.
  • the slag is a top slag. To be able to separate the silicon from the slag, it may be necessary to allow the slag to cool somewhat to cause it to set.
  • the silicon obtained by the method according to the invention has a far higher degree of purification than silicon purified by prior art techniques employ ⁇ ing slag purification.
  • the boron content, in particu- lar can be lowered from about 16 ppmw to about 5 ppmw. It has also been found that a considerable purifi ⁇ cation of the carbon content is achieved.
  • the purifica ⁇ tion of carbon is especially advantageous if performed in an arc furnace. In an induction furnace, silicon is contaminated by carbon from the graphite lining. How ⁇ ever, in order to achieve an especially high degree of purification for the remaining impurities, it is neces ⁇ sary to couple the method according to the invention with a known acid and/or vacuum treatment. The invention will now be described in more detail in the following Examples. Example 1

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicon Compounds (AREA)

Abstract

The invention concerns a method for purifying silicon from boron by treating crude silicon with molten slag. Silicon is contacted with a slag, the slag-forming components of which consist of solid chlorine compounds and at least one compound selected from the group consisting of oxides, hydroxides, carbonates of alkali and/or alkaline earth metals as well as silica. Chlorides of alkali and/or alkaline earth metals can be used as solid chlorine compound.

Description

METHOD FOR THE PURIFICATION OF SILICON
The present invention relates to a method for the purification of silicon. More particularly, the inven¬ tion comprises a method for purifying metallurgical si¬ licon for the production of raw materials for the semi- conductor and solar cell industry.
To make the electric energy produced by solar cells economically competitive, the silicon from which the so¬ lar cells are made must be relatively inexpensive. In the production of silicon for electronics components, purification by gaseous phase is used. This technique is far too expensive for the production of solar cells. How¬ ever, since the purity requirements placed on solar cell silicon are not as high as for silicon for electronic uses, simpler purification techniques can be used. U.S. patent specification 4,304,763 discloses a multiple step method for purifying metallurgical sili¬ con. Finely divided silicon is leached with acid, whereupon it is melted and subjected to vacuum evapo¬ ration at 1500°-1700°C. If there is a high content of contaminating boron, molten silicon is contacted with a molten slag which may consist of a mixture of CaF~, CaO and Si02.
Solar cell silicon is defined by its property of converting light energy with an efficiency of at least 10%. Foreign elements affect the efficiency different¬ ly. Producers of solar cell silicon have especially wished for a boron reduction to 1-5 pp w in the start¬ ing material, and this has not been possible with the prior art techniques referred to above. The present invention as defined by the claims indicates an improved method for the purification of silicon from boron by treating crude silicon with a molten slag. This method gives a higher degree of purification and utilises a less poisonous melt than the above-mentioned method. A further advantage is that the amount of slag-forming agents employed is considerably lower than in prior art methods. For ex- ample, the above-mentioned U.S. patent uses an amount of slag which is twice as large as the amount of sili¬ con that is being processed.
Solid chlorine compounds are used as the active slag-forming component. As solid chlorine compounds, chlorides of alkali and/or alkaline earth metals may be used, such as sodium, potassium or lithium chloride, or calcium, magnesium, barium or strontium chloride. Other conceivable solid chlorine compounds are hypo- chlorites, chlorates or perchlorates of alkali and/or alkaline earth metals.
Other constituents of the slag which may be pre¬ sent are oxides of alkali and/or alkaline earth metals, and silica. Further constituents that can be used are oxide-forming carbonates and hydroxides of alkali and alkaline earth metals.
The slag-forming agent has essentially three functions. It constitutes the extraction phase, i.e. some impurities pass from the silicon phase into the slag phase. It eliminates losses in the form of heat as well as losses in the form of silicon, the latter being caused by splashes from the silicon surface and oxidation thereof.
The active component binds boron in the form of volatile boron chlorides. The slag is oxidising in the electrochemical sense, which increases the valency of boron from 0 to +11I, thus facilitating the formation of B(III)chlorides.
The method is preferably carried out such that silicon is melted and heated to 1500-1600°C in a melt- ing furnace, whereupon the slag-forming agent is added. The particle size of the slag-forming agent is not critical, but less fumes and less dust are obtained if coarser materials are used. A suitable particle size lies within the range 1-3 mm. The slag- forming agent may be added in one or several runs. After the slag has been added, the melt is again heat- 5 ed to 1500-1600°C. Normally, no longer contact time is required. After the desired number of slag treat¬ ments- has been carried out, the silicon is teemed, crushed and allowed to cool and then analysed. Thus, the silicon need not first be finely ground and mixed 1.0 with the slag-forming agent and then heated, as indi¬ cated by other prior art methods. The method is there¬ fore suitable for purifying liquid metallurgical sili¬ con directly after a reduction furnace.
The slag treatment may take place in a conven- 15 tional melting furnace, for example in an arc furnace or an induction furnace. The furnace is important to the process in so far as it increases the temperature of the material to be processed to a suitable process¬ ing temperature. 0 The temperature is an important parameter of the purification process. High temperature means high puri¬ fication, whereas low temperature gives no purification. A suitable processing temperature is from 1410°C, pre¬ ferred temperatures lying between 1500°C and 1600°C. 5 The higher the temperature, the higher will be the pu¬ rification efficiency, the upper limit being set by production engineering factors.
The quantity ratio between slag and crude silicon based on weight may be 0.1-2, preferably 0.5-1. The com- 0 position of the slag suitably is 0.1-50% by weight of solid chlorine compounds, 0-50% by weight of at least one compound selected from the group consisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals, and 0-80% by weight of silica. Preferred 5 values are 10-30% by weight of solid chlorine compounds, 10-30% by weight of at least one compound selected from the group consisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals, and 40-70% by weight of silica. The values most pre¬ ferred are 20, 20 and 60% by weight, respectively. After addition of the slag-forming agent and heating for the desired period of time, the melt in the furnace consists of two phases, a lower silicon phase and an upper slag phase. Thus, the slag is a top slag. To be able to separate the silicon from the slag, it may be necessary to allow the slag to cool somewhat to cause it to set.
The silicon obtained by the method according to the invention has a far higher degree of purification than silicon purified by prior art techniques employ¬ ing slag purification. The boron content, in particu- lar, can be lowered from about 16 ppmw to about 5 ppmw. It has also been found that a considerable purifi¬ cation of the carbon content is achieved. The purifica¬ tion of carbon is especially advantageous if performed in an arc furnace. In an induction furnace, silicon is contaminated by carbon from the graphite lining. How¬ ever, in order to achieve an especially high degree of purification for the remaining impurities, it is neces¬ sary to couple the method according to the invention with a known acid and/or vacuum treatment. The invention will now be described in more detail in the following Examples. Example 1
Equipment: Arc furnace with injection equipment in the form of a graphite lance. hot ladle was filled with about 1700 kg commer¬ cial silicon. The ladle was heated in the arc furnace for about 50 min, after which the temperature was about 1600°C. Then about 1/3 of CaCl2, and after that 1/3 of a mixture of CaO and SiO_ were charged. The procedure was repeated 2 times until all slag-forming agent, in all 1400 kg, had been added. The slag-forming agent consisted of 275 kg CaCl2, 250 kg CaO, and 875 kg SiOp. After the melt had been further heated for about 30 min, the ladle was allowed to cool until the slag had set to such an extent that silicon could be teemed without slag admixture. The silicon charged was analysed both before and after purification. The result is shown in Table 1.
Figure imgf000007_0001
Silicon charged 13 0.26 0.60 0.12 0.01 0.08
Silicon teemed 6 0.37 0.07 0.05 0.01 0.01
It appears from the Table that the boron content is reduced from 13 ppmw in commercial silicon to 6 ppmw in purified silicon.
Example 2
Equipment: Induction furnace with graphite crucible. 300 g silicon are melted and heated to 1500-1600°C. One third of the slag-forming agent which consisted of 50 g CaCl2, 50 g CaO and 175 g Si02, was added. After that, heating to 1500-1600°C was again carried out, and the melt was held for about 30 min. Two fur- ther slag admixtures were carried out in the same man¬ ner. The finished silicon was teemed, allowed to cool and analysed. The result is shown in Table II.
Figure imgf000008_0001
It appears from the Table that the boron content is reduced from 17 to 5 ppmw ("ppmw" means parts per million based on weight).

Claims

1. A method for purifying silicon from boron, by treating crude silicon with molten slag, c h a r a c ¬ t e r i s e d in that silicon is contacted with a slag in which one of the slag-forming components consists of a solid chlorine compound.
2. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that molten silicon is contacted with the slag.
3. A method as claimed in claim 1, c h a r a c - t e r i s e d in that solid chlorine compounds and at least one compound selected from the group consisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals as well as silica are used as slag-forming components.
4. A method as claimed in claim 3, c h a r a c ¬ t e r i s e d in that the slag contains 0.1-50% by weight of solid chlorine compounds, 0-50% by weight of at least one compound selected from the group con¬ sisting of oxides, carbonates and hydroxides of alkali and/or alkaline earth metals, as well as 0-80% by weight of silica.
5. A method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the ratio between the amount of slag and the amount of crude silicon, based on weight, is 0.1-2.
6. A method as claimed in claim 3, c h a r a c ¬ t e r i s e d in that chlorides of alkali and/or alka¬ line earth metals are used as solid chlorine compounds.
7. A method as claimed in claim 6, c h a r a c - t e r i s e d in that CaCl- in an amount of 10-30% by weight of the slag is used as chloride.
8. A method as claimed in claim 3, c h a r a c ¬ t e r i s e d in that CaO is used as oxide-containing compound.
9. A method as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the treatment temperature is from 1410°C, preferably above 1500°C.
PCT/SE1988/000469 1987-09-15 1988-09-12 Method for the purification of silicon WO1989002415A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BR888807699A BR8807699A (en) 1987-09-15 1988-09-12 SILICON PURIFICATION PROCESS
NO901150A NO901150D0 (en) 1987-09-15 1990-03-12 PROCEDURE FOR CLEANING SILICONE.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE8703561A SE460287B (en) 1987-09-15 1987-09-15 PROCEDURE FOR PURIFICATION OF SILICONE FROM BORN
SE8703561-4 1987-09-15

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0699625A1 (en) * 1994-09-01 1996-03-06 Elkem A/S Method for refining silicon
JP2006282499A (en) * 2005-03-07 2006-10-19 Nippon Steel Corp Method for producing high purity silicon
JP2006282498A (en) * 2005-03-07 2006-10-19 Nippon Steel Corp Method for producing high purity silicon
EP1724238A1 (en) * 2004-03-03 2006-11-22 Nippon Steel Corporation Method for removing boron from silicon
CN102583386A (en) * 2012-02-03 2012-07-18 厦门大学 Method for removing impurities such as boron and phosphorus in industrial silicon by slag system doped with chloride
CN103342363A (en) * 2013-06-19 2013-10-09 青岛隆盛晶硅科技有限公司 Slag-forming agent convenient for silicon slag separation in medium smelting of polycrystalline silicon, and application method thereof
WO2014004441A1 (en) * 2012-06-25 2014-01-03 Silicor Materials Inc. Flux composition useful in directional solidification for purifying silicon
CN104276573A (en) * 2013-07-02 2015-01-14 青岛隆盛晶硅科技有限公司 slogging agent for polysilicon medium melting and usage method thereof

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102515168A (en) * 2011-12-12 2012-06-27 昆明理工大学 Method for removing boron impurity in industrial silicon

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2933164A1 (en) * 1979-08-16 1981-02-26 Consortium Elektrochem Ind METHOD FOR CLEANING RAW SILICON

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2933164A1 (en) * 1979-08-16 1981-02-26 Consortium Elektrochem Ind METHOD FOR CLEANING RAW SILICON

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5788945A (en) * 1994-09-01 1998-08-04 Elkem Asa Method for refining of silicon
CN1042821C (en) * 1994-09-01 1999-04-07 埃以凯姆公司 Silicon purifying method
EP0699625A1 (en) * 1994-09-01 1996-03-06 Elkem A/S Method for refining silicon
EP1724238A4 (en) * 2004-03-03 2010-02-17 Nippon Steel Corp Method for removing boron from silicon
US8034151B2 (en) 2004-03-03 2011-10-11 Nippon Steel Corporation Method for removing boron from silicon
EP1724238A1 (en) * 2004-03-03 2006-11-22 Nippon Steel Corporation Method for removing boron from silicon
JP2006282498A (en) * 2005-03-07 2006-10-19 Nippon Steel Corp Method for producing high purity silicon
US7615202B2 (en) * 2005-03-07 2009-11-10 Nippon Steel Materials Co., Ltd. Method for producing high purity silicon
JP2006282499A (en) * 2005-03-07 2006-10-19 Nippon Steel Corp Method for producing high purity silicon
CN102583386A (en) * 2012-02-03 2012-07-18 厦门大学 Method for removing impurities such as boron and phosphorus in industrial silicon by slag system doped with chloride
CN102583386B (en) * 2012-02-03 2014-09-24 厦门大学 Method for removing impurities such as boron and phosphorus in industrial silicon by slag system doped with chloride
WO2014004441A1 (en) * 2012-06-25 2014-01-03 Silicor Materials Inc. Flux composition useful in directional solidification for purifying silicon
CN104619638A (en) * 2012-06-25 2015-05-13 希利柯尔材料股份有限公司 Flux composition useful in directional solidification for purifying silicon
US9512008B2 (en) 2012-06-25 2016-12-06 Silicor Materials, Inc. Flux composition useful in directional solidification for purifying silicon
KR101832575B1 (en) * 2012-06-25 2018-02-26 실리코르 머티리얼즈 인코포레이티드 Flux composition useful in directional solidification for purifying silicon
CN103342363A (en) * 2013-06-19 2013-10-09 青岛隆盛晶硅科技有限公司 Slag-forming agent convenient for silicon slag separation in medium smelting of polycrystalline silicon, and application method thereof
CN104276573A (en) * 2013-07-02 2015-01-14 青岛隆盛晶硅科技有限公司 slogging agent for polysilicon medium melting and usage method thereof

Also Published As

Publication number Publication date
SE8703561L (en) 1989-03-16
EP0408549A1 (en) 1991-01-23
SE8703561D0 (en) 1987-09-15
SE460287B (en) 1989-09-25
BR8807699A (en) 1990-07-24

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