EP0105328A1 - Purification of silicon halides - Google Patents

Purification of silicon halides

Info

Publication number
EP0105328A1
EP0105328A1 EP83901472A EP83901472A EP0105328A1 EP 0105328 A1 EP0105328 A1 EP 0105328A1 EP 83901472 A EP83901472 A EP 83901472A EP 83901472 A EP83901472 A EP 83901472A EP 0105328 A1 EP0105328 A1 EP 0105328A1
Authority
EP
European Patent Office
Prior art keywords
impurities
silicon
trichlorosilane
organosiloxane
boron
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP83901472A
Other languages
German (de)
French (fr)
Other versions
EP0105328A4 (en
Inventor
William David Kray
John Simon Razzano
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
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 General Electric Co filed Critical General Electric Co
Publication of EP0105328A1 publication Critical patent/EP0105328A1/en
Publication of EP0105328A4 publication Critical patent/EP0105328A4/en
Withdrawn legal-status Critical Current

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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
    • C01B33/08—Compounds containing halogen
    • C01B33/107—Halogenated silanes
    • C01B33/10778—Purification

Definitions

  • This invention relates to the preparation of trichlorosilane for the manufacture of electronic grade silicon and, more particularly, to novel methods for removing trace impurities of electrical donor contaminates, especially boron and other Lewis acid or proton donor-type impurities.
  • Silicon of extremely high purity is required for sophisticated electronics uses such as in semiconductors and transistors. It is well known that even trace impurities can seriously impair the performance of silicon-containing electronic components.
  • Elemental silicon for semiconductor use is generally prepared by reduction of silicon halides, such as silicon tetrachloride (SiCl 4 ), trichlorosilane (HSiCl 3 ) and dichlorosilane (H 2 SiCl 2 ), with hydrogen, zinc, sodium or metal hydrides. Silicon may also be derived from thermal decomposition of silane (SiH 4 ), but this latter material is hard to work with because it burns explosively on contact with air.
  • boron One of the most difficult impurities to remove from high purity silicon is boron. Whereas other common impurities such as copper, iron and manganese are comparatively easy to remove by conventional techniques (e.g., zone refining, crystal pulling), boron has physical properties so similar to silicon that separation is accomplished only by repeated trials. Moreover, concentrating purification efforts on the starting materials, e.g., chlorosilanes, is likewise difficult because boron forms corresponding compounds with similar properties.
  • the method of this invention involves contacting the boron halide or other Lewis acid impurity present in a silicon halide solution with a molar excess of an organosiloxane, heating the solution to cause a reaction between the impurities and the siloxane to yield compounds of lower vapor pressure than the silicon halide, and then distilling the pure silicon halide off, leaving the siloxane-bound impurities behind.
  • This method is very effective for removing boron contaminates, especially from solutions of silicon chlorides, such as trichlorosilane.
  • the boron concentration in a solution of trichlorosilane can be reduced by the treatment of the present invention to less than 50 parts per trillion (ppt) .
  • a "Lewis acid” is any substance that will take up an electron pair to form a covalent bond (i.e., "electron-pair acceptor”). This includes the “proton donor” concept of the Lowry-Br ⁇ nsted definition of acids.
  • boron trifluoride (BF 3 ) is a typical Lewis acid, as it contains only six electrons in its outermost electron orbital shell. BF 3 tends to accept a free electron pair to complete its eight-electron orbital.
  • siloxane compounds suitable for the purposes herein are any organosiloxanes which will react with the boron or other impurity present in the silicon halide solution to form impurity-siloxane compounds (e.g., borosiloxane) having a lower vapor pressure than the solution to be purified, such that a pure silicon-containing solution may be distilled from the reaction vessel, leaving the impurity-siloxane compounds behind.
  • impurity-siloxane compounds e.g., borosiloxane
  • siloxanes include alkyl, aryl, halogenated alkyl, halogenated aryl or hydrogen substituted alkyl or aryl cyclotrisiloxanes and cyclotetrasiloxanes such as hexamethylcyclotri siloxane, octamethylcyclotetrasiloxane, polydimethyl siloxane fluids, dimethyl (methyl hydrogensiloxane copolymers and other cyclic siloxane monomers. Cyclotrisiloxanes, alkyl cyclotrisiloxanes, halogenated alkyl cyclotrisiloxanes are preferred; hexamethylcyclotrisiloxane is most preferred.
  • the siloxanes are added to the contaminated silicon halides solution in an amount which will ensure reaction of the siloxanes with the Lewis acid impurities. Best results are obtained if this amount is a large molar excess, for example 5-100 times, based on the concentration of the contaminate. However, any amount of siloxane suitable to effectively bind the impurities present in the solution is contemplated.
  • the mixture is heated to drive the reaction of the siloxanes with the Lewis acid impurities.
  • very high temperatures i.e. , temperatures over 200 oC
  • the reaction may not be sufficient to effectively remove all of the BCl 3 .
  • a reaction temperature range from 25oC to about 200°C is preferred, from about 80oC to about 130°C is most preferred, but higher temperatures are also contemplated so long as the reaction products will not be distilled in the same fraction as the silicon halide, and thereby confound the purification. Best results have been obtained at about 100oC.
  • reaction is allowed to proceed until substantially all of the impurities are bound to siloxane compounds.
  • the time will of course vary according to materials used, temperature used, pressure, etc. Simple experimentation will readily lead to the optimum reaction period for a given purification.
  • the final step in the purification of the present invention is to distill the pure silicon halide from the reaction solution.
  • the decreased volatility of the siloxane-bound impurities compared to the silicon halides makes this final distillation possible.
  • the distillation may be carried out at atmospheric pressures or at higher pressure so long as the temperature of the liquid material does not exceed the decomposition temperature of the borates formed in the process. It is preferred to maintain the temperature of the liquid below about 200oC.
  • TCS trichlorosilane
  • BCl 3 boron trichloride
  • the charge to the distillation vessel was 2000 g. with 99% of the material recovered, the presence of boron was less than 50 parts per trillion in each of the distilled fractions.
  • Example 1 400 parts by weight of 0.018 molar BCl 3 (5000 ppm) in TCS was placed in a reaction vessel with sufficient trimer to make the solution 0.09 molar. The reaction mixture was agitated under pressure and samples distilled periodically for analysis by infrared spectroscopy as in Example 1:

Landscapes

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

Abstract

Ce procédé permet de purifier de manière sélective des halogénures de silicium en éliminant les halogénures de bore et d'autres impuretés de type acide de Lewis. Le traitement des halogénures de silicium aux siloxanes, qui réagissent avec les impuretés, permet de distiller des halogénures de silicium pratiquement décontaminés dans des limites très réduites de détection.This process selectively purifies silicon halides by removing boron halides and other Lewis acid type impurities. The treatment of silicon halides with siloxanes, which react with impurities, makes it possible to distill practically decontaminated silicon halides within very limited detection limits.

Description

PURIFICATION OF SILICON HALIDES
FOR: PURIFICATION OF SILICON HALIDES
This invention relates to the preparation of trichlorosilane for the manufacture of electronic grade silicon and, more particularly, to novel methods for removing trace impurities of electrical donor contaminates, especially boron and other Lewis acid or proton donor-type impurities.
Silicon of extremely high purity is required for sophisticated electronics uses such as in semiconductors and transistors. It is well known that even trace impurities can seriously impair the performance of silicon-containing electronic components.
Elemental silicon for semiconductor use is generally prepared by reduction of silicon halides, such as silicon tetrachloride (SiCl4), trichlorosilane (HSiCl3) and dichlorosilane (H2SiCl2), with hydrogen, zinc, sodium or metal hydrides. Silicon may also be derived from thermal decomposition of silane (SiH4), but this latter material is hard to work with because it burns explosively on contact with air.
One of the most difficult impurities to remove from high purity silicon is boron. Whereas other common impurities such as copper, iron and manganese are comparatively easy to remove by conventional techniques (e.g., zone refining, crystal pulling), boron has physical properties so similar to silicon that separation is accomplished only by repeated trials. Moreover, concentrating purification efforts on the starting materials, e.g., chlorosilanes, is likewise difficult because boron forms corresponding compounds with similar properties.
Various compounds, for example, phenols, tri- phenols, and nitrogen-containing compounds, have been used in the past to complex and bind with impurities in near-pure silicon halide solutions. U.S. Patents 3,403,003 (Morganthaler) ; 3,126,248 (Pohl et al.); and 3,041,141 {Shoemaker et al.), for instance, describe such treatments. The prevailing conventional technique for removing boron contaminates, disclosed in U.S. 4,112,507 (Lang et al.), involves introducing water vapor on silica gel to chlorosilane solutions. However, problems with regeneration of the impurities and corrosion are experienced.
It has now been discovered that boron chlorides and other Lewis acids can be removed almost totally from chlorosilane solutions by the introduction of organo siloxanes. The siloxanes react or complex with the impurit and subsequently react to form thermally stable compounds, i.e., borosiloxanes, which are left behind in a distillation of the chlorosilane.
Accordingly, it is an object of the present invention to provide a novel method for purifying silicon halides.
It is another object of the present invention to provide a method for removing boron halides, Lewis acid a proton donor-type compounds from silicon halide solutions.
It is another object of the present invention to provide a purification method which is irreversible and non-corrosive.
It is another object of the present invention to provide a means of obtaining electronic grade silicon from high purity trichlorosilane.
These and other objects are accomplished herein by a method for purifying silicon halides comprising:
(A) adding to a solution of silicon halide contaminated with Lewis acid impurities a stoichiometric excess, based on the concentration of the impurities, of an organosiloxane;
(B) reacting the impurities in solution with said siloxanes at a temperature of from about 25°C to 200ºC until substantially all the impurities form non-volatile products; and thereafter
(C) removing purified silicon halide by distillation.
DETAILED DESCRIPTION OF THE INVENTION
The method of this invention involves contacting the boron halide or other Lewis acid impurity present in a silicon halide solution with a molar excess of an organosiloxane, heating the solution to cause a reaction between the impurities and the siloxane to yield compounds of lower vapor pressure than the silicon halide, and then distilling the pure silicon halide off, leaving the siloxane-bound impurities behind. This method is very effective for removing boron contaminates, especially from solutions of silicon chlorides, such as trichlorosilane. The boron concentration in a solution of trichlorosilane can be reduced by the treatment of the present invention to less than 50 parts per trillion (ppt) .
For the purposes herein, a "Lewis acid" is any substance that will take up an electron pair to form a covalent bond (i.e., "electron-pair acceptor"). This includes the "proton donor" concept of the Lowry-Brønsted definition of acids. Thus boron trifluoride (BF3) is a typical Lewis acid, as it contains only six electrons in its outermost electron orbital shell. BF3 tends to accept a free electron pair to complete its eight-electron orbital.
The siloxane compounds suitable for the purposes herein are any organosiloxanes which will react with the boron or other impurity present in the silicon halide solution to form impurity-siloxane compounds (e.g., borosiloxane) having a lower vapor pressure than the solution to be purified, such that a pure silicon-containing solution may be distilled from the reaction vessel, leaving the impurity-siloxane compounds behind. These siloxanes include alkyl, aryl, halogenated alkyl, halogenated aryl or hydrogen substituted alkyl or aryl cyclotrisiloxanes and cyclotetrasiloxanes such as hexamethylcyclotri siloxane, octamethylcyclotetrasiloxane, polydimethyl siloxane fluids, dimethyl (methyl hydrogensiloxane copolymers and other cyclic siloxane monomers. Cyclotrisiloxanes, alkyl cyclotrisiloxanes, halogenated alkyl cyclotrisiloxanes are preferred; hexamethylcyclotrisiloxane is most preferred.
The siloxanes are added to the contaminated silicon halides solution in an amount which will ensure reaction of the siloxanes with the Lewis acid impurities. Best results are obtained if this amount is a large molar excess, for example 5-100 times, based on the concentration of the contaminate. However, any amount of siloxane suitable to effectively bind the impurities present in the solution is contemplated.
After the siloxane is mixed into the solution, the mixture is heated to drive the reaction of the siloxanes with the Lewis acid impurities. At very high temperatures, i.e. , temperatures over 200 ºC, there may occur some degradation of the siloxane compound and volatile borates may form. At low temperatures the reaction may not be sufficient to effectively remove all of the BCl3. For these reasons a reaction temperature range from 25ºC to about 200°C is preferred, from about 80ºC to about 130°C is most preferred, but higher temperatures are also contemplated so long as the reaction products will not be distilled in the same fraction as the silicon halide, and thereby confound the purification. Best results have been obtained at about 100ºC. As mentioned before, the reaction is allowed to proceed until substantially all of the impurities are bound to siloxane compounds. The time will of course vary according to materials used, temperature used, pressure, etc. Simple experimentation will readily lead to the optimum reaction period for a given purification.
The final step in the purification of the present invention is to distill the pure silicon halide from the reaction solution. The decreased volatility of the siloxane-bound impurities compared to the silicon halides makes this final distillation possible.
The distillation may be carried out at atmospheric pressures or at higher pressure so long as the temperature of the liquid material does not exceed the decomposition temperature of the borates formed in the process. It is preferred to maintain the temperature of the liquid below about 200ºC.
In order that persons skilled in the art may readily understand the practice of the instant invention, the following examples are provided by way of illustration, and not by way of limitation.
EXAMPLE 1
7 parts by weight hexamethylcyclotrisiloxane (trimer) was admixed with a solution of 150 parts by weight trichlorosilane (TCS) containing 5000 parts per million (ppm) boron trichloride (BCl3) and agitated periodically for 1 hour. A sample of TCS distilled from the reaction mixture content contained no BCl3 or borates as determined by infrared spectroscopy with a limit of detectability of 25 ppm.
EXAMPLE 2
A solution of TCS containing 5 parts per billion (ppb) BCl3 and 25 ppb trimer were mixed at 120°C under 120 psig. A spectroscopic analysis, with a limit of detectability of 25 parts per trillion (ppt) of a sample of distillate indicates that all of the BCl3 was consumed.
EXAMPLE 3
200 ppm of trimer was added to a solution of TCS containing 2 ppm BCl3. The mixture was heated in an oil bath to 130-135ºC at 100 psig for 4 hours. After standing overnight, 4 fractions were distilled and analyzed for boron content by the colorometric method used in Example 2.
The charge to the distillation vessel was 2000 g. with 99% of the material recovered, the presence of boron was less than 50 parts per trillion in each of the distilled fractions.
EXAMPLES 4 and 5
The procedure of Example 3 was repeated twice, with the following results:
EXAMPLE 6
400 parts by weight of 0.018 molar BCl3 (5000 ppm) in TCS was placed in a reaction vessel with sufficient trimer to make the solution 0.09 molar. The reaction mixture was agitated under pressure and samples distilled periodically for analysis by infrared spectroscopy as in Example 1:

Claims

Claims:
1. A method for purifying silicon halides comprising:
(A) adding to a solution of silicon halide contaminated with Lewis acid impurities a stoichiometric excess, based on the concentration of the impurities, of an organosiloxane;
(B) reacting the impurities in solution with said siloxanes at a temperature of from about 25°C to 200ºC until substantially all the impurities form non-volatile products; and thereafter
(C) removing purified silicon halide by distillation.
2. The method of Claim 1 wherein said impurities contain boron.
3. The method of Claim 2 wherein said boron impurities are boron halides.
4. The method of Claim 1 wherein said silicon halides are selected from the group consisting of silicon tetrachloride, trichlorosilane, and dichlorosilane.
5. The method of Claim 4 wherein the silicon halide is trichlorosilane.
6. The method of Claim 1 wherein the organosiloxane is selected from the group consisting of cyclotrisiloxanes, cyclotetrasiloxanes, polydiemthylsiloxane fluids and dimethylmethyl hydrogen siloxane copolymers.
7. The method fo Claim 6 wherein the organosiloxane is a cyclotrisiloxane.
8. The method of Claim 7 wherein the cyclotrisiloxane is selected from the group consisting of cyclotrisiloxane, aryl cyclotrisiloxanes, alkyl cyclotrisiloxane halogenated alkyltrisiloxanes.
9. The method of Claim 8 wherein the -organosiloxane is an alkyl cyclotrisiloxane.
10. The method of Claim 9 wherein the alkyl cyclo trisiloxane is hexamethylcyclotrisiloxane.
11. The method of Claim 6 wherein the organosiloxane is octamethyltetrasiloxane.
12. The method of Claim 1 wherein the organo siloxane is added to a concentration of 5-100 times the molar concentration of the Lewis acid impurities.
13. The method of Claim 1 wherein the silicon halide is trichlorosilane, the Lewis acid impurities are predominantly boron trichloride, the alkyl siloxane is hexamethylcyclotrisiloxane, and the alkyl siloxane is added in a concentration of about 100 times that of the boron trichloride impurity.
14. In the process for producing electronic grade silicon from high purity trichlorosilane, the improvement which comprises purifying the trichlorosilane by the method comprising: (A) adding to a solution of trichlorosilane contaminated with Lewis acid impurities a stoichiometric excess, based on the concentration of the impurities, of an organosiloxane;
(B) reacting the impurities in solution with said siloxanes at a temperature of from about 20ºC to 200°C until substantially all the impurities form non-volatile products; and thereafter (C) removing purified trichlorosilane by distillation.
EP19830901472 1982-03-18 1983-03-17 Purification of silicon halides. Withdrawn EP0105328A4 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US35943782A 1982-03-18 1982-03-18
US359437 1982-03-18

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EP0105328A1 true EP0105328A1 (en) 1984-04-18
EP0105328A4 EP0105328A4 (en) 1984-09-19

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IT (1) IT1163149B (en)
WO (1) WO1983003244A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100826374B1 (en) * 2004-04-13 2008-05-02 다이킨 고교 가부시키가이샤 Chlorotrifluoroethylene Copolymer
EP3002262A1 (en) 2014-10-01 2016-04-06 Heraeus Quarzglas GmbH & Co. KG Method for the manufacture of synthetic quartz glass with polymerizable polyalkylsiloxane

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5660690A (en) * 1996-06-03 1997-08-26 Dow Corning Corporation Method for distilling hexamethylcyclotrisiloxane

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1330442A (en) * 1961-08-04 1963-06-21 Merck & Co Inc Semiconductor body and its manufacturing process

Family Cites Families (5)

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Publication number Priority date Publication date Assignee Title
US3126248A (en) * 1964-03-24 Process for producing purified
US2857249A (en) * 1956-07-03 1958-10-21 Guenter A Wolff Method of purifying silicon tetrachloride
US3403003A (en) * 1966-12-23 1968-09-24 Western Electric Co Method of removing boron from silicon tetrachloride
US3540861A (en) * 1968-02-07 1970-11-17 Union Carbide Corp Purification of silicon compounds
DE2546957C3 (en) * 1975-10-20 1980-10-23 Wacker-Chemitronic Gesellschaft Fuer Elektronik-Grundstoffe Mbh, 8263 Burghausen Process for cleaning halosilanes

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1330442A (en) * 1961-08-04 1963-06-21 Merck & Co Inc Semiconductor body and its manufacturing process

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO8303244A1 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100826374B1 (en) * 2004-04-13 2008-05-02 다이킨 고교 가부시키가이샤 Chlorotrifluoroethylene Copolymer
EP3002262A1 (en) 2014-10-01 2016-04-06 Heraeus Quarzglas GmbH & Co. KG Method for the manufacture of synthetic quartz glass with polymerizable polyalkylsiloxane
US9790120B2 (en) 2014-10-01 2017-10-17 Heraeus Quarzglas Gmbh & Co. Kg Method for the manufacture of synthetic quartz glass

Also Published As

Publication number Publication date
WO1983003244A1 (en) 1983-09-29
IT1163149B (en) 1987-04-08
EP0105328A4 (en) 1984-09-19
IT8320139A0 (en) 1983-03-18

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