CA1145117A - Process for producing polycrystalline silicon - Google Patents
Process for producing polycrystalline siliconInfo
- Publication number
- CA1145117A CA1145117A CA000327660A CA327660A CA1145117A CA 1145117 A CA1145117 A CA 1145117A CA 000327660 A CA000327660 A CA 000327660A CA 327660 A CA327660 A CA 327660A CA 1145117 A CA1145117 A CA 1145117A
- Authority
- CA
- Canada
- Prior art keywords
- silicon
- reactor
- temperature
- product
- tribromosilane
- 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.)
- Expired
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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
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Silicon Compounds (AREA)
Abstract
A B S T R A C T
An economical, low temperature, closed loop, thermal decomposition process is provided for producing a controllable mixture of heterogeneously and homogeneously nucleated ultrahigh purity polycrystalline silicon suitable for use in the manufacture of semiconductor devices and photovoltaic solar cells. The pro-cess manipulates the equilibrium expressed by the chemical reaction:
Si + 2H2 + 3SiBr4
An economical, low temperature, closed loop, thermal decomposition process is provided for producing a controllable mixture of heterogeneously and homogeneously nucleated ultrahigh purity polycrystalline silicon suitable for use in the manufacture of semiconductor devices and photovoltaic solar cells. The pro-cess manipulates the equilibrium expressed by the chemical reaction:
Si + 2H2 + 3SiBr4
Description
~1~511~7 ~1 PROCESS FOR PRODUCING POLYCRYSTALLINE SILICON .
~2~ :BACKGROUND OF THE INVENTION
.
3 United States Patent 4,084,024 which issued April 11, 197~ in the name of Joseph C. Schumacher, and which is assigned to the present assignee, discloses and claims a process for the 6 ~ production of semiconductor grade silicon using hydrogen reduction ~7~: ::at:relatively high temperatures, for example, within a temperature : .
~-:8 ~ range of from 900C - 1200C. The process of the present invention, :~9; on the other hand, in~olves a process for producing semiconductor grade sllicon involving the use of thermal decomposition which is L~l carried:out at a lower and more economucal temperature range of, 12 for example, 500C - 900DC.
.. ' ~ `
.
~ 1~4S117 1 ¦ As pointed out in the patent, recent developments in the
~2~ :BACKGROUND OF THE INVENTION
.
3 United States Patent 4,084,024 which issued April 11, 197~ in the name of Joseph C. Schumacher, and which is assigned to the present assignee, discloses and claims a process for the 6 ~ production of semiconductor grade silicon using hydrogen reduction ~7~: ::at:relatively high temperatures, for example, within a temperature : .
~-:8 ~ range of from 900C - 1200C. The process of the present invention, :~9; on the other hand, in~olves a process for producing semiconductor grade sllicon involving the use of thermal decomposition which is L~l carried:out at a lower and more economucal temperature range of, 12 for example, 500C - 900DC.
.. ' ~ `
.
~ 1~4S117 1 ¦ As pointed out in the patent, recent developments in the
2 ¦ semiconductor industry have created a growing demand for a low cost
3 ¦ single crystal silicon of extremely high purity, which is known as
4 ¦ semiconductor grade silicon, and which is used in the manufacture
5 ¦ of semiconductor devices and silicon voltaic solar cells. For
6 ¦ that reason, a multitude of prior art processes have been conceived
7 ¦ for the production of semiconductor grade silicon, including the
8 ¦ process covered by the patent. The prior art processes can be
9 ¦ classi~ied into the following six basic approaches:
11¦ 1. The Siemens process described in GDR Patents 1,066,564;
12¦ 1,102,117; 1,233,815 and British Patent 904,239 by which essentially 13¦ all current semiconductor grade polycrystalline silicon is produced, 14¦ is expressed by the following chemical reaction.
16 o Si(MG) + HCl t lYst~ SiCL4 + SiHC13 + other byproducts 18 o SiHC13 + H2 ~ Si + SiC14 + HCl + explosive pvlymer 21 This is a high temperature batch process providing 22 heterogeneously nucleated silicon growth on heated Si filaments 23 and large volumes of SiC14 and exPlosive polymeric byproducts which Z4 must be disposed of. The process is as a result of these byproducts, not a closed-loop process. In addition a 20/1 excess of H2 over 26 stoichiometry is required.
2~
29 2. Silicon tetrachloride - hydrogen reduction is utilized 32 some cases because of the availability of byproduct SiC14 from .
~ 5117 1 the Siemens process. An alternative SiC14 production reaction is 2 included here since it may be used as a source.
4 Si + 2C12 ~ SiC14 6 SiC14 + ~H2 > Si + 4HCl + polymers 8 This again is a high temperature, non-closed-loop, batch 9 process providing heterogeneously nucleated growth on a heated substrate and requires a large H2 excess.
1 . I ~ ~
13 3. The DuPont process as described in U. S. Patents 14 ¦ 3,012,862 and 4,084,024 where in SiX4 or SiHX3 (where X = Cl,Br,I) is reduced in a fluid or moving bed by H2,Zn, or Cd. The reaction 16 chemistry is as follows:
18 I. Feed preparation 19 IMG)Si + 3HX ~ SiHX3 + SiX4 + H2 etc.
with SiX4 here a byproduct 22 or (MG)5i + 2X2 > SiX4 II. Ultrapure silicon production by 27 SiHX + H 1100-1200C~ Si + HX + SiX
28 + polymers for X = Cl 29 or ~145117 l 4 2 ~ Si + HX + polymers 2 or 3 SiHX3 + M 90~ 1 ~ Si-+ H2 + MX2 -(M = Zn,Cd) 4 or SiX4 + M > Si + MX2 (M = Zn,Cd~
8 These are moderately high temperature, non-closed loop pro-9 cesses with the byproducts varying with the particular process chemistry, and which require large hydrogen excesses where it is ll used.
14 4. The Iodide process described in U. S. Patent 3,020,129 expressed as follows:
l Si + 2I2 ~ SiI4 17 and thermal decomposition to produce Si 1 SiI4 ~ C ~Si + 2I2 19 : 1l This is a moderate-temperature closed-loop batch process 2 in which:polycrystalline or single crystal silicon is grown on a 2 seed particle or heated filament.
5. The Union carbide process expressed as follows:
2 Tricholorosilane preparation 2 Si + 2H2 + 3SiC14 S00 C ' 45iHCl3 3l 11 _4_ 11~5117 1 Ion exchange redistribution to silane according to 2C12 Amberlite~ SiH3Cl + SiHC13 7 o4SiH3cl berl;Ce> 3SiH4 + SiC14 9 with appropriate byproduct recycle followed by silane thermal decomr lO position.
lZ Si~ 500-900C~ Si + 2H
13 .
14 This is a low temperature, closed-loop process involving an ion exchange intermediate redistribution and produces homo-16 geneously nucleated product.
17 .
~19 6. The thermal decomposition of trichlorosilane according 20 to 21 .
22 4SiBC1 800-1000C~ Si + 2~ + 3SiCl a3 :24 is described in U. S. Patents 2,943,918 and 3,nl2,861. Presumably as the trichlorosilane is prepared according to .
26 .
~27 Si + HCl ~ SiHC13 + SiC14 + other products ¦
~as SO : ~
32 ~ ' . ~, .
_5_ 51~'~
so that a non-closed process would result. Only batch type opera-tion is proposed to promote heterogeneous nucleation and homo-geneous nucleation is avoided and thought harmful.
Many other techniques and slight modifications of the tech-niques presented are contained within the prior art, however, nonewould appear to have a material bearing on the present invention.
The invention in its broader aspects pertains to a process for producing high purity silicon by the thermal decomposition of halosilane. The improvement comprises passing tribromosilane sub-
11¦ 1. The Siemens process described in GDR Patents 1,066,564;
12¦ 1,102,117; 1,233,815 and British Patent 904,239 by which essentially 13¦ all current semiconductor grade polycrystalline silicon is produced, 14¦ is expressed by the following chemical reaction.
16 o Si(MG) + HCl t lYst~ SiCL4 + SiHC13 + other byproducts 18 o SiHC13 + H2 ~ Si + SiC14 + HCl + explosive pvlymer 21 This is a high temperature batch process providing 22 heterogeneously nucleated silicon growth on heated Si filaments 23 and large volumes of SiC14 and exPlosive polymeric byproducts which Z4 must be disposed of. The process is as a result of these byproducts, not a closed-loop process. In addition a 20/1 excess of H2 over 26 stoichiometry is required.
2~
29 2. Silicon tetrachloride - hydrogen reduction is utilized 32 some cases because of the availability of byproduct SiC14 from .
~ 5117 1 the Siemens process. An alternative SiC14 production reaction is 2 included here since it may be used as a source.
4 Si + 2C12 ~ SiC14 6 SiC14 + ~H2 > Si + 4HCl + polymers 8 This again is a high temperature, non-closed-loop, batch 9 process providing heterogeneously nucleated growth on a heated substrate and requires a large H2 excess.
1 . I ~ ~
13 3. The DuPont process as described in U. S. Patents 14 ¦ 3,012,862 and 4,084,024 where in SiX4 or SiHX3 (where X = Cl,Br,I) is reduced in a fluid or moving bed by H2,Zn, or Cd. The reaction 16 chemistry is as follows:
18 I. Feed preparation 19 IMG)Si + 3HX ~ SiHX3 + SiX4 + H2 etc.
with SiX4 here a byproduct 22 or (MG)5i + 2X2 > SiX4 II. Ultrapure silicon production by 27 SiHX + H 1100-1200C~ Si + HX + SiX
28 + polymers for X = Cl 29 or ~145117 l 4 2 ~ Si + HX + polymers 2 or 3 SiHX3 + M 90~ 1 ~ Si-+ H2 + MX2 -(M = Zn,Cd) 4 or SiX4 + M > Si + MX2 (M = Zn,Cd~
8 These are moderately high temperature, non-closed loop pro-9 cesses with the byproducts varying with the particular process chemistry, and which require large hydrogen excesses where it is ll used.
14 4. The Iodide process described in U. S. Patent 3,020,129 expressed as follows:
l Si + 2I2 ~ SiI4 17 and thermal decomposition to produce Si 1 SiI4 ~ C ~Si + 2I2 19 : 1l This is a moderate-temperature closed-loop batch process 2 in which:polycrystalline or single crystal silicon is grown on a 2 seed particle or heated filament.
5. The Union carbide process expressed as follows:
2 Tricholorosilane preparation 2 Si + 2H2 + 3SiC14 S00 C ' 45iHCl3 3l 11 _4_ 11~5117 1 Ion exchange redistribution to silane according to 2C12 Amberlite~ SiH3Cl + SiHC13 7 o4SiH3cl berl;Ce> 3SiH4 + SiC14 9 with appropriate byproduct recycle followed by silane thermal decomr lO position.
lZ Si~ 500-900C~ Si + 2H
13 .
14 This is a low temperature, closed-loop process involving an ion exchange intermediate redistribution and produces homo-16 geneously nucleated product.
17 .
~19 6. The thermal decomposition of trichlorosilane according 20 to 21 .
22 4SiBC1 800-1000C~ Si + 2~ + 3SiCl a3 :24 is described in U. S. Patents 2,943,918 and 3,nl2,861. Presumably as the trichlorosilane is prepared according to .
26 .
~27 Si + HCl ~ SiHC13 + SiC14 + other products ¦
~as SO : ~
32 ~ ' . ~, .
_5_ 51~'~
so that a non-closed process would result. Only batch type opera-tion is proposed to promote heterogeneous nucleation and homo-geneous nucleation is avoided and thought harmful.
Many other techniques and slight modifications of the tech-niques presented are contained within the prior art, however, nonewould appear to have a material bearing on the present invention.
The invention in its broader aspects pertains to a process for producing high purity silicon by the thermal decomposition of halosilane. The improvement comprises passing tribromosilane sub-
10 stantially undiluted through a bed of high purity silicon substrateparticles in a walled product reactor at a reaction temperature of from about 600 to about 800 degrees C., a pressure of at least about atmospheric pressure and while the te~perature of the walls of the product reactor is above the reaction temperature. Thus 15 thermal decomposition of the tribromosilane is effected to de-posit high purity polycrystalline silicon on the substrate par-ticles and to produce silicon tetrabromide and hydrogen as reaction products without the production of silicon polymers as an ex-plosive byproduct and amophous silicon as a clogging byproduct, 20 the reactor product wall temperature being such as to prevent accumulation of product reactor wall scale.
More particularly the process may include the steps of (~pro-viding tribromosilane by reacting silicon, silicon tetrabromide and hydrogen in a synthesis reactor at a temperature o~ from about 25 450 to about 650 degreesC.~ O separating tribromosilane produced in step (a) from reagents and other reaction products of step (a);
(c) passing the separated tribromosilane from step (b) substantially undiluted through a bed of high purity silicon substrate particles in a manner noted above to effect thermal decomposition of the 30 tribromosilane and produce the silicon tetrabromide and hydrogen reaction byproducts; (d) feeding these byproducts into the synthesis step (a~.
An important feature of the process of the invention is , ~Sl~'7 that it is a continuous process unlike the prior art batch process 1, 2, 4 and 6 described briefly above. As is well known, the con-tinuous process represents an improvement over the batch processes in the reduction of capital costs and operating expenses per unit of product.
Another important feature of the process of the present in~
vention is that it is a closed-loop low temperature process; where-as the prior art processes 1, 2, 3 and 6, supra, are high tempera-ture, open-loop processes. The prior art processes represent high-10 er operating expenses due to their excessive energy requirementsand the need for the disposal of corrosive and hazardous byproducts.
Another feature of the process of the invention is that it utilizes a direct high yield thermal decomposition of trihalosi-lane in contrast to the low yield thermal decomposition process 15 of U. S. Patents 2,943,918 and 3,012,861, rather than going through the ion exchange redistribution of prior art process 5 in order to obtain a material suitable for thermal decomposition.
The inherent simplicity of the process of the present invention results in a reduction in complexity and operating costs and an 20 improvement in yield capabilities.
Another important feature of the process of the invention is the avoidance of wall build-up in the thermal decomposition reac-tion by maintaining a critical temperature differential between the bed and the surrounding walls.
BRIEF DESCRIPTION OF T~E DRAWING
FIGURE 1 is a schematic representation of one embodiment of the process of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
In the first process step, in accordance with-the invention, 30 metallurgical grade silicon metal of approximately 95% or greater purity is reacted with hydrogen (H2) and the appropriate silicon tetrabromide (SiBr4) in a crude silicon converter 10 to produce tribromosilane, and in which the reaction:
Si + 3SiBr4 + 2H2 --~4Hsisr3 is carried out. The converter may be a first stage fluid bed reac-tor maintained within a temperature range of substantially 400~C -650C, and at atmospheric or greater pressure. The converter may be of ~he type described, for example, in U.5. patent 2,993,762.
The metallurgical grade silicon may be generated locally in an electrothermic silicon generator of known construction, as described in U. S. Patent 4,084,024, or it may be obtained from usual commercial sources. The metallurgical grade silicon is pre-ferably in the particle size range of 50-500 microns to provide good fluidiza~ion characteristics. Fluidization is provided by hydrogen gas containing tetrabroMide vapor ~hich is introduced into the reactor through an inlet vaporizer 12. Conversion efficiencies of 3Q~ or greater of stoichiometric are achieved in the reactor.
A mixture of tribromosllane (SiHBr3) and unreacted hydrogen (H2) and tetrabromosilane is carried from the top of the reactor 10 ln vapor phase to a condenser 14. Impurity metaL halides are removed from'the bottom of'reactor 10.
The hydrogen and tribromosllane are separated out in a ~20 separator 16, with the hydrogen being returned to the reac-tor,10. The tribromosilane is introduced to a refiner 18 in which it is purified in accordance with the second step of the process.
During the second step unreacted silicon tetr~romide is recovered ~ -8-and returned to the feed system for the reactor 10 through a surge drum 20.
It is important to recognize that the conversion reaction in reactor 10 in accordance with the first step of the process of the invention occurs in a non-equilibrium manner. That is to say, the reaction at 400-650C in the reactor of ., Si + 2H2 + 3SiBr4~ 4SiHBr3 has a positive free energy of 5-20 Rcal per mole and an equilibrium constant less than unity since a ~ = -RTLnKp. As a result, the reaction products must be continuously removed from the reactor.
The production of tribromosilane (SiHBr3) thereby occurs as a result of the operation of the law of mass action under non-equilibrium conditions.
The sécond step of the process involves the purification of the tribromosilane in a refiner l8 by the distillation of-the tribr~omosilane prior to the fur-theI processillc~ ~here~3L ln~o u1~.rn-high purity polycrystalline silicon. Refiner 18 may be a simple, multi-plate distillation column, and it is utilized to separate the feed triPromosilane into a mixture of less than 5% tetrabromo-silane in tribromosilane of metallic and organic impurity content less than 100 parts per billion total; and a mixture of tri~rom silane and tetrabromosilane which has significantly greater than 25 ~ ~lOO~parts per billion metallic and org~ic impurities, as bottoms.
The~bottoms are returned to the first sta~e reactor 10 through the , .;~ 7 ~,``, ~ .
,.~, g ~1~5117 surge drum 20, as explained above. The overhead is fed to a reactor 28 through a condenser 22 and separator 24, and through an inlet vaporizer 26, so that the third step of the process may be carried out. As in the previous stage, the hydrogen from separator 24 is recycled to the feed for the first stage reactor 10. Refiner 18 may be of the type described in detail in Adcock et al U. S. Patent 3,120,128.
The third step of the process of the invention effectuates the thermal decomposition of trl~romosilane in a reactor 28 within a temperature range of the order of 600 - 800C, and at atmospheric or reduced pressure. The thermal decomposition is in accordance with the reaction 4HSiBr3- /~Si + 3SiBr4 + 2H2.
The product, ultrapure semiconductor grade silicon is prDduced in reactor 28 along with the byproducts hydrogen and tetra-bromo~ilane. The byproducts are recovered and separated by a con-denser 30 and separator 32, and they are recycled as fecd fol ~he first stage reactor 10, as illustrated, to achieve a closed-loop process.
~20 The recycled hydrogen is purified in an activated carbon filter 34 of known construction, and is compressed by a compressor 36. The purified and compressed hydrogen is then passed t~ a mix-ing euductor 38, in which it is mixed with the silicon tetra~romide A
~45~17 from surge drum 20 and fed to the first stage reactor 10. Make-up hydrogen may also be added, as indicated.
.
Reactor 28 may be a moving bed reactor of the type described in detail in U. S. Patent 4,084,024; or it may be a fluid bed reactor of the type described in U. S. Patents 3,012,861;
3,012,862 or 3,963,838.
An important feature of the process of the present inven-tion is the production of ultra-pure semiconductor grade silicon in reactor 28 at a relatively low temperature lying, for example, within a range of essentially 500 - 800C, without the introduc-tion of hydrogen into the reactor; as compared with the high tem-perature (900C - 1500C) hydrogen reduction in the reactor as described in U. S. Patent 4,084,024. The process of the present invention is predicated upon the premise that the chemical reaction 4HSiBr3 ~ Si. + 3SiBr4 + 2H2 occurs in a temperature ran~e of the order of 600O-80aoC producing a high yield (80~ - 100%) of purified semiconductor grade silicon deposited on a substrate consisting of-fine particles of the puri-20 fied silicon.
.
:: :
Above 900C, for example, the mechanism of reactor 28 changes and the yield of silicon falls tc- a lo~ ~alue, of the orde~-of 10%, as described, for example, in U. S. Patent 3,012,8~1.
.
More particularly the process may include the steps of (~pro-viding tribromosilane by reacting silicon, silicon tetrabromide and hydrogen in a synthesis reactor at a temperature o~ from about 25 450 to about 650 degreesC.~ O separating tribromosilane produced in step (a) from reagents and other reaction products of step (a);
(c) passing the separated tribromosilane from step (b) substantially undiluted through a bed of high purity silicon substrate particles in a manner noted above to effect thermal decomposition of the 30 tribromosilane and produce the silicon tetrabromide and hydrogen reaction byproducts; (d) feeding these byproducts into the synthesis step (a~.
An important feature of the process of the invention is , ~Sl~'7 that it is a continuous process unlike the prior art batch process 1, 2, 4 and 6 described briefly above. As is well known, the con-tinuous process represents an improvement over the batch processes in the reduction of capital costs and operating expenses per unit of product.
Another important feature of the process of the present in~
vention is that it is a closed-loop low temperature process; where-as the prior art processes 1, 2, 3 and 6, supra, are high tempera-ture, open-loop processes. The prior art processes represent high-10 er operating expenses due to their excessive energy requirementsand the need for the disposal of corrosive and hazardous byproducts.
Another feature of the process of the invention is that it utilizes a direct high yield thermal decomposition of trihalosi-lane in contrast to the low yield thermal decomposition process 15 of U. S. Patents 2,943,918 and 3,012,861, rather than going through the ion exchange redistribution of prior art process 5 in order to obtain a material suitable for thermal decomposition.
The inherent simplicity of the process of the present invention results in a reduction in complexity and operating costs and an 20 improvement in yield capabilities.
Another important feature of the process of the invention is the avoidance of wall build-up in the thermal decomposition reac-tion by maintaining a critical temperature differential between the bed and the surrounding walls.
BRIEF DESCRIPTION OF T~E DRAWING
FIGURE 1 is a schematic representation of one embodiment of the process of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
In the first process step, in accordance with-the invention, 30 metallurgical grade silicon metal of approximately 95% or greater purity is reacted with hydrogen (H2) and the appropriate silicon tetrabromide (SiBr4) in a crude silicon converter 10 to produce tribromosilane, and in which the reaction:
Si + 3SiBr4 + 2H2 --~4Hsisr3 is carried out. The converter may be a first stage fluid bed reac-tor maintained within a temperature range of substantially 400~C -650C, and at atmospheric or greater pressure. The converter may be of ~he type described, for example, in U.5. patent 2,993,762.
The metallurgical grade silicon may be generated locally in an electrothermic silicon generator of known construction, as described in U. S. Patent 4,084,024, or it may be obtained from usual commercial sources. The metallurgical grade silicon is pre-ferably in the particle size range of 50-500 microns to provide good fluidiza~ion characteristics. Fluidization is provided by hydrogen gas containing tetrabroMide vapor ~hich is introduced into the reactor through an inlet vaporizer 12. Conversion efficiencies of 3Q~ or greater of stoichiometric are achieved in the reactor.
A mixture of tribromosllane (SiHBr3) and unreacted hydrogen (H2) and tetrabromosilane is carried from the top of the reactor 10 ln vapor phase to a condenser 14. Impurity metaL halides are removed from'the bottom of'reactor 10.
The hydrogen and tribromosllane are separated out in a ~20 separator 16, with the hydrogen being returned to the reac-tor,10. The tribromosilane is introduced to a refiner 18 in which it is purified in accordance with the second step of the process.
During the second step unreacted silicon tetr~romide is recovered ~ -8-and returned to the feed system for the reactor 10 through a surge drum 20.
It is important to recognize that the conversion reaction in reactor 10 in accordance with the first step of the process of the invention occurs in a non-equilibrium manner. That is to say, the reaction at 400-650C in the reactor of ., Si + 2H2 + 3SiBr4~ 4SiHBr3 has a positive free energy of 5-20 Rcal per mole and an equilibrium constant less than unity since a ~ = -RTLnKp. As a result, the reaction products must be continuously removed from the reactor.
The production of tribromosilane (SiHBr3) thereby occurs as a result of the operation of the law of mass action under non-equilibrium conditions.
The sécond step of the process involves the purification of the tribromosilane in a refiner l8 by the distillation of-the tribr~omosilane prior to the fur-theI processillc~ ~here~3L ln~o u1~.rn-high purity polycrystalline silicon. Refiner 18 may be a simple, multi-plate distillation column, and it is utilized to separate the feed triPromosilane into a mixture of less than 5% tetrabromo-silane in tribromosilane of metallic and organic impurity content less than 100 parts per billion total; and a mixture of tri~rom silane and tetrabromosilane which has significantly greater than 25 ~ ~lOO~parts per billion metallic and org~ic impurities, as bottoms.
The~bottoms are returned to the first sta~e reactor 10 through the , .;~ 7 ~,``, ~ .
,.~, g ~1~5117 surge drum 20, as explained above. The overhead is fed to a reactor 28 through a condenser 22 and separator 24, and through an inlet vaporizer 26, so that the third step of the process may be carried out. As in the previous stage, the hydrogen from separator 24 is recycled to the feed for the first stage reactor 10. Refiner 18 may be of the type described in detail in Adcock et al U. S. Patent 3,120,128.
The third step of the process of the invention effectuates the thermal decomposition of trl~romosilane in a reactor 28 within a temperature range of the order of 600 - 800C, and at atmospheric or reduced pressure. The thermal decomposition is in accordance with the reaction 4HSiBr3- /~Si + 3SiBr4 + 2H2.
The product, ultrapure semiconductor grade silicon is prDduced in reactor 28 along with the byproducts hydrogen and tetra-bromo~ilane. The byproducts are recovered and separated by a con-denser 30 and separator 32, and they are recycled as fecd fol ~he first stage reactor 10, as illustrated, to achieve a closed-loop process.
~20 The recycled hydrogen is purified in an activated carbon filter 34 of known construction, and is compressed by a compressor 36. The purified and compressed hydrogen is then passed t~ a mix-ing euductor 38, in which it is mixed with the silicon tetra~romide A
~45~17 from surge drum 20 and fed to the first stage reactor 10. Make-up hydrogen may also be added, as indicated.
.
Reactor 28 may be a moving bed reactor of the type described in detail in U. S. Patent 4,084,024; or it may be a fluid bed reactor of the type described in U. S. Patents 3,012,861;
3,012,862 or 3,963,838.
An important feature of the process of the present inven-tion is the production of ultra-pure semiconductor grade silicon in reactor 28 at a relatively low temperature lying, for example, within a range of essentially 500 - 800C, without the introduc-tion of hydrogen into the reactor; as compared with the high tem-perature (900C - 1500C) hydrogen reduction in the reactor as described in U. S. Patent 4,084,024. The process of the present invention is predicated upon the premise that the chemical reaction 4HSiBr3 ~ Si. + 3SiBr4 + 2H2 occurs in a temperature ran~e of the order of 600O-80aoC producing a high yield (80~ - 100%) of purified semiconductor grade silicon deposited on a substrate consisting of-fine particles of the puri-20 fied silicon.
.
:: :
Above 900C, for example, the mechanism of reactor 28 changes and the yield of silicon falls tc- a lo~ ~alue, of the orde~-of 10%, as described, for example, in U. S. Patent 3,012,8~1.
.
-11-11~5117 Hydrogen must be added in the high temperature range above 900C, as described in U. S. Patent 4,084,024, in order to produce high quality silicon in accordance with the reaction ~SiBr3 + H2 ~ Si + 3HBr Another important feature of the process of the invention is its "closed loop" aspect, which makes the process economically feasible. Specifically, there are essentially no byproducts pro-duced by the process which are not recycled back for re-use, and the only material actually "consumed" in the process is impure sili-con, which is converted into ultra-pure semiconductor grade silicon.
Accordingly, in the process of the invention, product silicon from tribromo~ilane thermal decomposition is produced as a mi~ture of homogeneously nucleated fine powder and hetero-geneously nucleated silicon growth upon the fluid or moving bed substrate particles in reactor 28. The relative proportion of homogeneous to heterogeneous nucleation is controlled by several factors including, but not limited to, tl) feed stock (tribromo-silane or trichlorosilane); (2) decomposition temperature and pres-` sure; (3) bed (substrate) particle size distribution and surface ~20 pre-treatment; (4) bed velocity and vapor-particle relative velo-city; and t5) bed depth and residence time.
: ::
': :
,~
Accordingly, in the process of the invention, product silicon from tribromo~ilane thermal decomposition is produced as a mi~ture of homogeneously nucleated fine powder and hetero-geneously nucleated silicon growth upon the fluid or moving bed substrate particles in reactor 28. The relative proportion of homogeneous to heterogeneous nucleation is controlled by several factors including, but not limited to, tl) feed stock (tribromo-silane or trichlorosilane); (2) decomposition temperature and pres-` sure; (3) bed (substrate) particle size distribution and surface ~20 pre-treatment; (4) bed velocity and vapor-particle relative velo-city; and t5) bed depth and residence time.
: ::
': :
,~
-12-1~45~1';J
It is important to ccntrol the ratio of homogeneous to heterogeneous nucleation to (1) achieve a self-perpetuating bed whexein growth substrate particles are grown in situ rather than being prepared from the product in a separate grinding operation and (2) to maximize conversion efficiency and rate. Conversion efficiencies of greater than 80-90~ of theoretical are routinely achieved.
In the practice of the process of the invention, it is advantageous to hold wall temperatures in the fluid or moving bed reactor 28 at greater than 900C while maintaining bed temperature between 700C and 800C. Wall deposits and reactor plugging are thereby avoided. In most fluid or moving bed reactors, reaction heat for endothermic chemical reactions is obtained by heating the reactor walls by gas firing, resistance heating, induction heatin~
or by various other means. However, reaction rate and extent are generally directly proportional to temperature so that considerabl reaction and deposition takes place on the walls as described in U. S. Patent 3,963,838. These deposits generally occur at the highest temperature portion of the reactor. Wall deposits, thus formed, in time build up and causa, not only time-dependent heat transfer characteristics, but also reduced heat transfer and even-- tual reactor plugging. It has been found that silicon deposition from the thermal decomposition of tribro~osilane ceases at a tem-perature of 900C-1000C. Thus, wall deposition in the process of 25 ~ the present invention is avolded by holding wall temperatures in range of 900C-1000C, while maintaining bed temperatures in a range e~tending from 700 to 850C to establish ma~imum silicon deposition rate and yield.
~ ~ 5117 1 ~ A specific example of the conversion of tetrabromosilane 2 ¦ to tribromosilane in the first stage reactor 10 is as follows:
4 ¦ A combined gaseous stream of hydrogen and tetrabromo-5 ¦ silane were introduced into reactor 10 which contained a heated bed 6 ¦ of silicon particles. The gaseous stream had a composition of 7 ¦ 2.23 moles of hydrogen per mole of tetrabromosilane. The silicon 8 ¦ bed had a cross-sectional area of 4.54 square centimeters and a 9 ¦ length of 40 centimeters. The bed temperature was maintained at 10 ¦ 650C, and the average residence time of the gaseous stream was 11 ¦ 5.1 seconds. The silicon particles introduced into the reactor 10 12 ¦ were metallurgical grade. Condensation of the exit stream from the
It is important to ccntrol the ratio of homogeneous to heterogeneous nucleation to (1) achieve a self-perpetuating bed whexein growth substrate particles are grown in situ rather than being prepared from the product in a separate grinding operation and (2) to maximize conversion efficiency and rate. Conversion efficiencies of greater than 80-90~ of theoretical are routinely achieved.
In the practice of the process of the invention, it is advantageous to hold wall temperatures in the fluid or moving bed reactor 28 at greater than 900C while maintaining bed temperature between 700C and 800C. Wall deposits and reactor plugging are thereby avoided. In most fluid or moving bed reactors, reaction heat for endothermic chemical reactions is obtained by heating the reactor walls by gas firing, resistance heating, induction heatin~
or by various other means. However, reaction rate and extent are generally directly proportional to temperature so that considerabl reaction and deposition takes place on the walls as described in U. S. Patent 3,963,838. These deposits generally occur at the highest temperature portion of the reactor. Wall deposits, thus formed, in time build up and causa, not only time-dependent heat transfer characteristics, but also reduced heat transfer and even-- tual reactor plugging. It has been found that silicon deposition from the thermal decomposition of tribro~osilane ceases at a tem-perature of 900C-1000C. Thus, wall deposition in the process of 25 ~ the present invention is avolded by holding wall temperatures in range of 900C-1000C, while maintaining bed temperatures in a range e~tending from 700 to 850C to establish ma~imum silicon deposition rate and yield.
~ ~ 5117 1 ~ A specific example of the conversion of tetrabromosilane 2 ¦ to tribromosilane in the first stage reactor 10 is as follows:
4 ¦ A combined gaseous stream of hydrogen and tetrabromo-5 ¦ silane were introduced into reactor 10 which contained a heated bed 6 ¦ of silicon particles. The gaseous stream had a composition of 7 ¦ 2.23 moles of hydrogen per mole of tetrabromosilane. The silicon 8 ¦ bed had a cross-sectional area of 4.54 square centimeters and a 9 ¦ length of 40 centimeters. The bed temperature was maintained at 10 ¦ 650C, and the average residence time of the gaseous stream was 11 ¦ 5.1 seconds. The silicon particles introduced into the reactor 10 12 ¦ were metallurgical grade. Condensation of the exit stream from the
13¦ reactor in condenser 14, followed by subsequent distillation of the
14¦ condensate in the purification distillation column 18 indicated a
15¦ 36% conversion of the tetrabromosilane into tribromosilane. Con-
16¦ version is defined as the moles of tribromosilane obtained from the
17¦ reaction divided by the initial number of moles of tetrabromosilane
18¦ introduced into the reactor.
21¦ Specific example of the decomposition of tribromosilane 221 to silicon in reactor 28.
241 A gaseous stream of argon and tribromosilane having a 251 composition of 7.7 moles of argon per mole of tribromosilane was 26¦ introduced into a fluidized bed reactor. Although not essential 271 to the practice of the invention, the argon served as both the 28¦ tribromosilane carrier and fluidizing gas for the bed of silicon 291 particles within the reactor. The bed of silicon particles con-31 sist d of 50 mesh particles and ha~ a total mass at the start of ~ 14-1~5117 the reaction of 258 gra~s. The bed was maintained at a temperature of 786C~800C during the reaction.
A total of 1.57 moles of tribromosilane was introduced into the reactor during the run. Removal of the silicon particles at the end of the run showed that the bed had a mass of 268.1 grams or a weight gain of lO.l grams or a yield of 91%, based on the decomposition reaction 4HSiBr3 > Si + 3SiBr4 t 2H2 The invention provides, therefore, a low-temperature, closed-loop continuous process for the economical production of high purity semiconductor grade silicon. The process of the inven-tion, as described, utilizes the direct thermal decomposition of trihalosilane at relatively low temperatures (below 900C) to pro-duce ultra-pure silicon. The process also avoids silicon wall ~15 build-up in the reactor by maintaining a temperature differential ; ~between the bed and the surrounding wall such that the lowest temperature of the wall is above the threshold temperature at which silicon is deposited thereon.
~, .
It will be appreclated that although a particular embodi-ment of the invention has been shown and described, modifications may be made. It is intended in the claims to cover the modifications which come within the true spirit and scope of the invention.
.
'
21¦ Specific example of the decomposition of tribromosilane 221 to silicon in reactor 28.
241 A gaseous stream of argon and tribromosilane having a 251 composition of 7.7 moles of argon per mole of tribromosilane was 26¦ introduced into a fluidized bed reactor. Although not essential 271 to the practice of the invention, the argon served as both the 28¦ tribromosilane carrier and fluidizing gas for the bed of silicon 291 particles within the reactor. The bed of silicon particles con-31 sist d of 50 mesh particles and ha~ a total mass at the start of ~ 14-1~5117 the reaction of 258 gra~s. The bed was maintained at a temperature of 786C~800C during the reaction.
A total of 1.57 moles of tribromosilane was introduced into the reactor during the run. Removal of the silicon particles at the end of the run showed that the bed had a mass of 268.1 grams or a weight gain of lO.l grams or a yield of 91%, based on the decomposition reaction 4HSiBr3 > Si + 3SiBr4 t 2H2 The invention provides, therefore, a low-temperature, closed-loop continuous process for the economical production of high purity semiconductor grade silicon. The process of the inven-tion, as described, utilizes the direct thermal decomposition of trihalosilane at relatively low temperatures (below 900C) to pro-duce ultra-pure silicon. The process also avoids silicon wall ~15 build-up in the reactor by maintaining a temperature differential ; ~between the bed and the surrounding wall such that the lowest temperature of the wall is above the threshold temperature at which silicon is deposited thereon.
~, .
It will be appreclated that although a particular embodi-ment of the invention has been shown and described, modifications may be made. It is intended in the claims to cover the modifications which come within the true spirit and scope of the invention.
.
'
Claims (4)
1. In a process for producing high purity silicon by the thermal decomposition of halosilane, the improvement comprising:
passing tribromosilane substantially undiluted through a bed of high purity silicon substrate particles in a walled product reactor at a reaction temperature of from about 600 to about 800 degrees C., a pressure of at least about atmospheric pressure and while the temperature of the walls of the product reactor is above the reaction temperature, thereby effecting thermal decomposition of said tribromosilane to deposit high purity polycrystalline silicon on said substrate particles and to produce silicon tetrabromide and hydrogen as reaction products without the production of silicon polymers as an explosive byproduct and amorphous silicon as a clogging byproduct, the reactor product wall temperature such as to prevent accumulation of product reactor wall scale.
passing tribromosilane substantially undiluted through a bed of high purity silicon substrate particles in a walled product reactor at a reaction temperature of from about 600 to about 800 degrees C., a pressure of at least about atmospheric pressure and while the temperature of the walls of the product reactor is above the reaction temperature, thereby effecting thermal decomposition of said tribromosilane to deposit high purity polycrystalline silicon on said substrate particles and to produce silicon tetrabromide and hydrogen as reaction products without the production of silicon polymers as an explosive byproduct and amorphous silicon as a clogging byproduct, the reactor product wall temperature such as to prevent accumulation of product reactor wall scale.
2. The process of claim 1 wherein the bed of high purity silicon substrate particles is a moving or fluid bed and the product reactor wall temperature is at least about 900 degrees C. thereby preventing accumulation of product reactor wall scale.
3. In a process for producing high purity silicon by the thermal decomposition of halosilane, the improvement comprising the steps of:
(a) providing tribromosilane by reacting silicon, silicon tetrabromide and hydrogen in a synthesis reactor at a temperature of from about 450 to about 650 degrees C.;
(b) separating tribromosilane produced in step (a) from reagents and other reaction products of step (a);
(c) passing said separated tribromosilane from step (b) substantially undiluted through a bed of high purity silicon substrate particles in a walled product reactor at a reaction temperature of from about 600 to about 800 degrees C., a pressure of at least about atmospheric pressure, and while the temperature of the walls of the product reactor is above the reaction temperature; thereby effecting thermal decomposition of said tribromosilane to deposit high purity polycrystalline silicon on said substrate particles and to produce silicon tetrabromide and hydrogen as reaction products without the production of silicon polymers as an explosive byproduct and amorphous silicon as a clogging byproduct, the reactor product wall temperature such as to prevent the accumulation of reactor product wall scale; and (d) feeding hydrogen and silicon tetrabromide byproducts from step (c) into the synthesis step (a).
(a) providing tribromosilane by reacting silicon, silicon tetrabromide and hydrogen in a synthesis reactor at a temperature of from about 450 to about 650 degrees C.;
(b) separating tribromosilane produced in step (a) from reagents and other reaction products of step (a);
(c) passing said separated tribromosilane from step (b) substantially undiluted through a bed of high purity silicon substrate particles in a walled product reactor at a reaction temperature of from about 600 to about 800 degrees C., a pressure of at least about atmospheric pressure, and while the temperature of the walls of the product reactor is above the reaction temperature; thereby effecting thermal decomposition of said tribromosilane to deposit high purity polycrystalline silicon on said substrate particles and to produce silicon tetrabromide and hydrogen as reaction products without the production of silicon polymers as an explosive byproduct and amorphous silicon as a clogging byproduct, the reactor product wall temperature such as to prevent the accumulation of reactor product wall scale; and (d) feeding hydrogen and silicon tetrabromide byproducts from step (c) into the synthesis step (a).
4. The process of claim 3 wherein the bed of high purity silicon substrate particles is a moving or fluid bed and the product reactor wall temperature is at least about 900 degrees C. thereby preventing accumulation of product reactor wall scale.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US93500978A | 1978-08-18 | 1978-08-18 | |
| US935,009 | 1978-08-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145117A true CA1145117A (en) | 1983-04-26 |
Family
ID=25466438
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000327660A Expired CA1145117A (en) | 1978-08-18 | 1979-05-15 | Process for producing polycrystalline silicon |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5527890A (en) |
| CA (1) | CA1145117A (en) |
| DE (2) | DE2954368C2 (en) |
| FR (1) | FR2433479B1 (en) |
| GB (1) | GB2028289B (en) |
| IT (1) | IT1193203B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9023297B2 (en) | 2009-07-08 | 2015-05-05 | Schmid Silicon Technology Gmbh | Method and system for producing monosilane |
Families Citing this family (24)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4676967A (en) * | 1978-08-23 | 1987-06-30 | Union Carbide Corporation | High purity silane and silicon production |
| US4374182A (en) * | 1980-07-07 | 1983-02-15 | Dow Corning Corporation | Preparation of silicon metal through polymer degradation |
| US4390510A (en) | 1982-02-16 | 1983-06-28 | General Electric Company | Process for treating spent silicon-containing reaction masses to produce halosilanes |
| JPS61101410A (en) * | 1984-10-24 | 1986-05-20 | Hiroshi Ishizuka | Production of polycrystalline silicon and apparatus therefor |
| US4696834A (en) * | 1986-02-28 | 1987-09-29 | Dow Corning Corporation | Silicon-containing coatings and a method for their preparation |
| US4743344A (en) * | 1986-03-26 | 1988-05-10 | Union Carbide Corporation | Treatment of wastes from high purity silicon process |
| US4871524A (en) * | 1987-09-03 | 1989-10-03 | Ethyl Corporation | Hydrogen purification process |
| EP1786730A2 (en) * | 2004-07-16 | 2007-05-23 | Institutt For Energiteknikk | Method and reactor for continuous production of semiconductor grade silicon |
| WO2007120871A2 (en) * | 2006-04-13 | 2007-10-25 | Cabot Corporation | Production of silicon through a closed-loop process |
| US7935327B2 (en) * | 2006-08-30 | 2011-05-03 | Hemlock Semiconductor Corporation | Silicon production with a fluidized bed reactor integrated into a siemens-type process |
| US7656661B2 (en) * | 2007-07-31 | 2010-02-02 | Donald Shaum | Electronic apparatus with multiple data input modes |
| DE102008017304A1 (en) * | 2008-03-31 | 2009-10-01 | Schmid Silicon Technology Gmbh | Process and plant for the production of ultrapure silicon |
| DE102009037154B3 (en) * | 2009-08-04 | 2010-12-09 | Schmid Silicon Technology Gmbh | Process for the preparation of monosilane |
| DE102009037155B3 (en) * | 2009-08-04 | 2010-11-04 | Schmid Silicon Technology Gmbh | Process and plant for the production of trichlorosilane |
| DE102010000981A1 (en) | 2010-01-18 | 2011-07-21 | Evonik Degussa GmbH, 45128 | Closed-loop process for the production of trichlorosilane from metallurgical silicon |
| DE102010034469A1 (en) | 2010-08-06 | 2012-02-09 | Schmid Silicon Technology Gmbh | Plant for the production of monosilane |
| CN103153855A (en) * | 2010-10-22 | 2013-06-12 | Memc电子材料有限公司 | Production of polycrystalline silicon in substantially closed-loop processes and systems |
| US8449848B2 (en) | 2010-10-22 | 2013-05-28 | Memc Electronic Materials, Inc. | Production of polycrystalline silicon in substantially closed-loop systems |
| US20120100061A1 (en) | 2010-10-22 | 2012-04-26 | Memc Electronic Materials, Inc. | Production of Polycrystalline Silicon in Substantially Closed-loop Processes |
| DE102011089695A1 (en) | 2011-12-22 | 2013-06-27 | Schmid Silicon Technology Gmbh | Reactor and process for the production of ultrapure silicon |
| DE102015203618A1 (en) | 2015-02-27 | 2016-09-01 | Schmid Silicon Technology Gmbh | Column and process for the disproportionation of chlorosilanes to monosilane and tetrachlorosilane and plant for the production of monosilane |
| DE102015209008A1 (en) | 2015-05-15 | 2016-11-17 | Schmid Silicon Technology Gmbh | Process and plant for the decomposition of monosilane |
| WO2017183487A1 (en) * | 2016-04-21 | 2017-10-26 | 株式会社トクヤマ | Metal powder production method |
| DE102019209898A1 (en) | 2019-07-04 | 2021-01-07 | Schmid Silicon Technology Gmbh | Apparatus and method for forming liquid silicon |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2595620A (en) * | 1948-11-27 | 1952-05-06 | Union Carbide & Carbon Corp | Hydrogenation of halogenosilanes |
| BE554836A (en) * | 1956-02-11 | |||
| BE571013A (en) * | 1957-09-07 | |||
| US3012861A (en) * | 1960-01-15 | 1961-12-12 | Du Pont | Production of silicon |
| GB1498266A (en) * | 1974-05-13 | 1978-01-18 | Texas Instruments Inc | Method of silicon production |
| DE2620739A1 (en) * | 1976-05-11 | 1977-12-01 | Wacker Chemitronic | PROCESS FOR PRODUCING HIGHLY PURE SILICON |
| US4117094A (en) * | 1977-06-13 | 1978-09-26 | Texas Instruments Incorporated | Process for silicon and trichlorosilane production |
-
1979
- 1979-05-04 GB GB7915583A patent/GB2028289B/en not_active Expired
- 1979-05-11 DE DE2954368A patent/DE2954368C2/en not_active Expired
- 1979-05-11 DE DE2919086A patent/DE2919086C2/en not_active Expired
- 1979-05-15 CA CA000327660A patent/CA1145117A/en not_active Expired
- 1979-05-16 FR FR7912469A patent/FR2433479B1/en not_active Expired
- 1979-05-17 IT IT22753/79A patent/IT1193203B/en active
- 1979-05-17 JP JP5980079A patent/JPS5527890A/en active Granted
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9023297B2 (en) | 2009-07-08 | 2015-05-05 | Schmid Silicon Technology Gmbh | Method and system for producing monosilane |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2433479A1 (en) | 1980-03-14 |
| DE2954368A1 (en) | 1984-07-12 |
| IT7922753A0 (en) | 1979-05-17 |
| JPS6228083B2 (en) | 1987-06-18 |
| IT1193203B (en) | 1988-06-15 |
| DE2954368C2 (en) | 1986-10-16 |
| DE2919086C2 (en) | 1986-10-16 |
| FR2433479B1 (en) | 1985-10-18 |
| GB2028289B (en) | 1982-09-02 |
| JPS5527890A (en) | 1980-02-28 |
| DE2919086A1 (en) | 1980-03-06 |
| GB2028289A (en) | 1980-03-05 |
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