WO2008042445A2

WO2008042445A2 - Systems and methods for production of semiconductor and photovoltaic grade silicon

Info

Publication number: WO2008042445A2
Application number: PCT/US2007/021397
Authority: WO
Inventors: Steven C. Shatas; David A. Rockstraw
Original assignee: Silicon Solar, Inc.
Priority date: 2006-10-03
Filing date: 2007-10-03
Publication date: 2008-04-10
Also published as: WO2008042445A3

Abstract

The present disclosure provides systems and methods for producing monosilane, purifying silicon, and producing semiconductor and/or photovoltaic grade silicon. Various systems and methods of producing monosilane or purifying silicon are performed by producing methoxysilane intermediates.

Description

SYSTEMS AND METHODS FOR PRODUCTION OF SEMICONDUCTOR AND

PHOTOVOLTAIC GRADE SILICON

Field of the Invention

The present disclosure relates generally to systems and methods for producing semiconductor and photovoltaic grade silicon. More specifically, the present disclosure relates to systems and methods for the production of semiconductor and photovoltaic grade silicon from metallurgical grade silicon via a methoxysilane intermediate.

Background of the Invention

Development of photovoltaics (PV) or solar cells has attracted significant interest and effort as the urgent need for alternative sources of energy become clear. As the solar energy industry continues to grow, a significant increase in the demand for polysilicon feedstock is expected. Recently, the cost of polysilicon as a raw material has soared. Polysilicon as a feed material for semiconductor processing has increased; however increased demand from aggressive expansion in photovoltaics has resulted in polysilicon shortages and significantly increased prices.

To date, silicon is the primary photovoltaic material, with single crystal silicon, multi-crystal silicon and amorphous silicon comprising the majority of the PV market. Currently, PV and electronics-grade silicon are widely produced from hydrogen reduction of trichlorosilane. Trichlorosilane is generally obtained from metallurgical- grade silicon feedstock which has been mined from quartzite. This process suffers from a number of limitations. The process consumes large amounts of energy and is wasteful. Moreover, the process produces toxic by-products which create environmental and safety hazards. For example, chlorosilane intermediates are formed which are both toxic and corrosive. It is clear that the development of new systems and methods for producing photovoltaic and electronics grade silicon is greatly needed. These and other needs are addressed by in present disclosure.

Summary

hi general the present disclosure provides systems and methods for producing purifying silicon. More specifically, the present disclosure relates to systems and methods for the production of semiconductor and photovoltaic grade silicon from silicon- containing compounds via a methoxysilane intermediate.

In one aspect, the present disclosure broadly provides a method of producing polysilicon from silicon characterized in that: organosilicones are used to produce silane which is then thermally decomposed to produce silicon.

In one aspect, the disclosure is directed to methods of producing monosilane. A silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane, and hydrogen. The dimethoxysilane and/or trimethoxysilane is then catalytically disproportionated to form monosilane and tetramethoxysilane. hi certain variations, the tetramethoxysilane can be removed from the monosilane.

In another aspect, the disclosure is directed to a method of purifying silicon by thermally decomposing monosilane to form high purity silicon and hydrogen.

In a further aspect, the disclosure is directed to a method of purifying silicon by reacting a silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane, and hydrogen. The dimethoxysilane and/or trimethoxysilane is catalytically disproportionated to form monosilane and tetramethoxysilane. The monosilane is then thermally decomposed to form silicon and hydrogen. In certain variations, the silicon-containing compound can be metallurgical silicon or ferrosilicon. In other variations, the catalyst is copper. In further variations, the a zinc and/or aluminum promoter is included with the copper catalyst.

In various aspects, the methanol can be combined with an inert gas before reacting the silicon-containing compound with methanol.

In other variations, the dimethoxysilane and/or trimethoxysilane are catalytically disproportioned in the presence of a base catalyst. In certain preferred embodiments, the catalyst is a potassium-fluoride loaded alumina catalyst.

In various aspects, the purified silicon can be single crystal silicon, multi-crystal silicon or amorphous silicon.

The silicon can be used as a feedstock for the production of photovoltaics, semiconductors or solar cells.

The disclosure is further directed to systems for producing monosilane and/or liquid silicon. In one embodiment, the system includes a reactor configured to contact metallurgical silicon and methanol to form dimethoxysilane and/or trimethoxysilane, and hydrogen. The reactor operably associated with a disproportionation reactor configured to disproportionate the dimethoxysilane and/or trimethoxysilane to form monosilane and tetramethoxysilane. The disproportionation reactor is operably associated with a thermal reactor configured to produce liquid silicon from said monosilane. These reactors are "operably associated" in that they can be connected directly, or various additional components can be placed between them.

The disclosure is further directed to high temperature thermal reactors for producing liquid silicon from a silicon-containing gaseous precursor. In certain variations, the high temperature thermal reactor includes a thermal reaction chamber operably associated with a coaxial injector. The coaxial injector includes an inner tubular member configured to transport the silicon-containing gaseous precursor into the thermal reaction chamber, and an outer tubular member configured to transport an inert gas into the reaction chamber. In certain variations, the coaxial injector is disposed in the lower half of the thermal reaction chamber. In further variations, the high temperature thermal reactor includes an exhaust outlet disposed at the top of the a thermal reaction chamber.

Brief Description of the Drawings

These and various other features and advantages of the inventions will be apparent upon reading of the following detailed description in conjunction with the accompanying drawings and the appended claims provided below, in which:

FIG. 1 depicts a process flow diagram illustrating a system according to one embodiment of the present disclosure;

FIG. 2 depicts a process flow diagram showing methanol/TTMS recovery according to one embodiment of the present disclosure; and

FIG. 3 depicts a process flow diagram showing silane synthesis and decomposition according to one embodiment of the present disclosure. FIG. 4A depicts high temperature thermal control reactor. FIG. 4B depicts a perspective view of a coaxial injector. FIG. 4C depicts a cut-away view of a coaxial injector.

Detailed Description of the Invention

The disclosure relates generally to systems and methods for producing monosilane, purifying silicon (such as semiconductor and photovoltaic grade silicon), and systems for performing these methods. More specifically, the disclosure relates to systems and methods for the production of semiconductor and photovoltaic grade silicon from metallurgical grade silicon via a methoxysilane intermediate.

Embodiments of the present disclosure are illustrated in FIGs. 1 to 4. For convenience, system 10 of the present disclosure is shown comprised of subsystems 100, 200 and 300. While one specific process flow is shown, it should be understood by those of skill in the art that other configurations may be used according to the present teaching, and that the invention is not limited to the specific configuration described herein.

Referring to the Figures, FIG. 1 illustrates one embodiment of a process feed and methoxylation reaction system of the present disclosure. FIG. 2 shows one embodiment of a methanol (MeHO) and tetramethoxysilane (TTMS) recovery system of the present disclosure, and FIG. 3 illustrates one embodiment of a silane synthesis and decomposition reaction system (silane/PVSi) of the present disclosure.

A methoxylation reaction is carried out in the subsystem 100 illustrated in FIG. 1.

Specifically, a silicon-containing compound (e.g. metallurgical silicon (MGSi)) is converted into a mixture of methoxysilanes. A feed stream is conveyed to a first reactor stage, a fluidized bed reactor 126. The feed stream generally comprises a mixture of fresh and recycled components, and includes one or more of the materials provided in individual feed streams as shown in Table 1 below:

Table 1 - Example Feed to Reactor R-IOl

As a non-limiting example, in the process for producing monosilane gas disclosed by this invention, the intermediate di- and tri-methoxysilane is produced in a fluidized bed reactor by the catalyzed direct reaction of methanol vapor and a contact mass of silicon-containing compound (e.g. powdered metallurgical grade silicon) intimately mixed with copper catalyst and optionally a zinc/aluminum catalyst promoter. Referring to FIG. 1, the feedstock liquid methanol 102 is mixed in a mixer 104 with a liquid methanol 205 recycled from a distillation tower 210 used in subsection 200 (see FIG. 2). The resulting liquid methanol mix 106 from the mixer 104 is vaporized by a vaporizer 108.

Quantities of copper catalysts are known in the art, as described, for example, by U.S. Patent No. 3,072,700. In some instances, copper can be 2-30 wt%, and preferably 8- 10 wt %. IN some instances, Zinc/ Aluminum promoter is 0.01-0.5 wt%, and preferably 0.1 wt %.

Hydrogen gas reactant 110 is mixed with compressed recycled hydrogen 112 from a compressor 114 in another mixer 116. The hydrogen gas mixture output 118 is mixed with the methanol vapor 120 produced from the vaporizer 108 in a mixer 122 and the mixed hydrogen/methanol vapor output 124 of the mixer 122 is fed into a heated fluidized bed reactor 126 and acts as the fluidizing medium for the fluidized bed reactor 126.

Silicon-containing compound 128 (e.g. powdered metallurgical silicon) is mixed in a mixer 130 with a copper catalyst and zinc/aluminum promoter blend 132. Also mixed in mixer 130 is a mixture 134 of recycled catalyst 138 and a zinc/aluminum promoter blend 140, which was mixed using a mixer 142. The resulting silicon- containing composition/catalyst/activator particles 144 are fed into the heated fluidized bed reactor 126 as the contact mass. The contact mass is fluidized by the flow of mixed hydrogen gas 118 and methanol vapor 120, and the methanol vapor 120 reacts with silicon particles 144 in the fluidized bed reactor 126 to produce a mixture 146 of dimethoxysilane, trimethoxysilane, and tetramethoxysilane vapors mixed with un-reacted methanol vapor and hydrogen gas. The vapor output 146 of the fluidized bed reactor 126 is partially condensed by a condenser 148 and then fed into a low temperature flash drum 150, where the liquids 156 are separated from the hydrogen gas 152.

Generally, the reactor effluent is cooled, and partially condensed in the heat exchanger 148 before being conveyed to the low temperature flash drum 150, where hydrogen is removed and recycled to the reactor feed through compressor 114. The hydrogen gas output 152 of the flash drum 150 passes into the input of a compressor 114 through a purge valve 154, where a portion 160 of the hydrogen is purged in order to remove impurities in the gas. Additionally, a heater 158 may be used to warm the recycled hydrogen gas 162 to create warm recycled hydrogen gas 164 prior to compression to minimize condensation from occurring within the compressor.

Catalyst solids may be recycled within the fluidized bed reactor 126, and are represented in the flow diagram as 138 for material balance equations. The reacted contact mass particles are depleted in their silicon content and become lighter and rise to the top of the fluidized bed, where a portion of the reacted contact mass is removed and fed into a mixer 142 as recycled catalyst 138.

A skilled artisan will recognize that the individual feed streams may be adjusted to provide desired totals of the fresh and recycle feeds to the fluidized bed reactor 126. Some of the materials may be in solid form and in such instance are generally carried in a separate substream from the VLE-based components. A fluidized bed or vibrating bed reactor may be employed to transport the solid components.

In the exemplary embodiment the VLE feed mixture is vaporized in a shell and tube heat exchanger to 150⁰C using a low-pressure steam utility. The vapor is subsequently fed to the methoxylation reactor where a silicon-containing compound is catalytically converted to a mixture of di-, tri-, and tetramethoxysilane in a hydrogen atmosphere. The chemical reactions are summarized in the following stoichiometric equations: 4 CH₃OH + Si → (CH 3O)₄ Si + H₂ 0)

3 CH₃OH + Si → (CH 3O)₃ SiH + H₂ (2)

2 CH₃OH + Si → (CH 3O)₂ SiH_: > (3)

Catalyst solids may be recycled within the fluidized bed reactorl26, and are represented in the flow diagram as 138 for material balance equations.

Referring to FIG. 2, liquid bottoms 156 from flash drum 150 are conveyed to subsystem 200 for separation, and are pumped by a centrifugal pump 202 to stage 9 of a distillation tower 206. The distillation tower 206 represents a 22-stage sieve tray column in the exemplary embodiment. This column is preferably configured to break the trimethoxysilane / methanol azeotrope using tetramethoxysilane solvent fed to stage 3 of the distillation tower 206, and to recover about 97 mol % of the methanol in the overheads of the column, hi other embodiments, a more rigorous separation of methanol may be achieved at this stage using a larger column.

The overheads from the distillation tower 206 are condensed in a condenser 208 which also co-condenses the product dimethoxysilane 211. Methanol is recovered with dimethoxysilane, and in a preferred embodiment, the condensed mixture of methanol and dimethoxysilane 211 is fed into stage 10 of a distillation tower 210. The distillation tower 210 may be a 20 -stage sieve tray column with feed to stage 10. This column is preferably configured to recover about 99.9 mol% of dimethoxysilane in the bottoms of the column(recovered at about 98 mol% purity), and about 99% of the methanol in the overheads of the column (recovered at 95% purity with the balance being primarily tri- and tetramethoxysilane). The bottoms from the distillation tower 210 are cooled by a heat exchanger 212 and the recovered liquid methanol 205 is recycled to the mixer 104 in subsystem 100 (see FIG. 1).

The overheads from the distillation tower 210 are condensed by a condenser 214 and the recovered liquid dimethoxysilane 216 is fed into a mixer 218. The bottoms from the distillation tower 206 are condensed in a condenser 220 and fed into stage 10 of a distillation tower 222. In an exemplary embodiment, the distillation tower 222 is a 24 stage sieve tray column, configured to separate about 99 mol % of trimethoxysilane from the tetramethoxysilane used to break the azeotrope. Trimethoxysilane purity is about 90 mol %, with tetramethoxysilane as the primary contaminate which is subsequently removed from the silane in a later stage.

The tetramethoxysilane bottoms from the distillation tower 222 are cooled by a heat exchanger 224 and the liquid tetramethoxysilane (TTMS; 226) is fed into a purge valve 228 were a portion of the TTMS 229 is purged to remove impurities. The remainder of the tetramethoxysilane 230 is pumped by a centrifugal pump 232 into stage 3 of the distillation tower 206.

The overheads from the distillation tower 222 are condensed by a condenser 234 and the liquid trimethoxysilane 236 is fed to a mixer 218 where it is mixed with dimethoxysilane 216 to form a mixture 238.

The di- and trimethoxysilane streams 238 are fed to subsection 300 of the system (see FIG. 3), where the silicates are catalytically disproportionated in a disproportionation reactor 304 to silane according to the following chemical reactions:

4 (CH₃O)₃ SiH → 3 (CH₃O)4Si + SiH₄ (4)

2 (CH₃O)₂ SiH₂ → (CH₃O)₄ Si + SiH₄ (5)

In a nonlimiting exemplary embodiment, the mixed di- and tri-methoxysilanes

238 are pumped by a centrifugal pump 302 into a disproportionation reactor 304. This disproportionation reactor 304 may be a fixed bed catalytic reactor using a potassium-fluoride loaded alumina catalyst. The di- and tri-methoxysilanes disproportionate in the catalytic reactor 304 and form product monosilane gas and the by-product tetramethoxysilane. Various other catalysts can be used in place of potassium-fluoride loaded alumina catalyst. Any basic compound can be used as a catalyst. In certain other preferred embodiments, sodium' methoxide can be used. Various additional catalysts are disclosed, for example, in U.S. Patent No. 4,959,200 to Inaba et. al.

Gas-phase silanes are then phase-separated from liquid TTMS, and then fed into a reactor where they are decomposed into polysilicon and hydrogen gas, according the chemical reaction:

SiH₄ → Si + 2 H₂ (6)

The silicon produced may be further processed to form solar wafers. In one embodiment further processing may include polycrystalline ingot casting and sawing of the material into individual wafers.

In a nonlimiting example, the output 303 of reactor 304 may be fed into a flash drum 308 where the monosilane gas is removed. The liquid bottoms from the flash drum 308 are recovered as by-product tetramethoxysilane 310. Further, the gaseous monosilane 312 produced in the catalytic reactor 304 and removed by the flash drum 308 is compressed by a compressor 314 and fed into a silane gas purifier 316, which removes residual impurities from the monosilane gas. The purifier 316 comprises a series of solid bed absorber materials for selectively removing deleterious impurities such as diborane and phosphine from the monosilane gas. The output of the purifier 316 is ultrapure monosilane gas 318 suitable for producing thin-film silicon electronic materials or thin film silicon photovoltaic products such as amorphous silicon photovoltaic cells.

Additionally, the purified monosilane gas output 318 of the purifier 316 may be fed into a reactor 320, a high temperature reactor where the silane is converted into liquid silicon 322 and gaseous hydrogen 324. The gaseous hydrogen by-product is recovered and the liquid silicon is used to produce single-crystal ingots suitable for electronic and photovoltaic applications or multicrystalline silicon ingots suitable for producing multicrystalline photovoltaic silicon solar cells.

In a preferred embodiment, reactor 322 is reactor 400; a detailed view of reactor 400 is shown in FIG. 4A. Reactor 400 is a high temperature thermal reactor apparatus capable of producing liquid silicon from a silicon-containing gaseous precursor. This process is also referred to as thermally decomposing silane to produce silicon. Reactor 400 includes high temperature thermal reaction chamber 415 defined by walled enclosure 401, and coaxial injector 405.

Walled enclosure 401 is surrounded by heater 413. Heater 413 is configured to elevate thermal reactor chamber 415 above the melting point of silicon. The temperature can be mainted during introduction, reaction and decomposition of a silicon-containing precursor gas. Those of skill in the art will understand that any heating system known in the art can be used.

Silicon-containing gas precursor is added to reaction chamber 415 via injector coaxial injector 405. Turning to FIGS. 4B and 4C, silicon-containing gas precursor enters via silicon gas port 402, and flows through inner tubular member 406. A second gas stream of inert or reactive non-silicon containing gas enters via port 403 and flows through outer tubular member 407 between the inside surface of outer tubular member 407 and outer surface of inner tubular member 406. Outer jacket 408 surrounds outer tubular member 407. Cooling media enters and exits via ports 409a and 409b. The cooling media maintains the temperature of the inert or reactive non-silicon containing gas at a temperature substantially below the decomposition temperature of the silicon- containing gas. Both the silicon-containing gas precursor and the second gas stream are introduced into high temperature thermal reaction chamber 415.

Referring again to FIG. 4A,coaxial injector 405 includes thermal insulator 410 disposed between reactor chamber 415 and coaxial injector 405. The thermal insulator surface of thermal insulator 410 that is adjacent to high temperature thermal reactor chamber 415 is capable of being maintained above the melting point of silicon. The thermal insulator surface of thermal insulator 410 that is adjacent to coaxial injector 405 is capable of being maintained at a temperature substantially below the decomposition temperature of said silicon-containing gas.

Reaction chamber 415 is maintained at a temperature at or above the melting point of silicon during introduction, reaction and decomposition of the silicon-containing precursor gas and second inert or reactive non-silicon containing gas by heater 413.

Reaction products leave reaction chamber 415 vial by-product outlet 411. By products form by the reaction and/or decomposition of silicon-containing gaseous precursor and second inert or reactive non-silicon containing gas positioned in high temperature reaction chamber 415. Substantially all reaction products and second inert or reactive non-silicon containing gas can be removed substantially independently of liquid silicon product.

Liquid silicon leaves the reaction chamber via liquid silicon outlet 412. The position of liquid silicon outlet 412 at the bottom of reaction chamber 415 allows a much higher quantity of liquid silicon to be recovered.

Coaxial injector 405 of the silicon-containing gas precursor provides the advantage that contaminants do not enter the precursor stream before entering reactor. The precursor stream is surrounded by the inert gas as it enters the reactor. The inert gas does not react with the precursor stream. As such, the silicon produced by the method is substantially more pure. Further, the flow of the inert gas stream helps reduce plugging of thermal insulator 410.

Those of skill in the art will understand that any inert gas can be used. Inert gases include, but are not limited to, hydrogen, helium, and argon. In preferred embodiments, the inert gas is hydrogen. By injecting methanol inside a flow of inert gas, contaminants are prevented from entering reactor 100 during the transfer process. Although coaxial injector 405 of FIG. 4A is depicted as disposed in the sidewall of reaction chamber 415, those of skill in the art will recognize that coaxial injector 405 can be disposed at any position in said reaction chamber 415. In preferred embodiments, coaxial injector 405 is positioned in the lower half of the reaction chamber. This positioning allows the silicon gas to flow to the bottom of the reaction chamber more readily.

The location of by-product outlet 411 also provides for increased purity. The inert gas, as well as gaseous by-products, expand and rise when heated. When the gaseous by-products reach the top of reaction chamber 415, the by-products leave chamber 415. The position the by-product outlet 411 thus provides that a greater proportion of by-products leave the reaction chamber, and that the purified silicon will have increased purity.

Reactor 400 can also be configured independently of the embodiments of FIGS.

1-3. The skilled artisan will recognize that monosilane can be produced by other methods than disclosed above before being introduced to reactor 400. For example, monosilane gas can be produced by the catalytic disproportionation by the Union Carbide process as disclosed, for example, in US Pat. 3,968,199 to Bakay, which is incorporated by reference herein in its entirety. Other methods of producing monosilane gas include the sodium aluminum hydride reduction of silicon tetrafluoride by the Ethyl process as disclosed in US Pat. 4,632,816 to Marlett, also incorporated herein by reference in its entirety. Another method of producing monosilane gas is the catalytic disproportionation of triethoxysilane as disclosed in US Pat. 6,103,942 to Tsuo et. al.

In another embodiment, the present disclosure provides a method of producing polysilicon comprising the steps of: reacting a silicon-containing compound and methanol to form trimethoxysilane and hydrogen. Trimethoxysilane undergoes disproportionation to form silane and tetramethoxysilane. The silane is thermally decomposed to form silicon and hydrogen. The formed polysilicon according the present disclosure is particularly useful as a feedstock for photovoltaic solar cells and may be formed as single crystal silicon, multicrystal silicon, or amorphous silicon. The formed polysilicon according to the present disclosure is also useful as a feedstock for semiconductor processing. Solar and photovoltaic cells can be produced by any methods known in the art, for example as described in Solar Cell: US Patent. No. 3,990,097 to Lindmayer, incorporated herein by reference in its entirety.

Crystals can be prepared by any method known in the art. For example, silicon crystals can be preared by crystal pulling apparatus as described, for example, in US

Patent No. 2,892,739 to Rusler and/or U.S. Patent No. 4,036,595 to Lorenzini et. al., each of which is incorporated herein by reference in its entirety. Multicrysalline silicon can by performed by the methods and casting apparatus described in U.S. Patent No. 4,175,610 to Zauhar et. al., which is incorporated herein by reference in its entirety. Silicon crystals,amorphous silicon, and single crystal silicon may also be formed as described in O'Mara, William C, Handbook of Semiconductor Silicon Technology, 1990, Noyes Publications, which is incorporated herein by reference in its entirety.

The present methods and systems produce high purity silicon. Electronic applications generally require a "high purity" silicon of 11 nines purity (i.e. total impurity levels of less than a few parts per billion). The silicon purity can be relaxed somewhat for silicon used for photovoltaic (PV) applications, in this case a purity of 6-7 nines (total impurity levels of less than about 10 parts per million, except for the donor and acceptor elements such as boron, phosphorous, arsenic and antimony, which must be controlled to sub parts per million levels).

Moreover, the systems and methods of the present disclosure produce silicon at a much lower energy cost than traditional silicon production methods, hi one example, the method of the present disclosure was carried out at an energy consumption per kg of silicon produced of about 35 kWh/kg. Methods of using the produced silicon in the production of semiconductors, photovoltaic cells, or solar cells can be accomplished by any methods known in the art.

All publications referenced herein are hereby incorporated by reference in their entirety.

The foregoing description of specific embodiments of the invention has been presented for the purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications, embodiments, and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

The ClaimsWhat is claimed is:

1. A method of producing monosilane comprising: a) reacting a silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane; and b) catalytically disproportionating said dimethoxysilane and/or trimethoxysilane to form monosilane.

2. The method of claim 1, further comprising c) removing any tetramethoxysilane from said monosilane.

3. A method of purifying silicon comprising thermally decomposing monosilane to form silicon.

4. A method of purifying silicon comprising: a) reacting a silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane; b) catalytically disproportionating said dimethoxysilane and/or trimethoxysilane to form monosilane; and c) thermally decomposing the monosilane to form silicon and hydrogen.

5. The method of claim 1 , 2 or 4, wherein the silicon-containing compound is selected from the group consisting of metallurgical silicon and ferrosilicon.

6. The method of claim 1, 2 or 4, wherein said step a) comprises reacting said silicon and said methanol in the presence of a copper catalyst.

7. The method of claim 1 , 2 or 4 wherein said step a) further comprises reacting said silicon-containing compound and said methanol in the presence of a copper catalyst and a zinc/aluminum promoter.

8. The method of claim 1 , 2 or 4, wherein said methanol is combined with an inert gas before said step a).

9. The method of claim 1, 2 or 4, wherein said step b) comprises catalytically disproportionating said dimethoxysilane and/or trimethoxysilane in the presence of a potassium-fluoride loaded alumina catalyst.

10. The method of claim 1, 2 or 4, further comprising adding tetramethoxysilane to said dimethoxysilane and/or trimethoxysilane.

11. The method of claim 3 or 4, further comprising purifying said monosilane before thermally decomposing the monosilane.

12. The method of claim 3 or 4 wherein said silicon is formed as single crystal silicon.

13. The method of claim 3 or 4 wherein said silicon is formed as multi-crystal silicon.

14. The method of claim 3 or 4 wherein said silicon is formed as amorphous silicon.

15. The method of claim 1 further comprising using said silicon as a feedstock for the production of photovoltaics.

16. The method of claim 1, further comprising using said silicon as a feedstock for the production of semiconductors.

17. A method of producing a solar cells, comprising the steps of: reacting silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane; trimethoxysilane undergoes catalytic disproportionation to form monosilane; thermally decomposing the monosilane to form silicon and hydrogen; and forming polysilicon solar cells from said silicon.

18. A system for producing liquid silicon comprising: a reactor configured to contact a silicon-containing compound and methanol to form dimethoxysilane and/or trimethoxysilane, and hydrogen, said reactor operably associated with a disproportionation reactor configured to disproportionate said dimethoxysilane and/or trimethoxysilane to form monosilane and tetramethoxysilane, said disproportionation reactor operably associated with a thermal reactor configured to produce liquid silicon from said monosilane.

19. A high temperature thermal reactor for producing liquid silicon from a silicon- containing gaseous precursor, comprising:

a thermal reaction chamber; and

a coaxial injector operably associated with said thermal reaction chamber, said coaxial injector comprising an inner tubular member configured to transport said silicon- containing gaseous precursor into said thermal reaction chamber, and an outer tubular member configured to transport an inert gas into said reaction chamber.

20. The high temperature thermal reactor of claim 19, wherein said coaxial injector is disposed in the lower half of the thermal reaction chamber.

21. A high temperature thermal reactor for producing liquid silicon from a silicon- containing gaseous precursor, comprising:

a thermal reaction chamber comprising an exhaust outlet disposed in the top of said thermal reaction chamber.

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