EP2736845A1

EP2736845A1 - Use of silicon tetrachloride byproducts for producing silicon by reaction with metal reducing agents

Info

Publication number: EP2736845A1
Application number: EP12722738.7A
Authority: EP
Inventors: Ekkehard MÜH; Hartwig Rauleder; Bodo Frings
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2011-07-25
Filing date: 2012-05-23
Publication date: 2014-06-04
Also published as: DE102011109543A1; WO2013013857A1; TW201317180A

Abstract

The invention relates to the use of the byproduct silicon tetrachloride, which forms as a byproduct during the manufacture of silicon or halogen silanes, for producing silicon, wherein the byproduct silicon tetrachloride is converted to silicon and metal chlorides using an elemental, metal reducing agent.

Description

Use of silicon tetrachloride by-products for the production of

Silicon by reaction with metallic reducing agents

The invention relates to the use of the by-product silicon tetrachloride, in particular obtained as a byproduct in the production of silicon or halosilanes, for the production of silicon, by reacting the by-product silicon tetrachloride with an elemental, metallic reducing agent to silicon and metal chlorides. It is known that silicon tetrachloride is obtained as a by-product both in the production of silicon in the context of the Siemens process and in the production of halosilanes, such as trichlorosilane. Trichlorosilane is obtained by reacting crude silicon with hydrogen chloride in the fluidized bed. As a by-product, in this reaction, silicon tetrachloride is usually formed to be 10 to 15%.

Furthermore, it is known to produce silicon, in particular high-purity silicon from chlorosilanes in the presence of hydrogen. These are silicon tetrachloride,

Trichlorosilane and / or dichlorosilane reacted with hydrogen to form silicon and hydrogen chloride. On a large scale, only the Siemens process has gained importance, in which trichlorosilane is used as starting material.

For this purpose, in the fluidized bed gaseous hydrogen chloride at 300 to 350 ° C in a fluidized bed reactor to trichlorosilane HS1CI3 (TCS) reacted and usually pure distilled to separate, inter alia, formed silicon tetrachloride (STC).

Si + 4 HCl -> SiCl ₄ + 2 H ₂ The Tnchlorsilan thus obtained is thermally decomposed in the presence of hydrogen, followed by heated hyperpure silicon rods at 1000 to 1200 ° C to form silicon, silicon tetrachloride and hydrogen chloride.

4 HSiCIs + 2 H ₂ -> 3 Si + SiCl ₄ + 8 HCl

As a by-product of the reaction, silicon tetrachloride is formed. It is known to convert the silicon tetrachloride by reaction with hydrogen back into Tnchlorsilan and feed the Siemens process again. Also in the recycling silicon tetrachloride is again formed from Tnchlorsilan in the synthesis of silicon.

The conversion of monosilane SiH into silicon also proceeds via the production of tochlorosilane, in which silicon tetrachloride is formed as a by-product.

It is also known that silicon dioxide, known as fumed silica, can be produced from silicon tetrachloride. The demand for fumed silica depends on demand and is therefore tied to market conditions, so that the demand is not unlimited.

All mentioned uses have in common that the reconversion of

Silicon tetrachloride in Tnchlorsilan is energetically and economically expensive.

A particular disadvantage is that not only silicon but also silicon tetrachloride is formed from the Tnchlorsilan, so that this cycle the

Making silicon expensive and expensive. The object of the present invention was to provide a further economical use of silicon tetrachloride by-products, which are the abovementioned

Disadvantages does not have and preferably directly apply, without that cycle again and again, such as the above, must be traversed. Another task was to avoid the use of environmentally harmful compounds, or compounds that are expensive to dispose of. Preferably, a use should be provided which essentially allows the

used reactants exclusively in economically required products. The object of the invention was also the reduction or avoidance of waste and unusable by-products per kilogram of hyperpure silicon in the implementation of the Siemens process. The problem is solved by the use according to the invention

Claim 1. Further preferred embodiments and a detailed

Description can be found in the subclaims and in the description.

The invention relates to the use of silicon tetrachloride, as

By-product is obtained in the production of silicon, monosilane or halosilanes, or generally by silicon tetrachloride by-products for the production of silicon, by the silicon tetrachloride is reacted with an elemental, metallic reducing agent, in particular sodium or zinc, to silicon and metal chlorides. In this case, sodium chloride and / or zinc chloride are obtained as metal chlorides.

SiCl ₄ + 4 Na -> Si + 4 NaCl

SiCl ₄ + 2 Zn -> Si + 2 ZnCl ₂ object of the invention is thus the use of silicon tetrachloride, which is obtained in particular as a by-product in the Siemens process, for the production of silicon by this silicon tetrachloride with an elementary, metallic reducing agent to silicon and the corresponding metal chloride is reacted. Another object of the invention is also the use of

Silicon tetrachloride, which is obtained in particular as a byproduct in the production of halosilanes or monosilane, for the production of silicon by this silicon tetrachloride is reacted with an elemental, metallic reducing agent to silicon and the corresponding metal chloride. As halosilane are SiHal _x H _-x , with shark equal to chlorine and x is 1, 2, 3 or 4, but also

Polyhalosilanes, such as a Halogendisilan, Halogentrisilan and higher halosilanes, but especially hexachlorodisilane. According to the use of the invention it is preferred if the silicon tetrachloride used is an i) by-product of the Siemens process in which silicon is formed from suitable toluene silane by reduction with hydrogen; and / or ii) a by-product of the preparation of silicon-based thiol with hydrogen chloride; and / or a) is a by-product of dismutation reactions in the preparation of monosilane, monochlorosilane, dichlorosilane, tochlorosilane and / or polyhalosilanes. As a polyhalosilane is also a Halogendisilan, Halogentrisilan and higher

Halogensilanes, but especially hexachlorodisilane. If a high-purity silicon tetrachloride is used according to the invention, for example, from one or more of the abovementioned processes, it is preferable to use an equally pure elemental, metallic reducing agent.

It is particularly preferred that the derived from the Siemens process silicon tetrachloride prior to the reaction with an elemental, metallic

Reducing agent does not need to be cleaned again, but directly with the

Reductant, in particular with sodium or zinc, to silicon and metal chloride can be implemented. The silicon thus obtained may, if necessary or desired, be purified by directional solidification or as described below. The metal chlorides are sodium chloride when sodium is used, and zinc chloride when zinc is used.

A particular advantage of the use according to the invention is that the

Silicon tetrachloride, which is obtained as a by-product in the production of silicon, monosilane or halosilanes without further purification, in particular without

previous purification, particularly preferably optionally only with an adsorbent and / or filter is purified and then reacted with an elemental, metallic reducing agent. Elementary, metallic reducing agents according to the invention comprise an alkali metal, an element of the 2nd subgroup of the Periodic Table or a mixture containing at least one of the elements, in particular sodium being used as the reducing agent or zinc used. These are lithium, potassium, sodium, zinc, cadmium or

Mercury. Particularly preferred reducing agents are sodium and zinc.

The use according to the invention is characterized in that the before a reduction of silicon tetrachloride, if necessary, if necessary, metallic impurities, in particular impurities with metallic solids in the silicon tetrachloride by means of filtration, liquid impurities by means of a

Adsorbent, dissolved impurities by means of an adsorbent or impurities by means of a combination of the aforementioned measures before the reaction with the reducing agent are separated. Not reduced

Silicon tetrachloride may also be contacted by means of said measures prior to re-contacting with the elemental metallic reducing agent

Impurities are freed. For filtration of the silicon tetrachloride, a filter preferably has a pore size of less than 100 μιτι on, preferably less than 50 μιτι to 5 μιτι on, more preferably, the filter has a mean pore size between 5 to 30 μιτι, more preferably from 5 to 10 μιτι, optionally can be filtered at least once in a further step, the thus treated silicon tetrachloride, wherein the at least one filter has a pore size of less than 5 μιτι, in particular a pore size less than or equal to 1 μιτι, more preferably a pore size less than or equal 0.1 μιτι, or less than or equal 0,05 μιτι, the content of the filtrate of impurities, such as foreign metals and / or the foreign metal-containing compound is then reduced. When

Foreign metals are all metals, with the exception of silicon. The pore size of the filter can also result from the interparticle packing of an adsorbent.

The adsorbent used is preferably an organic, amino-functionalized, polymeric adsorbent to which the silicon tetrachloride is contacted to reduce the level of impurities, which generally include foreign or foreign metal-containing compounds. The adsorbent used is essentially anhydrous and free of organic solvents. Preferably, an adsorbent comprises a divinylbenzene crosslinked one Polystyrene resin having tertiary amino groups and / or quaternary amino groups, wherein the amino groups are substituted by ethyl or methyl groups. Preferably, Amberlyst A 21 and Amberlyst A 26 OH are both ion exchange resin based on divinylbenzene cross-linked polystyrene resin with trimethylamino- or dimethylamino-functionalized polymeric backbone of the resin.

Likewise provided by the invention is the use of silicon tetrachloride;

in particular that which is obtained as a by-product in the production of silicon, monosilane or halosilanes; for producing silicon by freeing the silicon tetrachloride from metallic impurities, in particular particulate impurities, in the silicon tetrachloride by means of filtration and from liquid or dissolved impurities by contacting with an adsorbent before reacting with the elemental metallic reducing agent, and subsequently treating the silicon tetrachloride thus treated an elemental, metallic reducing agent is reacted. Preferably, the silicon tetrachloride is sodium or zinc

reacted and silicon and the corresponding metal chlorides, sodium chloride and / or zinc chloride obtained.

The reaction of silicon tetrachloride with zinc is preferably carried out in one

Gas phase reactor by adding both gaseous silicon tetrachloride and

gaseous zinc in a 900 to 1 100 ° C hot reaction zone, preferably at 910 to 1090 ° C, registered and intimately mixed. In general, silicon tetrachloride and the reducing agent, in this case zinc, are used in a stoichiometric ratio to each other or preferably silicon tetrachloride is light

Excess to the reducing agent used. From the gas phase reactor, the gaseous by-products and unreacted starting materials are removed and pure silicon is deposited. Zinc chloride can be withdrawn as a gaseous by-product.

When sodium is used for reduction, the temperature in the reaction zone may be between 880 to 2000 ° C. Unreacted silicon tetrachloride may be re-reacted with the reducing agent and optionally purified from dissolved or solid impurities as described above. Subsequently, the silicon obtained by reduction of metals and / or metal salts, the boiling point of which is below the melting point of silicon, can be purified by melting, in particular complete melting, preferably one or more directional solidification processes are subsequently carried out. Preferably, the silicon is purified of sodium chloride, sodium, zinc and / or zinc chloride and other foreign metals by directional solidification. The person skilled in the art is familiar with the various solidification processes, which include zone melting with a constant melt volume, or also the Vertical Bridgman method, Vertical Gradient Freeze method (VGF), Czochralski method or the neck Kyropoulos method. The silicon produced by directional solidification vorzugseise has a resistivity of between 10 ^-2 and 10 ⁴ Ohm x cm.

If the silicon is to be used for solar applications, the silicon produced has to meet particularly stringent purity requirements. Impurities in the starting compounds in the stated field of application are already disturbing in the mg / kg (ppm range), g / kg) ppb to ppt range. Due to their electronic properties, elements of the III and V group of the periodic table interfere particularly, so that for these elements, the limits of contamination in the silicon are particularly low. For example, on the pentavalent phosphorus and arsenic, the doping of the produced silicon caused by them is n-type semiconductor

problematic. The trivalent boron also leads to undesirable doping of the produced silicon, so that a p-type semiconductor is obtained.

For example, there is solar grade silicon (Si _sg ) having a purity of 99.999% (5.9's) or 99.9999% (6.9's). The suitable for the production of semiconductors silicon (electronic grade silicon, Si _eg ) requires an even higher purity.

The invention also relates to the use of the by-product

Silicon tetrachloride for producing high-purity silicon comprising reduction with elemental, metallic reducing agents, preferably with subsequent melting, for example directional solidification processes and / or phase separation, the pure silicon being a silicon having the following impurity profile: Aluminum less than or equal to 5 ppm, or between 5 ppm and 0.0001 ppt, in particular between 3 ppm to 0.0001 ppt, preferably between 0.8 ppm to 0.0001, ppt, more preferably between 0.6 ppm to 0.0001 ppt more preferably between 0.1 ppm to 0.0001 ppt, most preferably between 0.01 ppm and 0.0001 ppt, more preferably 1 ppb to 0.0001 ppt,

a. Boron below 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm to 0.0001 ppt, preferably in the range of 3 ppm to 0.0001 ppt, or more preferably in

Range from 10 ppb to 0.0001 ppt, more preferably in the range of 1 ppb to 0.0001 ppt

b. Calcium less than or equal to 2 ppm, preferably between 2 ppm and 0.0001 ppt,

in particular between 0.3 ppm and 0.0001 ppt, preferably between 0.01 ppm and 0.0001 ppt, particularly preferably between 1 ppb and 0.0001 ppt,

c. Iron less than or equal to 20 ppm, preferably between 10 ppm and 0.0001 ppt,

especially between 0.6 ppm and 0.0001 ppt, preferably between 0.05 ppm to 0.0001 ppt, more preferably between 0.01 ppm to 0.0001 ppt, and most preferably 1 ppb to 0.0001 ppt;

d. Nickel less than or equal to 10 ppm, preferably between 5 ppm and 0.0001 ppt,

in particular between 0.5 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, more preferably between 0.01 ppm and 0.0001 ppt, and very particularly preferably between 1 ppb and 0.0001 ppt

e. Phosphorus less than 10 ppm to 0.0001 ppt, preferably between 5 ppm to 0.0001 ppt, in particular less than 3 ppm to 0.0001 ppt, preferably between 10 ppb to 0.0001 ppt and most preferably between 1 ppb to 0.0001 ppt

f. Titanium less than or equal to 2 ppm, preferably less than or equal to 1 ppm to 0.0001 ppt,

in particular between 0.6 ppm to 0.0001 ppt, preferably between 0.1 ppm to 0.0001 ppt, more preferably between 0.01 ppm to 0.0001 ppt, and most preferably between 1 ppb to 0.0001 ppt and

G. Zinc less than or equal to 3 ppm, preferably less than or equal to 1 ppm to 0.0001 ppt,

in particular between 0.3 ppm to 0.0001 ppt, preferably between 0.1 ppm to 0.0001 ppt, particularly preferably between 0.01 ppm to 0.0001 ppt and very particularly preferably between 1 ppb to 0.0001 ppt. Wherein, for each element, a purity in the range of the detection limit can be sought. Furthermore, the total contamination with the aforementioned

Elements less than 100 ppm by weight, preferably less than 10 ppm by weight, more preferably less than 5 ppm by weight in the sum in the silicon as a direct

Process product of the melt of directional solidification.

As a pure elemental, metallic reducing agent are reducing agent having a content of 99% reducing agent and a maximum of 1% contamination with other metallic compounds and / or other metals. Metallic impurities are iron, manganese, nickel, copper, aluminum, boron, calcium, phosphorus, titanium, zinc. More preferably, the reducing agent has a content of 99.9% reducing agent, particularly preferably 99.99% reducing agent. For production of

Solar grade silicon or semiconductor grade silicon preferably has a content of 99.99% of the reducing agent, more preferably of 99.9999%. Preferably, the elemental, metallic reducing agent has at most a total impurity content of foreign metals of <1 ppm.

A particular advantage of the use according to the invention of silicon tetrachloride, which is obtained as a by-product, in particular in the abovementioned processes, is that the silicon produced in this way directly comprises a technical silicon with a content of at least 96% by weight. Silicon is, in particular, it is pure silicon with a content of 99 wt .-% silicon, preferably high-purity silicon having a content of 99.99 wt .-% silicon, more preferably it is solar grade silicon with a

Content of 99.9999% by weight of silicon or a semiconductor grade silicon containing 99.999999% by weight of silicon. At the same time the content of

Foreign metals, such as sodium, zinc, aluminum, boron, phosphorus, etc. and / or the content of the foreign metal-containing compound, in the solar grade silicon as

Total contamination at less than 100 ppm by weight, preferably less than 10 ppm by weight, more preferably less than 5 ppm by weight.

The foreign metal content and / or the content of the foreign metal-containing compound in the silicon tetrachloride is preferably in relation to the metallic compound, in particular independently, in each case to a content in the range of less than 100 μg kg to the detection limit, in particular of less than 25 μg kg, preferably below 15 μg kg, particularly preferably 0.1 to 10 μg kg are reduced to the respective detection limit. The contents of boron, aluminum, potassium, lithium, sodium, magnesium, calcium, zinc and / or iron are preferably below the stated values. The content of boron and iron in the silicon tetrachloride is particularly preferably below the stated contents. Frequently, the compounds are present dissolved in silicon tetrachloride and can be well separated by means of an adsorbent, such as BCI ₃ .

The foreign metals or foreign metal-containing compounds are generally metal halides, metal hydrogen halides and / or metal hydrides and mixtures of these compounds. But even with organic radicals such as alkyl or aryl groups, functionalized metal halides, metal hydrogen halides or metal hydrides can be removed with very good results from silicon tetrachloride. Examples thereof may be aluminum trichloride or else iron (III) chloride as well as entrained particulate metals, which may originate from continuous processes. In the context of the use according to the invention, it is particularly preferred if the i) the silicon obtained by reduction of metals, in particular

Foreign metals, and / or metal salts, in particular foreign metal salts, whose

If the boiling point is below the melting point of silicon, is purified by melting, in particular complete melting, in particular one or more directional solidification processes follow. The silicon produced by directional solidification preferably has a resistivity between 10 ^"2 and 10 ⁴ ohm.cm.Optically or additionally, ii) the silicon obtained from reduction of metals, in particular foreign metals, and / or metal salts, in particular foreign metal salts, their boiling point above the

Melting point of silicon, by phase separation on cooling,

especially slow cooling, is separated. Phase separation can be used to remove contaminants, foreign metals and foreign metals Compounds are reliably separated from the silicon. Preferably, one or more systems for directional solidification subsequently join. The silicon produced by directional solidification preferably has a specific one

Resistance between 10 ^"2 and 10 ⁴ ohms x cm The aforementioned metals or metal salts, which are separated from the silicon, are considered as foreign metals or

Foreign metal-containing compounds according to the invention.

More preferably, the silicon produced according to the invention has a resistivity between 10 ^"6 and 10 ¹⁰ ohm.cm, in particular, the silicon produced by reduction with the elemental metallic reducing agent has a resistivity between 10 ^{" 5} and 2 x 10 ^"2 ohms x It is preferred if it did not have to be further purified for this resistance value after the reduction, in particular if it originated from one of the abovementioned processes and no significant impurities were introduced by the reducing agent.

The content of silicon or, better, the purity of the silicon with respect to metallic impurities is 99.99 to 99.9999% d. 4n to 6n, preferably from 99.999 to 99.9999999%, d. H. 5n to 9n as high purity silicon. The content of silicon, or better, the purity of silicon with respect to metallic impurities, can be determined by the resistivity of a prepared Si layer or Si-rod. The measurement of the resistivity of silicon can serve to determine the purity of the silicon as well as to indirectly determine the purity of the silicon tetrachloride used.

In particular, the content of impurities by elements of the 3rd main group of the elements of the Periodic Table (so-called p-type impurities) and the 5th main group (so-called n-type impurities) is critical for z. B. semiconductor and solar cell products. The method of determining the resistivity is suitable for detecting and increasing extremely low concentrations of impurities by elements of the 3rd and 5th main groups of the Periodic Table of the Elements quantify, because it is these impurities that influence the resistivity of a silicon layer.

The specific resistance (in short: for specific electrical resistance or resistivity) is a temperature-dependent material constant with the symbol p. The electrical resistance of a conductor with a constant over its length

Cross-sectional area (section perpendicular to the longitudinal axis of a body) is: R = p A l, where R is the electrical resistance, p the resistivity, I the length and A the cross-sectional area of the conductor. Consequently, one can determine p from the measurement of the resistance of a conductor piece of known geometry.

In the context of the present invention, the measurement of the resistance and the layer thickness can take place via the so-called SRP method (spreading resistance probe). For this purpose, a piece of a coated wafer or a sample of Si after

Reduction or directional solidification at a defined angle ground to the substrate. The resistance measurement then takes place by means of two

Sample tips that scan the entire profile at specific intervals and each give a resistance to a specific layer thickness. On the

Beveling angle and the path length can also calculate the layer thickness. The determination of the layer thickness is unnecessary for continuous homogeneous substrates. The method is described in detail in several standards and specifies the procedure described above. The methods used here follow the SEMI standards MF672 and MF674, which are referred to in the MF672. The SEMI standard MF672 is an extension of the SEMI standard MF525. The SEMI standards are also published as ASTM standards (eg ASTM F 672-80). The method for determining the resistivity of silicon can also be found in DE 2010002342.6, the content of which is fully incorporated by reference.

Thus, the method of determining the resistivity provides that the impurities are not directly determined by silicon applied

Methods, but indirectly by measuring a physical property of a silicon obtained according to the invention, wherein the physical property, namely the resistivity is significantly influenced by the concentration of impurities present in the silicon. In particular, contamination by elements of the 3rd and 5th main group of the Periodic Table of the Elements

affect the specific resistance of silicon.

The specific resistance (short for specific electrical resistance or resistivity) is a temperature-dependent material constant with the symbol p. The electrical resistance of a conductor with a constant over its length

Cross-sectional area (section perpendicular to the longitudinal axis of a body) is: R = p A / l, where R is the electrical resistance, p the resistivity, I the length and A the cross-sectional area of the conductor. Consequently, one can determine p from the measurement of the resistance of a conductor piece of known geometry.

To carry out the measurement, it is possible to produce from the silicon obtained according to the invention, if it is not already present as a shaped or specimen, a specimen having defined dimensions, for example by melting, shaping and subsequent solidification. The resistance and the layer thickness are measured by the so-called SRP method (spreading resistance probe). For this purpose, a piece of the specimen is ground at a defined angle. The resistance measurement is then carried out by means of two probe tips, which scan the entire profile at certain intervals and each result in a resistance value to a specific layer thickness. About the bevel angle and the path length can also calculate the layer thickness. The method is described in detail in the standards already mentioned above and specifies the procedure described above.

According to a particularly preferred embodiment, the use of the silicon tetrachloride by-products in a large-scale process, d. h. the silicon tetrachloride is reacted with an elemental, metallic reducing agent to silicon and metal chlorides in a large-scale process.

Preferably followed by directional solidification to reduce the

Foreign metal content and any existing silicon oxides and

Silicon carbide in silicon. As a large-scale process is a conversion of Silium tetrachloride <50 kg / hour with a metallic reducing agent,

in particular> 100 kg / hour, particularly preferably> 500 kg / hour.

The invention also relates to the use of the resulting metal chlorides, which can be supplied for commercial use and so to

Profitability of the inventive use of silicon tetrachloride by-products contribute. The use of the sodium chloride obtained as a road salt is particularly noteworthy, since it is obtained inexpensively as a product in the process and process-related has a particularly low impurity profile.

In addition, climate change has occurred in the recent past

long-lasting winters with lots of snow and ice multiple times to a shortage of road salt. The shortage can be remedied in an economical manner with a high quality product due to the use of the invention. Furthermore, the i) sodium chloride obtained by the use according to the invention can be used: as table salt (according to the definition of the regulations for food, for example table salt may contain only 1% colloidal silica, max 20 ppm

Hexacyanoferrate), pickling salt; with iron oxide in animal husbandry; as road salt,

Industrial salt, in particular with colored marking as road salt, for the preparation of cold mixes, for salting out soaps, for use as pit salt; for water treatment, for the preservation of hides, for the preparation of inhalation solutions, for

Production of mineral waters, as emetics, for weed control, for

Production of single crystals, for the production of optical lenses, windows, prisms, in the Solvay process for the reaction with calcium carbonate to sodium carbonate; as starting material, d. H. as feedstock for the melt flow electrolysis for the production of sodium, as educt for the chlor-alkali electrolysis for the production of chlorine and

Caustic soda, and / or ii) the zinc chloride can be used: for the preparation of salt baths in the production of polyacrylic fibers, as an electrolyte in

High power cells (Leclanche elements); soldering fluid; Lewis acid, in particular as Lewis acid for dehydration and / or condensation in organic

synthesis; in refining in oil processing; for galvanizing, tinning, dulling metals; in the production of activated carbon, as preservative and hygroscopic additive for sizing and finishing liquors, for reserving sulfur and vat dyes, as stabilizer for

diazonium; in the production of dyes; for the manufacture of paper mache and vulcanized fiber, for the production of medical wash waters, caustics or pastes, in particular for the treatment of infected wounds and ulcers; as a disinfectant; for the preparation of emulsions for use in photography, for the production of copy paper; as a staining reagent in the

Thin-layer or paper chromatography and / or for the production of zinc carbonate. Furthermore, both the sodium chloride and the zinc chloride can be converted by means of electrolysis in sodium or zinc and chlorine and the inventive

Use to be fed again.

General Application Example A by-pass stream from the known Siemens process for the production of pure Si from TCS containing STC and traces of TCS, hexachlorodisilane, pentachlorodisilane and tetrachlorodisilane was used in a reactor with metallic sodium

(Purity 99.8%) to metallic Si and NaCl reacted. After phase separation, the resulting silicon was subjected to double directional solidification. The silicon thus obtained had a purity of 5 N (99.999%) and is suitable for solar applications. The resulting sodium chloride was readily available

Treatment has a purity of 99.1% and is therefore suitable for technical applications.

Claims

claims

1 . Use of silicon tetrachloride as a by-product in the preparation of Siliciunn, monosilane or halosilanes as a by-product, for the production of Siliciunn,

characterized,

that the silicon tetrachloride with an elemental, metallic

Reductant is converted to silicon and metal chlorides.

2. Use according to claim 1,

characterized,

that the silicon tetrachloride, which is by-produced in the production of

Silicon, monosilane or halosilanes obtained is reacted without further purification with an elemental, metallic reducing agent.

3. Use according to one of claims 1 or 2,

characterized,

in that as elemental, metallic reducing agent an alkali metal, an element of the 2nd subgroup of the periodic table or a mixture containing at least one of the elements is used.

4. Use according to one of claims 1 to 3,

characterized,

that the silicon tetrachloride

i) by-product of the Siemens process, in which silicon from Tnchlorsilan in

Presence of hydrogen is formed;

ii) a by-product of the production of silicon-based tochlorosilane with hydrogen chloride;

iii) is a by-product of dismutation reactions in the preparation of monosilane, monochlorosilane, dichlorosilane, tochlorosilane and / or polyhalosilanes.

5. Use according to one of claims 1 to 4,

characterized,

that sodium or zinc is used as the reducing agent.

6. Use according to one of claims 1 to 5,

characterized,

that the silicon produced is technical silicon with a content of 96% by weight of silicon, in particular it is pure silicon with a content of 99% by weight of silicon, preferably high-purity silicon with a content of 99.99% by weight

Silicon, particularly preferably it is solar grade silicon containing

99.9999% by weight of silicon or a semiconductor grade silicon containing 99.999999% by weight of silicon.

7. Use according to one of claims 1 to 6,

characterized,

that the silicon produced ^{"having 6} to 10 ¹⁰ ohm x cm, and in particular, the silicon produced by reduction to the elemental metallic reducing agent, a specific resistance between ^10" a resistivity of between 10 ⁵ and 2 x 10 ^"2 ohm x cm.

8. Use according to one of claims 1 to 6,

characterized,

that the silicon tetrachloride is reacted with an elemental, metallic reducing agent to silicon and metal chlorides in a large-scale process, in particular with a conversion of> 50 kg / hour, preferably> 100 kg / hour, more preferably> 500 kg / hour.

9. Use according to one of claims 1 to 8,

characterized,

that metallic impurities in the silicon tetrachloride by means of filtration, liquid impurities by means of an adsorbent, dissolved impurities by means of an adsorbent or impurities by means of a combination the above measures are separated before the reaction with the reducing agent.

10. Use according to claim 1,

characterized,

that the silicon tetrachloride, which is obtained as a by-product in the production of silicon, monosilane or halosilanes, from metallic

Impurities in the silicon triethrachloride by filtration, from liquid

Impurities by contacting with an adsorbent, dissolved impurities by contacting with an adsorbent, or impurities by a combination of the foregoing

Measures are removed before the reaction with the reducing agent and the silicon tetrachloride thus treated is then reacted with an elemental, metallic reducing agent.

1 1. Use according to one of claims 1 to 10,

characterized,

that i) the silicon obtained from reduction of metals and / or

Metal salts whose boiling point is below the melting point of silicon, is purified by melting, in particular one or more directional solidification processes,

ii) the silicon obtained by reduction of metals and / or metal salts whose boiling point is above the melting point of silicon

Phase separation is separated during cooling, in particular one or more directional solidification processes follow.

12. Use according to claim 1 1,

characterized,

the silicon obtained by reduction after directional solidification has a resistivity between 10 ^"2 and 10 ⁴ ohm.cm.

13. Use according to one of claims 1 to 12,

characterized,

that as metal chlorides sodium chloride and / or zinc chloride are obtained.

14. Use according to one of claims 1 to 13,

characterized,

that

i) the sodium chloride is used as table salt, pickling salt; with iron oxide in animal husbandry; as road salt, industrial salt, in particular with colored

Marking as road salt, for the production of cold mixes, mine salt; to

Water treatment, for the preservation of hides, for the manufacture of

Inhalation solutions, for the production of mineral waters, as an emetic, for weed control, in the Solvay process for the reaction with calcium carbonate to sodium carbonate; as educt for the melt flow electrolysis for the production of sodium, as starting material for the chlor-alkali electrolysis for the production of chlorine and caustic soda, and

ii) the zinc chloride is used for the preparation of salt baths in the

Production of polyacrylic fibers, as electrolyte in high-performance cells (Leclanche elements); soldering fluid; Lewis acid, especially as Lewis acid for

Dehydration and / or condensation in organic syntheses; in the

Refining in oil processing; for galvanizing, tinning, dulling metals; in the production of activated carbon, as a preservative and hygroscopic additive in sizing and finishing liquors, for reserving sulfur and vat dyes, as a stabilizer for

diazonium; in the production of dyes, for the production of Papiermache and vulcanized fiber, for the production of medical wash water, caustics or pastes, in particular for the treatment of wounds and

ulcers; as a disinfectant; for the preparation of emulsions for use in photography, for the production of copy paper; when

Staining reagent in thin-layer or paper chromatography and / or zur

Production of zinc carbonate.

15. The use of the by-product silicon tetrachloride according to any one of claims 1 to 11 for the production of high-purity silicon comprising reduction with an elemental metallic reducing agent, the silicon having the following impurity profile,

a) aluminum less than or equal to 5 ppm, preferably between 5 ppm and 0.0001 ppt, b) calcium less than or equal to 2 ppm, preferably between 2 ppm and 0.0001 ppt, c) iron less than or equal to 20 ppm, preferably between 10 ppm and zero , 0001 ppt, d) nickel less than or equal to 10 ppm, preferably between 5 ppm and 0.0001 ppt, e) phosphorus less than 10 ppm to 0.0001 ppt,

f) Titanium less than or equal to 2 ppm, preferably less than or equal to 1 ppm to 0.0001 ppt, g) Zinc less than or equal to 3 ppm, preferably less than or equal to 1 ppm to 0.0001 ppt.