EP2989146A1

EP2989146A1 - Method and device for producing polychlorosilanes

Info

Publication number: EP2989146A1
Application number: EP14707771.3A
Authority: EP
Inventors: Jürgen Erwin LANG; Hartwig Rauleder; Ekkehard MÜH; Imad Moussallem
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2013-04-24
Filing date: 2014-03-04
Publication date: 2016-03-02
Also published as: WO2014173573A1; DE102013207444A1; KR101760592B1; KR20160002832A; US9994456B2; MY171203A; CN105121516A; US20160039681A1; CN105121516B; JP2016516665A; TWI582045B; JP6385425B2; TW201504142A

Abstract

The invention relates to a method and a device for producing polychlorosilanes from monomeric chlorosilanes by exposing the chlorosilanes to a thermal plasma.

Description

Process and apparatus for the production of polychlorosilanes

The invention relates to a method and an apparatus for the production of polychlorosilanes from chlorosilanes by exposing monomeric chlorosilane to a thermal plasma.

From the prior art, a number of methods for the preparation of

Polychlorosilanes known. Thus, DE 10 2006 034 061 discloses a reaction of

Silicon tetrachloride with hydrogen for the production of polysilanes. Due to the reaction in the presence of hydrogen, the polysilanes produced are hydrogen-containing. In order to keep the plant in continuous operation, tetrachlorosilane is added in excess relative to the hydrogen. In addition, the disclosed equipment has a complex structure and allows only the production of polysilane mixtures. An increased molecular weight of the polysilanes can only by connecting several reactors and

High frequency generator can be achieved. After each passing through the

one after the other, the molecular weight of the polysilanes increases after each plasma reactor. The disclosed process is limited to the preparation of non-degradable gas-phase compounds.

EP 1 264 798 A1 discloses a process for working up by-products containing hexachlorodisilane in the production of polycrystalline silicon.

US Pat. Nos. 4,542,002 and WO 2009/143823 A2 also disclose plasma-chemical processes for the preparation of polychlorosilanes starting from silicon tetrachloride and hydrogen.

As a result of production, hydrogen-containing polychlorosilanes are obtained. According to WO 2009/143823 A2, mixtures of hydrogen-containing high molecular weight polychlorosilanes are obtained. The silicon tetrachloride contained in the polychlorosilanes must be removed by distillation before further use in a vacuum. Particularly disadvantageous in the prior art is the need to prepare the polychlorosilanes in the presence of gaseous hydrogen. As a result, very high security measures are taken on the materials and the security of the system.

The object of the present invention is to provide an economical process for the preparation of polychlorosilanes, in particular of polyperchlorosilanes, which is distinguished by a high yield and a particularly high purity of the products of the process. A Another task was to be able to dispense with the use of hydrogen for the production of polychlorosilanes. Likewise, polychlorosilanes should also be able to be prepared without the requirement that they must be converted into the gas phase without decomposition during their production. Another requirement was to produce the polychlorosilane immediately substantially free of monomeric chlorosilanes. An additional object was to provide a low cost, easily constructed and easy to use plant for the production of polychlorosilanes. A particular focus has been to minimize the internal surfaces that can contribute to the contamination of the polychlorosilanes. In addition, the system should require little space vertically. In particular, it should also be possible to produce high-purity, high molecular weight polychlorosilanes which do not have to be purified before further processing, such as for the deposition of silicon. A further object was to provide a process for producing highly pure, high molecular weight polychlorosilanes and to provide the polychlorosilanes, without these polychlorosilanes having to be converted into the gas phase without decomposition for purification, for example, before they have to be distilled.

The objects are achieved by a method according to claim 1, the polychlorosilanes available thereafter according to claim 15 and by the system according to claim 12. Surprisingly, it has been found that chlorosilanes, comprising monomeric chlorosilanes, optionally in admixture with polychlorosilanes, in thermal plasma, ie a plasma in thermal equilibrium, to polychlorosilanes, in good yield,

According to the invention can be reacted to Polyperchlorsilanen, in particular to

Mixtures comprising hexachlorodisilane, octachlorotrisilane, decachlorotetrasilane,

Dodecachloropentasilan and / or mixtures containing at least two of the mentioned

Links. Preference is given to polyperchlorosilane mixtures comprising polyperchlorosilanes having 2 to 8 silicon atoms. Also preferred is the preparation of higher molecular weight polychlorosilanes having at least three silicon atoms, in particular having 3 to 8 silicon atoms. It was particularly surprising that the polychlorosilanes could be prepared from monomeric chlorosilanes, preferably from tetrachlorosilane, as well as from tetrachlorosilane, trichlorosilane and / or dichlorosilane substantially without the presence of hydrogen gas in the thermal plasma. The particular economic advantage of the method according to the invention is in particular by the device according to the invention, with a

Gas discharge reactor, which is arranged between two columns achieved. The device according to the invention comprises a plasma reactor, ie a

Gas discharge reactor, with two associated reactive distillation columns. Preferably, one of the columns and the gas discharge reactor is a recycle to the renewed

Assigned by passage of unreacted monomeric chlorosilanes through the gas discharge reactor, the figure 3 shows schematically. The inventively produced

Polychlorosilanes, in particular polyperchlorosilanes, are preferably free of hydrogen.

In the context of the invention, a Polychlorsilan deemed to be free of hydrogen, if it is ^"located ° wt .-%, in particular less than 1 ^x10" a content of hydrogen atoms of less than 1 x10 ⁴ wt .-%, more preferably less than 1 x10 ^"6 wt. -% up to the detection limit currently 1 x ^{10 "10} wt .-%.

The invention also relates to polychlorosilanes with a content of

Hydrogen atoms of less than 1 x 10 ^" ° wt .-%, preferably less than 1 x 10 ^{" 4} wt .-% up to the aforementioned detection limit. The preferred method for determining the content of hydrogen atoms is ¹ H NMR spectroscopy.

Polychlorosilanes according to the invention comprise the homologous series of

Polyperchlorosilanes of the general formula II,

II Si _n Cl 2n + 2,

with n greater than or equal to 2, which forms linear and / or branched chains, and the

Polyperchlorosilanes which form rings or polymers, where the polymers can also be branched and / or cyclic, with the idealized formula III,

IN Si _n CI ₂ n,

with n greater than or equal to 3, as well as the silicon chlorides with a lower chlorine content of the idealized formula IV,

IV SiC _{, 5} .

Particularly preferred as polychlorosilanes are compounds of the general formula II Si _n Cl 2n + 2, where n is greater than or equal to 2, in particular greater than or equal to 2 to 100, preferably n greater than or equal to 2 to 50, preferably in each case independently n greater than or equal to 2, 3 , 4, 5, 6, 7, 8, 9 or 10, preferably 2 to 8, more preferably with n equal to 2 or 3, wherein they can form linear as well as branched chains; and compounds of general formula III, the rings or polymers form with Si _n Cl2n, with n is greater than or equal to 3, in particular with n greater than or equal to 4 to 100, in particular with n greater than or equal to 4 to 50, particularly preferably in each case independently with n greater than or equal to 4 , 5, 6, 7, 8, 9 or 10, as well as lower chlorine content polychlorosilanes according to the general formula IV with Si _n Cli _{, 5n} , with n greater than or equal to 4 or 5, in particular with n greater than or equal to 6 to 200, preferably with n greater than or equal to 8 to 100. A particularly great advantage of the method according to the invention is that these polychlorosilanes can be used as a single compound or in a mixture without further purification for the deposition of high-purity silicon layers with solar grade silicon or semiconductor quality. According to the invention this polychlorosilanes are substantially free of hydrogen, in particular is their content of hydrogen atoms below 1 x10 ^"° wt .-%, in particular less than 1 ^{x10" 4} wt .-%, more preferably less than 1x10 ^"6 wt .-% up to the detection limit of 1 x ¹⁰ -10% by weight. The polychlorosilanes obtained according to the invention are thus free of hydrogen atoms. The invention thus provides a process for the preparation of polychlorosilanes, and also polychlorosilanes obtainable by this process, in particular polyperchlorosilanes, in which chlorosilanes comprising at least one monomeric chlorosilane of the general formula I,

IH _x SiCl4-x, where x is independently selected from 0, 1, 2 or 3. Preferably, x is 0, 1 or 2, more preferably x is 0 or 1, more preferably x is 0, or a mixture comprising at least two monomeric chlorosilanes of the formula I, in particular selected from tetrachlorosilane, trichlorosilane and dichlorosilane, preferably pure tetrachlorosilane or pure tetrachlorosilane with a content of trichlorosilane and / or dichlorosilane of less than or equal to 20 wt .-% in the mixture, and optionally chlorosilanes in the mixture with a low content of hexachlorodisilane, exposed to a thermal plasma and converted to polychlorosilanes.

The particular advantage of the method is that no hydrogen carrier gas and no additional catalyst must be used. Thus, in the process, monomeric

Chlorosilanes of the general formula I or mixtures of monomeric chlorosilanes of the formula I are reacted in the thermal plasma to polychlorosilanes, wherein substantially no additional hydrogen-containing compounds, in particular hydrogen, must be added. Chlorosilanes are monomeric chlorosilanes and optionally polychlorosilanes, such as preferably hexachlorodisilane. The polychlorosilanes are prepared only by reacting monomeric chlorosilanes of the general formula I in the presence of a thermal plasma, in particular in the thermal plasma. Preferably, a defined reflux ratio of monomeric chlorosilanes of the general formula I, which are considered to be low boilers, on a condenser of the

adjusted device according to the invention.

It may also be advantageous to withdraw from the system only forming monochlorosilane, HCl and / or monosilane at the top of the low-boiling column of the device.

All other monomeric chlorosilanes are condensed and recycled to the system. This separation is easily possible by means of a corresponding temperature of the capacitor. According to a particularly preferred procedure, in the case of tetrachlorosilane as starting material with a certain content of trichlorosilane and / or dichlorosilane, the hexachlorodisilane formed is condensed and discharged from the condenser, while the further chlorosilanes are fed again in gaseous form to the gas discharge reactor.

The possible reactions in the thermal plasma can be ideally represented as follows: n H _x SiCl ₄ - _x tnerm ^! scnes nasma Si _n CI ₂ n ₊₂ + other process products, such as HCl and H ₂ , where x = 0, 1, 2 or 3, preferably with x equal to 1 or 0, independently preferably with n = 2 or 3.

2 HSiCIs + 2 SlCI ₄ thermal plasma ₂ g. ^ _{+ 2 HC |}

3 HSiCi's thermal plasma SI ₃ CI ₇ H + 2 HCl H ₂ SiCl ₂ + 2 SlCI ₄ thermal plasma ^ g. ^ _{+ 2 HC |}

4 HSiCIs + 3 SlCI ₄ thermal plasma ^, ^ ₊ g. ^ _{+ H3} g _iC | _{+ HC |} As chlorosilanes of the general formula I, preference is given to using tetrachlorosilane, trichlorosilane, dichlorosilane or mixtures thereof. A particular advantage of the process is the possibility of producing polychlorosilanes of semiconductor quality starting from ultrapure tetrachlorosilane (STC _eg ).

In the context of the invention, the term "electronic grade", abbreviated "eg", is used for "highly pure".

Alternatively, polychlorosilane can be prepared starting from ultrapure trichlorosilane (TCS _eg ), or from ultrapure dichlorosilane (DCS _eg ), as well as from mixtures of said chlorosilanes. A preferred correspondingly high-purity mixture comprises tetrachlorosilane containing trichlorosilane and / or dichlorosilane.

For the preparation of polychlorosilanes according to the invention is a high to high purity monomeric chlorosilane of the general formula I or a mixture of the monomers

Chlorosilanes of the formula I used, such as ultrahigh tetrachlorosilane, ultrahigh trichlorosilane and / or highly pure dichlorosilane, preferably having a content of chlorosilanes of 80 to 99.9999999 wt .-%, ad 100 wt .-% Polychlorosilanes. Here, in the high-purity chlorosilane, the total impurity in the range of 100 ppm by weight to 0.001 ppm by weight, and at

very pure chlorosilane of from 50 ppm by weight to 0.001% by weight, preferably from 40 ppm by weight to 0.001% by weight of ppt.

This total impurity has the following elements a to i. The content of monomeric chlorosilanes is preferably 98% by weight to 99.9999999

Wt .-%, with less than or equal to 100 wt .-% to 0.001 wt ppt total impurities in a high purity chlorosilane, preferably less than 50 ppm by weight to 0.001 wt ppt in a high purity chlorosilane, and optionally ad 100

% By weight of polychlorosilanes, the total impurities of the monomeric chlorosilanes of the general formula I having elements as follows: a. Aluminum from 15 ppm by weight to 0.0001 ppm by weight, and / or

b. Boron from 5 to 0.0001 parts by weight,

preferably in the range from 3 ppm by weight to 0.0001 ppm by weight, and / or c. Calcium less than 2 ppm by weight,

preferably from 2 ppm by weight to 0.0001 ppm by weight, and / or

d. Iron from 5 ppm by weight to 0.0001 ppm by weight,

preferably from 0.6 ppm by weight to 0.0001 ppm by weight, and / or

e. Nickel from 5 ppm by weight to 0.0001 ppm by weight,

preferably from 0.5 ppm by weight to 0.0001 ppm by weight, and / or

f. Phosphorus from 5 ppm by weight to 0.0001 ppm by weight,

preferably from 3 ppm by weight to 0.0001 ppm by weight, and / or

H. Titanium less than 10 ppm by weight,

preferably less than or equal to 2 ppm by weight,

furthermore preferably from 1 ppm by weight to 0.0001 ppm by weight,

more preferably from 0.6 ppm by weight to 0.0001 ppm by weight,

more preferably from 0.1 ppm by weight to 0.0001 ppm by weight, and / or

H. Zinc less than or equal to 3 ppm by weight,

preferably from 1 ppm by weight to 0.0001 ppm by weight,

furthermore preferably from 0.3 ppm by weight to 0.0001 ppm by weight, and / or

i. Carbon,

wherein for carbon a concentration in the range of known to the expert of the measuring method dependent detection limit is sought.

The determination of the total contamination with the aforementioned elements is preferably carried out by means of ICP-MS.

A particular advantage of the process according to the invention is that the preparation of the polysilanes can be selectively controlled. Are preferred by the method as

Polychlorosilane Polyperchlorsilane obtained with 2 to 8 silicon atoms, are preferred

Polychlorosilanes having 2, 3, 4, 5, 6 and / or 7 silicon atoms, preferably of the formulas II, II and / or IV, which are free from hydrogen within the limits of detection known in mass spectroscopy. Particularly preferred polychlorosilanes include hexachlorodisilane, octachlorotrisilane, n-

Decachlorotetrasilane, / ^' so-decachlorotetrasilane, ie f-decachlorotetra-silane, dodecachloropentasilane as n-dodecachloropentasilane, 2-trichlorosilyl-decachlorotetrasilane, 1,1-di (trichlorosilyl) octachlorotrisilane, 2,2-di (trichlorosilyl) octachlorotrisilane and / or 1,2-di (trichlorosilyl) - octachlorotrisilane as a single compound or in a mixture comprising at least two of said polychlorosilanes.

A further advantage of the process is the production of ultrahigh-purity polychlorosilanes, such as very pure octachlorotrisilane or very pure hexachlorodisilane, and ultrahighly defined decahlorotetrasilanes and / or dodecachloropentasilanes, which are known from US Pat

Requirements of the semiconductor industry are sufficient.

Thus, according to a particularly preferred variant of the method, ultrachloroacetic octachlorotrisilane with octachlorotrisilane content of 95.9999% by weight to 99.999999% by weight is isolated as polychlorosilane, the remaining content being up to 99.999999% by weight in each case

Hexachlorodisilane, decachlorotetrasilane and / or dodecachloropentasilane. According to one alternative, the polychlorosilane used is ultrahigh-purity hexachlorodisilane containing

Hexachlorodisilane of 95.9999 wt .-% to 99.999999 wt .-% isolated, the remaining content to 99, 999999 wt .-% each Octachlortrisilan, Decachlortetrasilan and / or

Dodecachloropentasilan includes. The content of hydrogen in the aforementioned

Polychlorosilanes are preferably below the detection limit. As an analysis, known in the art, such as CHN analysis, ¹ H-NMR, preferably in combination with ICP-MS.

According to a particularly preferred variant of the method, highly pure octachlorotrisilane, ultraprecious decachlorotetrasilane or ultrapure dodecachloropentasilane or a mixture of polychlorosilanes are isolated as polychlorosilane, ultrapure polychlorosilanes as ultrahigh hexachlorodisilane, in each case having a titanium content of less than 10 ppm by weight, preferably less than 8

Ppm by weight, particularly preferably less than 5 ppm by weight, more preferably less than 1 ppm by weight (measured by means of ICP-MS).

As hochstreine Polychlorosilanes, preferably hochstreine Polyperchlorsilane, in particular ultrahigh-hexachlorodisilane, ultrahigh-octachlorotrisilane, hochreckines Decachlortetrasilan or hochstreines dodecachloropentasilane, preferably as the ultrahigh mixture of

Polychlorosilanes mentioned above are polychlorosilanes having a content of polychlorosilane, preferably of polyperchlorosilane, of 99.99 to 99.9999999% by weight, preferably of 99.9999 to 99.9999999% by weight, the total impurity being below 100 ppm by weight . in particular with impurities of one, several or all elements selected from boron, phosphorus, carbon and foreign metals, as well as hydrogen, preferably selected from boron, phosphorus, carbon, aluminum, calcium, iron, nickel, titanium and zinc and / or hydrogen.

More preferably, the polychlorosilane obtained in the process according to the invention is a polyperchlosilane, preferably a highly pure polyperchlorosilane having a total impurity concentration of less than or equal to 100 ppm by weight up to the detection limit or up to 0.001% by weight of the definition below. More preferably, a high purity polychlorosilane is obtained with from 50 ppm by weight to 0.001% by weight of total impurities.

Particularly preferred is a polychlorosilane, abbreviated PCS, obtained, in particular

Hexachlorodisilane, octachlorotrisilane or a mixture comprising hexachlorodisilane,

Octachlorotrisilane, decachlorotetrasilane and / or dodecachloropentasilane, preferably highly to hochstreines Polychlorosilane having 2 to 8, preferably having 2 to 7 silicon atoms, further preferably having 3 to 8 silicon atoms, preferably polyperchlorosilanes, wherein the

Polychlorosilane, in particular a content of octachlorotrisilane from 20 to 99.9999 wt .-%, preferably in a mixture with other polychlorosilanes, more preferably containing octachlorotrisilane from 91 to 99.9999999 wt .-%, more preferably with a Content of 99.99 to 99.9999999 wt .-%.

It is also possible to obtain a high to very high purity hexachlorodisilane which may be present in a mixture with other polychlorosilanes, preferably polyperchlorosilanes. Particularly preferred is a hexachlorodisilane having a content of 20 to 99.9999 wt .-%, preferably with a content of 91 to 99.9999999 wt .-%, more preferably with a content of 99.99 to 99.9999999 wt. %, wherein the aforementioned polysilanes each independently have the following impurity profile of one, several or all of the following elements. As highly pure polychlorosilanes be in the invention polychlorosilanes with

Impurities in the following concentrations: a aluminum less than 5 ppm by weight,

preferably from 5 ppm by weight to 0.0001 ppm by weight, furthermore preferably from 3 ppm by weight to 0.0001 ppm by weight, and / or

b. Boron from 10 ppm by weight to 0.0001 ppm by weight,

preferably in the range of 5 to 0.0001 parts by weight,

furthermore preferably in the range from 3 ppm by weight to 0.0001 ppm by weight, and / or

c. Calcium less than 2 ppm by weight,

preferably from 2 ppm by weight to 0.0001 ppm by weight, and / or

d. Iron less than or equal to 20 ppm by weight,

preferably from 10 ppm by weight to 0.0001 ppm by weight,

further preferably from 0.6 ppm by weight to 0.0001 ppm by weight, and / or

e. Nickel less than or equal to 10 ppm by weight,

preferably from 5 ppm by weight to 0.0001 ppm by weight,

further preferably from 0.5 ppm by weight to 0.0001 ppm by weight, and / or

f. Phosphorus from 10 ppm by weight to 0.0001 ppm by weight,

preferably from 5 ppm by weight to 0.0001 ppm by weight,

further preferably from 3 ppm by weight to 0.0001 ppm by weight, and / or

G. Titanium less than 10 ppm by weight,

preferably less than or equal to 2 ppm by weight,

more preferably from 1 ppm by weight to 0.0001 ppm by weight,

furthermore preferably from 0.6 ppm by weight to 0.0001 ppm by weight,

particularly preferably from 0.1 ppm by weight to 0.0001 ppm by weight, and / or

H. Zinc less than or equal to 3 ppm by weight,

preferably from 1 ppm by weight to 0.0001 ppm by weight,

further preferably from 0.3 ppm by weight to 0.0001 ppm by weight, and / or

i. Carbon, and / or

j. Hydrogen,

with carbon and hydrogen each having a concentration in the range of

It is the intention of a person skilled in the art which depends on the measuring method of the detection limit.

As stated, the total contamination of the polychlorosilane with the abovementioned elements or impurities is from 100 ppm by weight to 0.001% by weight in highly pure

Polychlorosilane, preferably from 50 ppm by weight to 0.001% by weight in ultrapure polychlorosilane, more preferably from 10 ppm by weight to 0.001% by weight, particularly preferably from 5 ppm by weight to 0.001% by weight in the Total. The process can be monitored continuously by means of online analytics known to those skilled in the art. The required purity can be determined by means of GC, IR, NMR, ICP-MS or by resistance measurement or GD-MS after deposition of Si are checked.

Another advantage of the method is that it can be dispensed with the addition of expensive noble or inert gases. Alternatively, a drag gas, preferably a pressurized inert gas such as nitrogen, argon, another noble gas, or mixtures thereof may be added.

According to a further preferred process variant, the process of the invention is used for the preparation of polychlorosilanes, in particular Polychlorsilangemischen comprising hexachlorodisilane, octachlorotrisilane, Decachlortetrasilan and / or dodecachloropentasilane, optionally in admixture with higher molecular weight polychlorosilanes having six to seven silicon atoms, by monomeric chlorosilane of the general formula I, in particular

Tetrachlorosilane, trichlorosilane, dichlorosilane or a mixture of monomeric chlorosilanes of the formula I containing two of said compounds or all three compounds are exposed in a device comprising a gas discharge reactor with two columns of a thermal plasma.

Further, it is preferred if chlorosilane of the formula I of a column to remove the

Polychlorosilane, which is arranged upstream of the gas discharge reactor, is fed or is introduced directly into the gas discharge reactor. The severed

Polychlorosilanes are considered high boilers. The ratio of higher molecular weight polychlorosilanes having six to eight silicon atoms to low molecular weight polychlorosilanes having two to five silicon atoms can be determined in the process according to the invention via the contact times in the

Gas discharge reactor can be easily controlled by the flow rate.

According to a particularly preferred embodiment, the process is carried out in a device comprising a first column with a column inlet for separating the

Polychlorosilane upstream, in particular below the gas discharge reactor and a second column having a column inlet for the separation of the low boilers, in particular the monomeric chlorosilanes, and optionally entrained high boilers, such as

Polychlorosilanes, downstream behind, in particular above the gas discharge reactor. The column outlet of the second column is preferably assigned a condenser for condensing the low boilers. The device can also be used as a plasma Reaktivdestillationsvorrichtung be designated, wherein the plasma reactor is arranged between two reactive distillation columns.

Preferably, optionally discharged polychlorosilanes, such as hexachlorodisilane, are condensed on the abovementioned capacitor. Further, the capacitor is associated with a return, the low boilers and optionally co-condensed Polychlorsilane the first column, in particular in the upper half, preferably in the upper third, or the

Gas discharge reactor feeds again.

The polychlorosilanes can run into the bottom draw in the first column, or if necessary

partially or completely, depending on the desired Polychlorsilanprodukt, condensed and fed to a receiving vessel at the bottom offtake or a bottom evaporator. The

The temperature of the bottom evaporator is adjusted so that the desired polychlorosilane is not converted into the gas phase. As a bottom evaporator may be preferred

Circulating evaporator for gentle heating of the polysilanes are used. Alternatively, bottom product can also be continuously discharged in order to minimize the thermal load.

The recovered polychlorosilane can be further purified as needed, for example, distilled or purified by chromatography. However, further purification is generally not necessary for polychlorosilanes prepared according to the invention. If desired, the polychlorosilane obtained may be subjected to vacuum distillation, in particular to adjust the content of a specific polychlorosilane, if mixtures of polychlorosilanes have been obtained. Thus, an Octachlortrisilan or Decachlortetrasilan containing preferably

Polychlorosilane be distilled in vacuo to increase the content of the desired Polychlorsilans. Alternatively or additionally, a chromatographic work-up can also be followed in order to remove impurities or else to adjust the content of octachlorotrisilane or, for example, to decachlorotetrasilane in polychlorosilane.

If polychlorosilanes having 3 to 7 silicon atoms are desired as polychlorosilanes, the condensed low-boiling components comprising monomeric chlorosilanes and in particular hexachlorodisilane are passed as low-boiling components through the second column and condensed on the condenser as low-boiling components and recycled to the first column or into the first column

Gas discharge reactor returned. In the first column, the temperature control is set to a value which permits the separation of substantially high purity polychlorosilanes, in particular allowed with at least 2 silicon atoms at the column exit of the first column.

The polychlorosilanes include in particular polyperchlorosilane mixtures comprising

Polyperchlorosilanes having 2 to 8 silicon atoms, preferably octachlorotrisilane,

Decachlorotetrasilane and / or dodecachloropentasilane, or polyperchlorosilanes with 6 and 7 silicon atoms, which can run at the column outlet of the first column in the bottom. In this way, the desired polychlorosilanes can pass through the first column and be separated without first being converted to the gas phase.

According to a further process variant, the (i) the gas discharge reactor leaving the second column chlorosilanes of formula I in admixture with hexachlorodisilane in the device (0) on the condenser (5) of hexachlorodisilane are separated. For example, only hexachlorodisilane is condensed and discharged, the monomeric chlorosilanes remain in the gas phase and are recycled, (ii) via the recycling, the chlorosilanes of formula I are recycled to the first column and, (iii) passed through the gas discharge reactor again, and (iv ) Polychlorosilanes, especially ultrahigh polyperchlorosilanes comprising octachlorotrisilane, decachlorotetrasilane and / or dodecachloropentasilane, on

Column exit of the first column obtained, in particular as Polyperchlorsilangemisch comprising Polyperchlorsilane having 2 to 8 silicon atoms, in particular with 3 to 8

Silicon atoms.

According to a further process variant, the (i) the gas discharge reactor leaving the second column chlorosilanes of formula I in mixture with hexachlorodisilane in the device (0) on the capacitor (5) of hexachlorodisilane are separated, for example, only hexachlorodisilane is condensed and discharged, the monomeric Chlorosilanes remain in the gaseous phase and are recycled, (ii) via the recycling, the chlorosilanes of formula I are again passed through the gas discharge reactor, and (iii) polychlorosilanes are recovered at the column exit of the first column.

Additionally or alternatively to one of the aforementioned features are preferred

Polychlorsilangemische obtained having at least 1 mol% of branched polychlorosilanes in the overall composition, preferably the proportion is greater than or equal

1.5 mol%. Further, a method is preferred by chlorosilane of the general formula I or a mixture of chlorosilanes of formula I and optionally chlorosilane mixed with hexachlorodisilane is introduced into the gas discharge reactor or the first column is fed, preferably the chlorosilane or a mixture is gaseous in the

Gas discharge reactor or the first column supplied. In this case, it is further preferred if the chlorosilane is evaporated on first supply, in a recirculation as low boilers, the chlorosilane is evaporated in the first column, while formed octachlorotrisilane and / or if desired hexachlorodisilane are not evaporated and in the

Reservoir can drain at the bottom and collected.

The monomeric chlorosilanes are considered low boilers, the polychlorosilanes are considered high boilers, with the exception in a production of Polychlorsilanen with 3 to 8 silicon atoms. In this special case hexachlorodisilane is also considered to be condensed in the condenser low boilers. In all other manufacturing variants hexachlorodisilane is considered high boilers and should run in the first column in the template. In the process according to the invention, optionally formed hydrogen and / or hydrogen chloride are discharged as process gases from the process and can subsequently be separated, condensed outside this device or fed to another process.

It is likewise preferred if in the method according to the invention

(i) condensing the gas discharge reactor via the second column leaving chlorosilane of the formula I, in particular tetrachlorosilane, trichlorosilane and / or dichlorosilane and / or mixtures thereof, and polychlorosilanes, in particular comprising hexachlorodisilane and optionally also octachlorotrisilane, condensed in the apparatus on the capacitor and (ii (iii) this chlorosilane is optionally passed through the gas discharge reactor in admixture with hexachlorodisilane and / or octachlorotrisilane, while (iv) polychlorosilanes having preferably 4 to 8 silicon atoms on the

Column exit of the first column are obtained, in particular the

Polychlorosilane (v) obtained in a, the column output associated with the original container or a column outlet associated bottom evaporator. The thus obtained

Polychlorosilane is high to highest purity according to the above definition.

With respect to the formation of higher molecular weight polychlorosilanes, the process is not limited, so that on the return of condensed Polychlorsilanen also high molecular weight, under the selected process conditions Polychlorsilanen with 3, 4, 5, 6, 7, 8, 9 and / or 10 Silicon atoms, which may be linear, branched and / or cyclic, is possible. The adjustment of the molecular weight of the polychlorosilanes is carried out in a simple and economical manner by adjusting the reflux, ie only monomeric chlorosilanes or additionally di- and / or trisilanes are fed again to the gas discharge reactor.

The polychlorosilane thus obtained is high to highest purity according to the above definition.

According to an alternative procedure, hexachlorodisilane is recovered in step (iv).

The chlorosilanes of the formula I leaving the gas discharge reactor, in particular the plasmatron, leaving the second column, in particular tetrachlorosilane, trichlorosilane and / or dichlorosilane, correspond in the process to unreacted chlorosilanes which are fed again for reaction to the gas discharge reactor. The particular advantage of the process and its profitability result from the return or district leadership of not in the

Gas discharge reactor reacted chlorosilanes.

Hydrogen, chlorine, hydrogen chloride, monosilane and monochlorosilane are added to the

Capacitor not condensed and discharged from the process. By the

Inventive recycling of unreacted Chlorsilanedukte and the simultaneous discharge of polychlorosilanes in the first column as sump products, can be provided with a simple design device or system a particularly economical process with extremely reduced inner surfaces. Known methods and equipment contribute significantly to the contamination of the products or the cost of the plant parts. Both the costs and the contamination could be significantly reduced with the method according to the invention and the device according to the invention.

Another advantage of the method is that in the recycling of unreacted chlorosilanes an online measurement of the molar ratios of these chlorosilanes can be done, in particular by means of IR, GC, and thus the molar addition more chlorosilanes, as reactants, can be specifically controlled to Gas discharge reactor to set a defined molar ratio between the chlorosilanes of general formula I.

According to an alternative procedure, the low boilers can be fed to the evaporator of the educt feed or the evaporator in the gas discharge reactor, so that the Chlorosilanes and optionally hexachlorodisilane are evaporated and can run off the unvaporized octachlorotrisilane in the first column.

In addition or as an alternative to one of the abovementioned process characteristics, it is preferred if defined molar mixtures of monomeric chlorosilanes of the general formula I are used in the process or defined molar ratios are set in the thermal plasma. Preferred molar ratios of tetrachlorosilane and trichlorosilane are preferably equal to or between 1:10 to 10: 1, in particular 1: 5 to 5: 1, preferably 1: 2 to 2: 1, wherein an approximately equimolar ratio for the preparation of hexachlorodisilane is preferred.

For the preparation of octachlorotrisilane it is preferred to use a) a mixture of chlorosilanes of the general formula I comprising tetrachlorosilane and dichlorosilane, in particular in a molar ratio equal to or between 1:10 and 10: 1, in particular 1: 5 to 5: 1, preferably 1: 2 to 2: 1, with an approximately equimolar ratio to the preparation of hexachlorodisilane being preferred; or b) trichlorosilane is preferably used as chlorosilane.

The high purity requirements of the produced polychlorosilane can be achieved due to the high to hochstreinen chlorosilanes used, as well as the

inventive method without the use of other chemical compounds, such as catalysts or carrier gases, etc. manages. The concrete construction of the device for producing the polychlorosilanes from monomeric chlorosilanes also allows a considerable reduction in the parts of the system and their surfaces which come into contact with the highly pure to ultrahigh-purity chlorosilanes and polychlorosilanes. Thus, the inventive construction of the plant in combination with the inventive method allows a particularly economical process management with significantly reduced contamination.

Therefore, according to the inventive method, and in particular using the device according to the invention, a highly pure octachlorotrisilane, in particular a

ultrahigh-octachlorotrisilane, a high-purity hexachlorodisilane, in particular a high-purity hexachlorodisilane, or a mixture of the two polychlorosilanes with in each case less than 1 ppm by weight of titanium. In the method according to the invention, a thermal plasma can be generated in electrical equilibrium. Thermal plasmas are plasmas that operate at elevated pressure and result in equilibrium. In the thermal plasma, the electrons T _E and the ions ΤΊ have relatively high temperature, since the free path of the particles is low and the collision frequency is high, so that a uniform

Gas temperature T _G sets, with T _E approximately equal to T | and T | approximately equal to T _G. A thermal plasma thus has a high energy density at high process temperature. The plasma is an arc plasma and, depending on the applied voltage, has currents of a few milliamperes up to a few kiloamperes. The method is preferably operated in the area of independent discharge, wherein in the region of the glow discharge (70 to 1000 V,

1 to 1000 mA), particularly preferably in the region of the arc discharge (10 to 50 V, greater than 1 A) is used. The generation of the arc plasma or of the thermal plasma takes place with the aid of a plasmatron. In general, direct, indirect and DC or

AC plasma cartridge suitable for carrying out the method according to the invention. In order to produce a preferred, homogeneous thermal plasma, becomes an indirect

Gleichstromplasmatron used.

The monomeric chlorosilane of the general formula I flows around and flows through the indirect plasmatron the arc between the cathode and anode within the plasmatron and dissociates and optionally ionizes. In order to generate a non-extinguishing arc, it is preferred to work with a DC plasma.

To carry out the process according to the invention prevails in the gas discharge reactor, a pressure of 3 to 30 000 mbar _abs . preferably from 100 to 1200 mbar _abs ..

Likewise provided by the invention are polychlorosilanes obtainable by the process described above, in particular according to one of claims 1 to 12, wherein the polychlorosilanes are a mixture comprising hexachlorodisilane, octachlorotrisilane, n-decachlorotetrasilane, tert-decachlorotetrasilane and / or dodecachloropentasilane and its structural isomers, and a content of titanium of less than or equal to 10 ppm by weight, preferably less than 8 ppm by weight, preferably less than 6 ppm by weight, more preferably less than 4 ppm by weight. The titanium content is particularly preferably less than 2 ppm by weight, and with a proportion of branched polychlorosilanes greater than or equal to 1 mol%, in particular greater than 1.5 mol%. Likewise subject of the invention is a device or a system, as shown schematically in Figures 3 and 4. The device is for carrying out the

inventive method particularly suitable. The device 0 has a

Gas discharge reactor 1, the two columns 2a, 2b are assigned. Preferably, the gas discharge reactor is a plasmatron (DC or AC), more preferably an indirect plasmatron. More preferably, the device in addition to

Gas discharge reactor, a first column 2a with a column inlet 3a for separating the Polychlorsilane upstream of the gas discharge reactor 1 and a second

Column 2b with a column inlet 4a for the separation of the low boilers and, if necessary, in the circle to leading Hexachlordisilan downstream behind the gas discharge reactor 1. In this case, the device is arranged substantially vertically, as shown in Figures 3 and 4. In addition, it is preferred if the column outlet 4b of the column 2b is associated with a condenser 5 for condensing the low boilers. For supplying the chlorosilanes in the

Gas discharge reactor is the reactor associated with a Eduktzuführung 9 (Figure 4), which in an alternative, an evaporator 10 (Figure 4) for evaporation and / or temperature control of the reactants. Alternatively, the evaporator can also be located in the gas discharge reactor.

In a particularly preferred embodiment, the condenser 5 is associated with a recirculation 6, which supplies the low-boiling components of the first column 2 a or alternatively, if appropriate, the

Gas discharge reactor, an evaporator in the gas discharge reactor or one of

Eduktzuführung associated evaporator. The lower column outlet of the first column is assigned a feed tank 7 at the bottom take-off or bottom evaporator 8.

According to the invention, as the first and / or second column so-called

Packing columns or reactive columns used, which may have, for example, Raschig rings or bubble trays. The polychlorosilanes prepared are isolated with high purity or very high purity in a feed tank 7 assigned to the column outlet 3b of the first column or a bottoms evaporator 8 assigned to the column outlet 3b.

The invention likewise relates to polychlorosilanes selected from octachlorotrisilane, hexachlorodisilane and a mixture of octachlorotrisilane and hexachlorodisilane with a titanium content of less than or equal to 1 ppm by weight,

and their use for the deposition of silicon. The polychlorosilanes prepared by the process and the polychlorosilanes according to the invention are outstandingly suitable for the deposition of layers containing high to very high silicon. By using the polysilanes according to the invention, the chlorine load at deposition and the deposition temperature can be clear

be reduced. The high-purity or high-purity dimeric, trimeric, tetrameric and / or pentameric polychlorosilanes prepared by the process according to the invention and their mixtures are highly suitable for use in the production of silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbide or silicon oxide, in particular

Production of layers of these materials as well as for the production of epitaxial

Layers, preferably by low-temperature epitaxy. These layers can be

for example via chemical vapor deposition (CVD). In addition, the produced high purity or ultrahigh purity polychlorosilanes are also suitable as starting material for the preparation of highly pure disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ). The invention will be explained in more detail with reference to the figures.

FIG. 1: Mixture containing octachlorotrisilane and hexachlorodisilane prepared by the process according to the invention, 99.34 MHz- ²⁹ Si-NMR in DMSO. FIG. 2: Polychlorosilanes comprising hexachlorodisilane, octachlorotrisilane, tert-decahlorotetrasilane, n-decachlorotetrasilane and dodecachloropentasilane prepared by the process according to the invention, 99.34 MHz- ²⁹ Si-NMR in DMSO. A = Si ₂ Cl ₆ , B = n-Si ₃ Cl ₈ , C = (Cl ₃ Si) ₃ SiCl, D = n-Si ₄ Clio and E = n-Si ₅ Cli 2 -, where component A is one mole fraction of 51, 1%, B corresponds to a mole fraction of 30.0%, C represents a mole fraction of 1.4%, D represents a molar fraction of 13.7%, E represents a mole fraction of 3.7% , The calculation is carried out by normalizing the individual surface peaks to 100%.

FIG. 3: Schematic representation of device 0 comprising a gas discharge reactor 1 and a first column 2 a and a second column 2 b as well as a condenser 5 and a return 6.

FIG. 4: Schematic representation of device 0 with bottom evaporator 8 and educt feed 9 and evaporator 10. LIST OF REFERENCES:

0 device / plant

1 gas discharge reactor

2a first column

2b second column

3a upper column exit of the first column

3b lower column exit of the first column

4a lower column exit of the second column

4b upper column exit of the first column

5 capacitor

6 feedback

7 storage tank

8 bottom evaporator

9 Feedstock feed

10 evaporators

Claims

claims

Process for the preparation of polychlorosilanes, in which chlorosilanes, comprising at least one monomeric chlorosilane of the general formula I

H _x SiCl ₄ -x (I) with x independently of one another selected from 0, 1, 2 or 3, exposed to a thermal plasma and converted to polychlorosilanes.

Method according to claim 1,

characterized,

that as polychlorosilanes polyperchlorosilanes having 2 to 8 silicon atoms are obtained, which are in particular substantially free of hydrogen,

particularly preferably hexachlorodisilane, octachlorotrisilane, decachlorotetrasilane

Dodecachloropentasilan or a mixture comprising at least two of the mentioned

Polychlorosilanes.

Method according to one of claims 1 or 2,

characterized,

that as polychlorosilane ultrahigh hexachlorodisilane, ultrapure octachlorotrisilane, high-purity decahlorotetrasilane or ultrapure dodecachloropentasilane or a mixture comprising at least two of the said compounds is isolated.

Method according to one of claims 1 to 3,

characterized,

that ultrapure hexachlorodisilane, ultrapure octachlorotrisilane, ultraprecious decachlorotetrasilane or ultrapure dodecachloropentasilane is isolated as the polychlorosilane, each having a titanium content of less than 10 ppm.

Method according to one of claims 1 to 4,

characterized,

that the starting material used is ultrapure tetrachlorosilane, ultrahigh-purity trichlorosilane and / or ultrahigh-purity dichlorosilane. Method according to one of claims 1 to 5,

characterized,

in that it is carried out in a device (0) comprising a gas-discharge reactor (1) with two columns (2a, 2b).

Method according to claim 6,

characterized,

that

- A first column (2a) with a column inlet (3a) for separating the Polychlorosilane upstream of the gas discharge reactor (1) and a second column (2b) is provided with a column inlet (4a) for separating the low boilers downstream behind the gas discharge reactor (1) , and

- the column outlet (4b) of the column (2b) a capacitor (5) for

Condensation of the low-boiling components is assigned, and

- The condenser (5) is associated with a return (6) which supplies the low boilers of the first column (2a) or the gas discharge reactor (1).

Method according to claim 6 or 7,

characterized,

that chlorosilane of the formula I and optionally chlorosilane in a mixture with

Hexachlorodisilane is introduced into the gas discharge reactor (1) or the first column (2a), in particular in the upper third, is supplied.

Method according to claim 6 or 7,

characterized,

that (i) leaving the gas discharge reactor via the second column (2b)

Chlorosilane of the formula I and hexachlorodisilane, condensed in the device (0) on the condenser (5) and (ii) via the recycle (6) in the first column (2a) are returned and, (iii) this chlorosilane of the general formula I, if appropriate in the mixture with hexachlorodisilane again through the gas discharge reactor (1), and (iv) polychlorosilanes having at least 2 silicon atoms at the column outlet (3b) of the first column (2a), in particular as Polyperchlorsilangemisch comprising Polyperchlorsilane having 2 to 8 silicon atoms, is obtained.

10. The method according to any one of claims 6 to 8,

characterized,

in that (i) they leave the gas discharge reactor via the second column (2b)

Chlorosilanes of the formula I in admixture with hexachlorodisilane in the device (0) on

Capacitor (5) is separated from hexachlorodisilane by condensing hexachlorodisilane, (ii) via recycle (6) the chlorosilanes of formula I are recycled to the first column (2a) and (iii) these chlorosilanes are again passed through the gas discharge reactor (1 ), and (iv) polychlorosilanes are recovered at the column exit (3b) of the first column (2a).

1 1. Method according to one of claims 6 to 10,

characterized,

that in the gas discharge reactor (1) a pressure of 300 to 800 mbar _abs. prevails. 12. Device (0) for carrying out a method according to one of claims 1 to 1 1, characterized in that it comprises a gas discharge reactor (1) associated with the two columns (2 a, 2 b).

13. Device according to claim 12,

characterized,

a first column (2a) having a column inlet (3a) for separating off the

Polychlorosilane upstream of the gas discharge reactor (1) and a second column (2b) are provided with a column inlet (4a) for separating the low boilers downstream behind the gas discharge reactor (1).

14. Polychlorosilanes obtainable by a process according to one of claims 1 to 12, characterized

that it is present as a mixture of polychlorosilanes, comprising hexachlorodisilane, octachlorotrisilane, n-decachlorotetrasilane, iso-decachlorotetrasilane, tert-decachlorotetrasilane and / or dodecachloropentasilane and optionally its structural isomers, and having a content of titanium of less than or equal to 10 ppm by weight and a Proportion of branched polychlorosilanes greater than or equal to 1 mol .-% is.

15. The use of polychlorosilanes selected from hexachlorodisilane, octachlorotrisilane, decachlorotetrasilane and / or dodecachloropentasilane or a mixture comprising at least octachlorotrisilane and at least one polychlorosilane selected from

Hexachlorodisilane and decachlorotetrasilane with a titanium content of less than or equal to 10 ppm by weight for the deposition of silicon.