U.S. patent application number 14/206554 was filed with the patent office on 2014-07-10 for method for producing higher silanes.
This patent application is currently assigned to Evonik Degussa GmbH. The applicant listed for this patent is Juergen Erwin LANG, Ekkehard MUEH, Hartwig RAULEDER. Invention is credited to Juergen Erwin LANG, Ekkehard MUEH, Hartwig RAULEDER.
Application Number | 20140193321 14/206554 |
Document ID | / |
Family ID | 39628085 |
Filed Date | 2014-07-10 |
United States Patent
Application |
20140193321 |
Kind Code |
A1 |
LANG; Juergen Erwin ; et
al. |
July 10, 2014 |
METHOD FOR PRODUCING HIGHER SILANES
Abstract
The invention relates to a method for producing dimeric and/or
trimeric silicon compounds, in particular silicon halogen
compounds. The claimed method is also suitable for producing
corresponding germanium compounds. The invention also relates to a
device for carrying out said method to the use of the produced
silicon compounds.
Inventors: |
LANG; Juergen Erwin;
(Karlsruhe, DE) ; RAULEDER; Hartwig; (Rheinfelden,
DE) ; MUEH; Ekkehard; (Rheinfelden, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LANG; Juergen Erwin
RAULEDER; Hartwig
MUEH; Ekkehard |
Karlsruhe
Rheinfelden
Rheinfelden |
|
DE
DE
DE |
|
|
Assignee: |
Evonik Degussa GmbH
Essen
DE
|
Family ID: |
39628085 |
Appl. No.: |
14/206554 |
Filed: |
March 12, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12524371 |
Jul 24, 2009 |
8722913 |
|
|
PCT/EP2007/064322 |
Dec 20, 2007 |
|
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14206554 |
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Current U.S.
Class: |
423/342 |
Current CPC
Class: |
C01B 21/0823 20130101;
C01B 33/12 20130101; B01J 2219/0803 20130101; B01J 2219/0894
20130101; B01J 19/088 20130101; C01G 17/00 20130101; C01P 2002/86
20130101; C01B 21/068 20130101; C01B 33/107 20130101; C01B 33/04
20130101; C07F 7/30 20130101; C01B 33/36 20130101; C07F 7/083
20130101; C01B 32/907 20170801 |
Class at
Publication: |
423/342 |
International
Class: |
C01B 33/107 20060101
C01B033/107 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2007 |
DE |
10 2007 007 874.0 |
Claims
1. A process for preparing dimeric and/or trimeric silicon
compounds of the general formula (Ia) or the germanium compounds of
the general formula (Ib) ##STR00012## where R1 to R8 are each
hydrogen and/or halogen, where the halogen is selected from
chlorine, bromine and/or iodine, where R1 to R8 denote identical or
different radicals in the formula (Ia) or (Ib), with the proviso
that at least one of the R1 to R8 radicals is a halogen, and n=0 or
1, a) wherein a silicon compound of the general formula (IIa)
##STR00013## or a germanium compound of the general formula (IIb)
##STR00014## where R9 to R12 are each hydrogen, organyl, where the
organyl comprises a linear, branched and/or cyclic alkyl having 1
to 18 carbon atoms, linear, branched and/or cyclic alkenyl having 2
to 8 carbon atoms, unsubstituted or substituted aryl and/or
corresponding benzyl, and/or halogen, and the halogen is selected
from chlorine, bromine and/or iodine, where R9 to R12 denote
identical or different radicals in the formula (IIa) or (IIb) and
n=1 or 2, the silicon compound of the formula (IIa) in the presence
of one or more compounds of the general formula (IIIa) ##STR00015##
or the germanium compound of the formula (IIb) in the presence of
one or more compounds of the general formula (IIIb) ##STR00016##
where R13 to R16 are each hydrogen, organyl, where the organyl
comprises a linear, branched and/or cyclic alkyl having 1 to 18
carbon atoms, linear, branched and/or cyclic alkenyl having 2 to 8
carbon atoms, unsubstituted or substituted aryl and/or
corresponding benzyl, and/or halogen, and the halogen is selected
from chlorine, bromine and/or iodine, where R13 to R16 denote
identical or different radicals of the formula (IIIa) or (IIIb) and
n=1 or 2, especially with the proviso that it is a
hydrogen-containing compound, is exposed to a nonthermal plasma and
b) one or more pure silicon compounds of the general formula (Ia)
or germanium compounds of the general formula (Ib) are obtained
from the resulting phase.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 12/524,371, filed on Jul. 24, 2009, which is a 371 of
PCT/EP2007/064322, filed on Dec. 20, 2007, and claims priority to
German Patent Application No. 10 2007 007 874.0, filed on Feb. 14,
2007.
[0002] The invention relates to a process for preparing dimeric
and/or trimeric silicon compounds, especially silicon-halogen
compounds. In addition, the process according to the invention is
also suitable for preparing corresponding germanium compounds. The
invention further relates to an apparatus for performing the
process and to the use of the silicon compounds prepared.
[0003] Silicon compounds used in microelectronics, for example for
producing high-purity silicon by means of epitaxy or silicon
nitride (SiN), silicon oxide (SiO), silicon oxynitride (SiON),
silicon oxycarbide (SiOC) or silicon carbide (SiC), have to meet
particularly high demands on their purity. This is true especially
in the case of production of thin layers of these materials. In the
field of application mentioned, even contaminations of the starting
compounds in the ppb to ppt range are troublesome. For example,
hexachlorodisilane in the required purity is a sought-after
starting compound in the field of electronics, in the semiconductor
industry and in the pharmaceutical industry.
[0004] To prepare the high-purity compounds mentioned, silicon
nitride, silicon oxide, silicon oxynitride, silicon oxycarbide or
silicon carbide, especially layers of these compounds,
hexachlorodisilane is converted by reaction with further nitrogen-,
oxygen- or carbon-containing precursors. Hexachlorodisilane is also
used to produce epitactic silicon layers, by means of
low-temperature epitaxy.
[0005] Known prior art processes utilize, for preparation of
halogen compounds of silicon, for example for preparation of
hexachlorodisilane (disilicon hexachloride), the reaction of
chlorine or hydrogen chloride with calcium silicide or else with
copper silicide. A further process consists in the reaction of
tetrachlorosilane (silicon tetrachloride) as it is passed over
molten silicon (Gmelin, System No. 15, Part B, 1959, pages 658 to
659). A disadvantage of both processes is the chlorination, which
takes place to an equal extent, of the impurities present in the
calcium silicide and in the silicon, which are then entrained into
the product. If the hexachlorodisilane is to be used in the
production of semiconductors, these impurities are
unacceptable.
[0006] According to the disclosure of German patent DE 1 142 848
from 1958, ultrahigh-purity hexachlorodisilane is obtained when
gaseous silicochloroform is heated to 200 to 1000.degree. C. in an
electrode burner and the gas mixture obtained is cooled and
condensed rapidly. To increase the efficiency, the silicochloroform
is diluted with hydrogen or an inert gas before the reaction.
[0007] German patent DE 1 014 971 from 1953 relates to a process
for preparing hexachlorodisilane, in which silicon tetrachloride is
reacted with a porous silicon molding at elevated temperature,
preferably at more than 1000.degree. C., in a hot wall reactor.
[0008] DE-A 3 62 493 discloses a further process for preparing
hexachlorodisilane. Here, hexachlorodisilane is prepared on the
industrial scale by reacting silicon alloys or metallic silicon
with chlorine using a vibration reactor at temperatures in the
range from 100 to 500.degree. C.
[0009] D. N. Andrejew (J. fur praktische Chemie, Series 4. Vol. 23,
1964, pages 288 to 297) describes the reaction of silicon
tetrachloride (SiCl.sub.4) in the presence of hydrogen (H.sub.2)
under plasma conditions to give hexachlorodisilane
(Si.sub.2Cl.sub.6) and higher chlorinated polysilanes. The reaction
products are obtained as a mixture. A disadvantage of this process
is that this product mixture is obtained in highly viscous to solid
form and can therefore precipitate on the reactor wall. Likewise
disclosed is the reaction of alkylsilanes such as
methyltrichlorosilane (MTCS) in the presence of hydrogen in a
plasma to give hexachlorodisilane and a multitude of undesired
by-products. What is common to both embodiments is the
disadvantageous additional requirement for hydrogen as a reducing
agent.
[0010] WO 2006/125425 A1 relates to a two-stage process for
preparing bulk silicon from halosilanes. In the first step,
preferably halosilanes, such as fluoro- or chlorosilanes, are
exposed to a plasma discharge in the presence of hydrogen. In the
second stage which follows, the polysilane mixture obtained from
the first stage is pyrolyzed to silicon at temperatures from
400.degree. C., preferably from 700.degree. C.
[0011] Features common to most of the processes mentioned are that
they proceed at high temperatures and with considerable energy
expenditure, require hydrogen as a reducing agent or lead to highly
contaminated crude products with a multitude of by-products.
[0012] It is an object of the present invention to provide an
economically viable process for preparing dimeric and/or trimeric
silicon compounds on the industrial scale, which does not have the
aforementioned disadvantages, and also an apparatus which is
suitable especially for performing the process, and the use of the
compounds prepared. The process should also be applicable to
corresponding germanium compounds.
[0013] The object is achieved by the process according to the
invention and the inventive apparatus according to the features of
embodiments 1 and 14.
[0014] The process according to the invention divides into two
process steps. In process step a), a nonthermal plasma treatment of
a silicon compound of the general formula (IIa) is effected,
optionally in the presence of one or further silicon compounds of
the general formula (IIIa), which is especially a
hydrogen-containing compound. According to the invention, the
addition of hydrogen (H.sub.2) can be dispensed with. Process step
a) is followed, in process step b), by the recovery of one or more
pure silicon compounds of the formula (Ia) from the resulting
phase, especially a distillative workup in order to remove a
reaction product formed, a silicon compound of the general formula
(Ia). Surprisingly, the silicon compound can be isolated in high
purity and also ultrahigh purity. A silicon compound of the formula
(Ia) has a high purity when impurities are present only in the ppb
range; ultrahigh purity is understood to mean impurities in the ppt
range and lower.
[0015] It has been found that, surprisingly, by a treatment of a
silicon compound which contains hydrogen, organyl and/or halogen
and is of the following general formula (IIa) by means of
nonthermal plasma, it is possible to obtain dimeric and/or trimeric
silicon compounds of the general formula (Ia). These compounds are
formed highly selectively, especially without significant
contamination by by-products, in the nonthermal plasma.
##STR00001##
[0016] The R1 to R8 radicals of the silicon compound of the general
formula (Ia) are each hydrogen and/or halogen, where the halogen is
selected from fluorine, chlorine, bromine and/or iodine, with the
proviso that at least one of the R1 to R8 radicals is a halogen
atom, where R1 to R8 may denote identical or different radicals and
the numerator n=0 or 1. Particularly preferred compounds are
hexachlorodisilane where n=0 and octachlorotrisilane where n=1, and
the R1 to R8 radicals in both compounds are chlorine. Further
preferred compounds have a numerator n=0 or 1, where the R1 to R8
radicals are all a halogen atom. In appropriate compounds, the R1
to R8 radicals are halogen and hydrogen atoms.
##STR00002##
[0017] The R9 to R12 radicals of the silicon compound of the
general formula (IIa) are each hydrogen, organyl, where the organyl
comprises a linear, branched and/or cyclic alkyl having 1 to 18
carbon atoms, linear, branched and/or cyclic alkenyl having 2 to 8
carbon atoms, unsubstituted or substituted aryl and/or
corresponding benzyl, the organyl especially containing hydrogen,
or halogen, where the halogen is selected from fluorine, chlorine,
bromine and/or iodine, and where the R9 to R12 radicals may denote
identical or different radicals and the numerator n=1 or 2. The
particularly preferred compound, silicon tetrachloride, has a
numerator of n=1 and chlorine as R9 to R12 radicals. In further
preferred embodiments, the numerator n=1 or 2 and the R9 to R12
radicals are each halogen atoms. Also appropriate are compounds
with halogen and organyl radicals or hydrogen atoms; or halogen and
organyl radicals. The compounds of the general formula (Ia) serve
as a starting substance and as a matrix in the process.
[0018] It has been found in accordance with the invention that, by
a treatment of the silicon compounds which contain hydrogen,
organyl and/or halogen and are of the following general formula
(IIa), in the presence of one or optionally more than one further
silicon compound of the general formula (IIIa), the compounds of
the formulae (IIa) and (IIIa) especially being nonidentical, by
means of nonthermal plasma, it is possible to obtain dimeric and/or
trimeric silicon compounds of the general formula (Ia). The silicon
compounds (IIa) and (IIIa) are treated in a nonthermal plasma
especially without addition of a reducing agent, for example
hydrogen.
##STR00003##
[0019] Silicon compounds of the general formula (IIIa) have, as R13
to R16 radicals, hydrogen, organyl, where the organyl comprises a
linear, branched and/or cyclic alkyl having 1 to 18 carbon atoms,
linear, branched and/or cyclic alkenyl having 2 to 8 carbon atoms,
unsubstituted or substituted aryl and/or corresponding benzyl, the
organyl especially containing hydrogen, or the radicals contain
halogen, where the halogen is selected from fluorine, chlorine,
bromine and/or iodine and where the R13 to R15 radicals may be
identical or different and the numerator n=1 or 2, where the
numerator n=1 is preferred, especially with the proviso that it is
a hydrogen-containing compound. The formation of a dimeric silicon
compound of the formula (Ia) surprisingly proceeds highly
selectively. By-products are formed only to a minor degree.
[0020] Hydrogen-containing compounds include silicon compounds
which contain hydrogen bonded to silicon and/or hydrogen to an
organyl radical.
[0021] Particularly preferred compounds of the formula (IIIa) have
a numerator of n=1 and, on the R13 to R16 radicals, chlorine and
hydrogen or an alkyl radical, for example methyl. Examples of these
compounds are trichlorosilane (HSiCl.sub.3), dichlorosilane
(H.sub.2SiCl.sub.2), monochlorosilane (H.sub.3SiCl), monosilane
(SiH.sub.4) and methyltrichlorosilane (MeSiCl.sub.3), and also
dimethyldichlorosilane (Me.sub.2SiCl.sub.2). In further appropriate
compounds, the numerator n=1 or 2, where the R13, R15 and R16
radicals are each halogen atoms and R14 is a hydrogen or an alkyl
radical. When mixtures of silicon compounds of the formulae (IIa)
and (IIIa) with a numerator of n=1 and n=2 are used, dimeric and/or
trimeric silicon compounds of the formula (Ia) can be obtained by
equilibration reactions.
[0022] In the process for preparing the silicon compound of the
formula (Ia), the silicon compound of the general formula (IIa)
where n=1 does not correspond to any of the following compounds
H.sub.mSiX.sub.4-m (X.dbd.F, Cl, Br, I; m=0-3) when the silicon
compound of the general formula (IIIa) where n=1 is one of the
compounds H.sub.mSiX.sub.4-m (X.dbd.F, Cl, Br, I; m=0-3).
[0023] According to the invention, a perhalogenated compound of the
formula (IIa) is reacted with one or more hydrogen-containing
compounds of the formula (IIIa) without addition of a reducing
agent in a nonthermal plasma to give a silicon compound of the
formula (Ia), and the pure, especially high-purity, silicon
compound of the formula (Ia) is obtained.
[0024] In a particularly preferred embodiment, dimeric and/or
trimeric silicon compounds of the formula (Ia) are obtained by
reacting silicon tetrachloride (SiCl.sub.4) of the formula (IIa)
with one or further hydrogen-containing silicon compounds of the
formula (IIIa) in nonthermal plasma.
[0025] The silicon tetrachloride here is simultaneously reactant
and matrix, and so it is typically added in an excess relative to
the hydrogen-containing compound. A considerable advantage of the
process according to the invention is that the addition of a
reducing agent, such as hydrogen, can be dispensed with. In
contrast to the known prior art processes, a mobile homogeneous
reaction mixture is obtained.
[0026] Moreover, no precipitates or oily substances form; more
particularly, the reaction mixture does not solidify in the course
of storage at room temperature. The dimeric compound of the formula
(Ia), especially the hexachlorodisilane, is advantageously formed
highly selectively, such that almost exclusively the dimeric
chlorinated silicon compound is present in the liquid reaction
product. A further product or by-product may be
octachlorotrisilane. This leads to a significantly simplified
separation of the reaction product. This makes it possible to
provide the products in a controlled manner in pure and highly pure
form, especially after a distillative purification. The silicon
compounds prepared by the process according to the invention are
suitable for use in the semiconductor industry or pharmaceutical
industry.
[0027] In the synthesis of the chlorosilanes, for example
tetrachlorosilane (SiCl.sub.4) and trichlorosilane (HSiCl.sub.3),
they are obtained as mixtures of the two compounds with further
silicon compounds, such as alkylchlorosilanes. Typically,
methylchlorosilane is present in the mixture. It is a great
advantage of the process according to the invention that these
mixtures can be supplied to the plasma without preceding
purification by distillative removal of the individual compounds.
Instead, for a given silane compound, the content of
hydrogen-containing silane compounds can be increased by metering
in trichlorosilane and/or methylchlorosilane.
[0028] Unconverted reactants of the general formula (IIa) and if
appropriate (IIIa) are fed back to the nonthermal plasma if
required. For complete conversion of the reactants to the compound
of the general formula (Ia), a cycle mode with 1 to 100 cycles can
be used; preference is given to a small number of 1 to 5 cycles;
preferably only one cycle is passed through. The silicon compounds
of the general formula (Ia) which are obtained in the nonthermal
plasma by means of the reaction are already present in pure form in
the resulting phase, from which they can be obtained in high
purity; more particularly, they are subjected to a distillative
workup. In this way, for example, hexachlorodisilane can be
isolated in ultrahigh purity from the remaining reaction products
and reactants; see FIG. 1. In the .sup.29Si NMR spectrum, aside
from the signal of the hexachlorodisilane (.delta.=7.4.+-.0.1 ppm,
DMSO), no further compounds are detectable. The contamination of
the silicon compounds with other metal compounds is at least in the
ppb range down to the ppt range, preferably in the ppt range.
[0029] The nonthermal plasma is obtained in a plasma reactor in
which a plasmatic conversion of matter is induced and is based on
anisothermal plasmas. For these plasmas, a high electron
temperature T.sub.e of .gtoreq.10.sup.4 K and relatively low gas
temperature T.sub.G.ltoreq.10.sup.3 K are characteristic. The
activation energy needed for the chemical processes is provided
predominantly through electron impacts (plasmatic conversion of
matter). Typical nonthermal plasmas can be obtained, for example,
by glow discharge, HF discharge, hollow cathode discharge or corona
discharge. The working pressure at which the inventive plasma
treatment is performed is in the range from 1 to 1000 mbar.sub.abs,
preferably 1 to 800 mbar.sub.abs, more preferably 100 to 500
mbar.sub.abs, especially 200 to 500 mbar.sub.abs, the phase to be
treated preferably being adjusted to a temperature of -40.degree.
C. to 200.degree. C., more preferably to 20 to 80.degree. C., most
preferably to 40 to 60.degree. C. In the case of germanium
compounds, the corresponding temperature may also be higher.
[0030] For a definition of nonthermal plasma and of homogeneous
plasma catalysis, reference is made to the relevant technical
literature, for example to "Plasmatechnik: Grundlagen and
Anwendungen--Eine Einfuhrung [Plasma technology: fundamentals and
applications--an introduction]; collective of authors, Carl Hanser
Verlag, Munich/Vienna; 1984, ISBN 3-446-13627-4".
[0031] In the inventive embodiment of the process, silicon
tetrachloride (SiCl.sub.4) is reacted with at least one further
hydrogen-containing silicon compound of the formula (IIIa) in a
plasma reactor for gas phase treatment, especially without addition
of a reducing agent. Examples of silicon compounds of the formula
(IIIa) include trichlorosilane, dichlorosilane, monochlorosilane,
monosilane, methyltrichlorosilane, dimethyl-dichlorosilane,
trimethylchlorosilane and/or propyltrichlorosilane.
[0032] An alternative preferred embodiment envisages the reaction
of silicon tetrachloride only with further hydrosilanes, such as
trichlorosilane. Further preferred embodiments envisage the
reaction of silicon tetrachloride only with silanes containing
organyl groups; for example, methyltrichlorosilane is added to the
tetrachlorosilane and then supplied to the reactor. Both
alternative embodiments proceed especially without addition of a
reducing agent.
[0033] Generally preferred process variants envisage a reaction of
the silicon tetrachloride with silicon compounds of the general
formula (IIIa), in which case, for example, hydrosilanes such as
trichlorosilane and/or alkylated silicon compounds such as
methyltrichlorosilane are subjected to a nonthermal plasma
treatment, especially without addition of a reducing agent.
[0034] A further advantage of the processes mentioned is that the
addition of expensive inert noble gases can be dispensed with.
Alternatively, an entraining gas, preferably an inert gas under
pressure, such as nitrogen, argon, another noble gas or mixtures
thereof can be added.
[0035] The silicon compound of the general formula (Ia) formed in
process step a) is enriched in a collecting vessel of the apparatus
for performing the process, for example in the bottom of the
apparatus, and sent to a distillative workup. Process steps a)
and/or b) can be performed batchwise or continuously. Of particular
economic interest is a process regime in which process steps a) and
b) are effected continuously. The compounds of the formula (IIa)
and if appropriate of the formula (IIIa) are fed continuously to
the plasma reactor for gas phase treatment. The higher-boiling
reaction products are separated out of the phase which forms in a
collecting vessel. It may be appropriate first to enrich the
compound of the formula (Ia) in the collecting vessel at the start
of the process, or else to feed unconverted compounds of the
formula (IIa) and/or (IIIa) back into the reactor. This can be
monitored by taking samples and analyzing them by means of FT-IR or
NMR spectroscopy. Thus, the process can suitably also be monitored
continuously ("online analysis"). As soon as the compound of the
formula (Ia) has reached a sufficient concentration in the
collecting vessel (bottom), the distillative workup to remove the
silicon compound of the general formula (Ia) can be effected in
continuous or batchwise mode. For a batchwise distillative workup,
one column is sufficient for separation. To this end, the compound
is withdrawn in high or ultrahigh purity at the top of a column
with a sufficient number of separating stages. The required purity
can be monitored by means of GC, IR, NMR, ICP-MS, or by resistivity
measurement or GD-MS after deposition of the Si.
[0036] According to the invention, the continuous workup of the
process products is effected in a column system with at least two
columns, preferably in a system with at least 3 columns. In this
way, for example, the hydrogen chloride gas (HCl) likewise formed
in the reaction can be removed by means of a so-called low boiler
column via the top, first column, and the mixture collected from
the bottom can be separated into its constituents, by
distillatively removing silicon tetrachloride (SiCl.sub.4) at the
top of a second column and hexachlorodisilane (Si.sub.2Cl.sub.6) at
the top of a third column; if appropriate, a fourth column can be
connected for removal of the octachlorotrisilane. In this way, the
reaction mixture obtained from the plasma reactor can be separated
by rectification, and the hexachlorodisilane or octachlorotrisilane
reaction product can be obtained in the desired purity. The
distillative workup of the silicon compound of the formula (Ia) can
be effected either under standard pressure or under reduced or
elevated pressure, especially at a pressure in the range from 1 to
1500 mbar.sub.abs. Preferred pressures are in the range from 40 to
250 mbar.sub.abs, especially in the range from 40 to 150
mbar.sub.abs, preferably in the range from 40 to 100 mbar.sub.abs.
The top temperature of the column for distillative workup of the
silicon compound of the formula (Ia) under reduced pressure has a
top temperature in the range from 50 to 250.degree. C.; more
particularly, the vacuum is adjusted such that the temperature is
in the range from 50 to 150.degree. C., more preferably in the
range from 50 to 110.degree. C., during the isolation of the
compound of the formula (Ia). The process products which are not
very highly contaminated in any case can be isolated in very high
to ultrahigh purity by the distillative workup. The corresponding
temperatures for workup of the germanium compounds of the formula
(Ib) may be increased somewhat.
[0037] The high-purity or ultrahigh-purity dimeric and/or trimeric
silicon compounds of the general formula (Ia) prepared by the
process according to the invention is suitable to a high degree for
use in the preparation of silicon nitride, silicon oxynitride,
silicon carbide, silicon oxycarbide or silicon oxide, especially
for production of layers of these materials and for production of
epitactic layers, preferably by low-temperature epitaxy. These
layers can be produced, for example, by means of chemical vapor
deposition (CVD). The high-purity or ultrahigh-purity dimeric
and/or trimeric silicon compounds of the general formula (Ia)
prepared by the process according to the invention are preferably
also suitable as a starting substance for the preparation of
high-purity disilane (Si.sub.2H.sub.6) or trisilane
(Si.sub.3H.sub.8).
[0038] In accordance with the general process, it is likewise
possible to obtain high-purity germanium compounds of the general
formula (Ib) from germanium compounds of the general formulae (IIb)
and (IIIb). Dimeric and/or trimeric germanium compounds of the
general formula (Ib)
##STR00004##
where R1 to R8 are each hydrogen and/or halogen, where the halogen
is selected from chlorine, bromine and/or iodine, where R1 to R8
denote identical or different radicals in the formula (Ib), with
the proviso that at least one of the R1 to R8 radicals is a
halogen, and n=0 or 1, can be prepared by exposing
[0039] a) a germanium compound of the general formula (IIb)
##STR00005##
where R9 to R12 are each hydrogen, organyl, where the organyl
comprises a linear, branched and/or cyclic alkyl having 1 to 18
carbon atoms, linear, branched and/or cyclic alkenyl having 2 to 8
carbon atoms, unsubstituted or substituted aryl and/or
corresponding benzyl, and/or halogen, and the halogen is selected
from chlorine, bromine and/or iodine, where R9 to R12 denote
identical or different radicals in the formula (IIb) and n=1 or 2,
[0040] or the germanium compound of the formula (IIb), in the
presence of one or more compounds of the general formula (IIIb)
##STR00006##
[0041] where R13 to R16 are each hydrogen, organyl, where the
organyl comprises a linear, branched and/or cyclic alkyl having 1
to 18 carbon atoms, linear, branched and/or cyclic alkenyl having 2
to 8 carbon atoms, unsubstituted or substituted aryl and/or
corresponding benzyl, and/or halogen, and the halogen is selected
from chlorine, bromine and/or iodine, where R13 to R16 denote
identical or different radicals of the formula (IIIb) and n=1 or 2,
especially with the proviso that it is a hydrogen-containing
compound, to an nonthermal plasma and
[0042] b) obtaining one or more pure germanium compounds of the
general formula (Ib) from the resulting phase. More particularly,
the phase is subjected to a distillative workup in process step
b).
[0043] All abovementioned processes and embodiments of the
processes for the silicon compounds can be applied to germanium
compounds of the general formulae (IIb) and (IIIb) for preparation
of germanium compounds of the general formula (Ib), and so it is
also possible by the process according to the invention to prepare
high-purity germanium compounds, especially Ge.sub.2Cl.sub.6 and
Ge.sub.3Cl.sub.8. According to the invention, useful reactants here
include perhalogenated germanium compounds, especially germanium
tetrachloride, germanium tetrafluoride or mixed halogen compounds,
which additionally contain organyl groups and/or hydrogen, as
compounds of the formula (IIb) and hydrogen-containing compounds of
the general formula (IIIb). These compounds can, especially after
purification, be used to dope semiconductors, especially silicon,
or to produce nanostructures.
[0044] The inventive apparatus comprises a reactor for generating
the nonthermal plasma, a collecting vessel and a column system for
distillative workup, in which case the column system for the
continuous process regime comprises at least two columns,
especially at least 3 columns. In an appropriate variant, the
column system may comprise four columns. In the batchwise process
regime, one column is sufficient. The columns are, for example,
rectification columns.
[0045] The apparatus is suitable especially for performing the
process according to the invention, in which case the reaction of
the silicon compound of the formula (IIa) with optionally one or
more compounds of the formula (IIIa) in process step a) is effected
in the reactor. According to the boiling point, the reaction
products can be enriched in a collecting vessel assigned to the
reactor or else directly partly be removed directly from the
apparatus in process step b) via a column system assigned to the
apparatus.
[0046] Use of the inventive column system in the continuous process
regime allows, for example, hydrogen chloride gas to be drawn off
directly from the apparatus via a low boiler column at the top of
the first column, then unconverted tetrachlorosilane can be
withdrawn at the top of the second column and the higher-boiling
reaction products of the general formula (Ia) at the top of the
third column. When a plurality of higher-boiling reaction products
of the formula (Ia) are isolated, a fourth column may be
assigned.
[0047] Moreover, in the apparatus, in addition to the reactor, it
is also possible to use one or more further reactors which are
connected in series or parallel. According to the invention, at
least one reactor of the apparatus is an ozonizer. A great
advantage consists in the alternatively possible use of commercial
ozonizers, such that the capital costs can be lowered
significantly. The reactors of the invention are appropriately
equipped with glass tubes, especially with quartz glass tubes, in
which case the tubes are preferably arranged in parallel or
coaxially and spaced apart by means of spacers of inert material.
Suitable inert materials are especially Teflon or glass. It is
known that the electron energy absorbed for the plasma discharge
"E" depends on the product of pressure "p" and electron distance
"d" (pd). For the process according to the invention, the product
of electron distance and pressure is generally in the range from
0.001 to 300 mmbar, preferably from 0.05 to 100 mmbar, more
preferably 0.08 to 0.3 mmbar, especially 0.1 to 0.2 mmbar. The
discharge can be induced by means of various kinds of alternating
voltages or pulsed voltages of 1 to 10.sup.6 V. Equally, the curved
profile of the voltage may, among other profiles, be rectangular,
trapezoidal, pulsed, or be composed of fragments of individual
profiles with time. Pulsed induction voltages are particularly
suitable; they enable simultaneous formation of the discharge
within the entire discharge space of the reactor. The pulse
duration in the case of pulsed operation is guided by the gas
system; it is preferably in the range from 10 ns to 1 ms. Preferred
voltage amplitudes are 10 Vp to 100 kVp, preferably 100 Vp to 10
Vp, especially 50 to 5 Vp, in a microsystem. The frequency of the
alternating voltage may be in the range from 10 MHz to 10 ns pulses
(duty ratio 10:1) down to low frequencies in the range from 10 to
0.01 Hz. For example, an alternating voltage with a frequency of
1.9 kHz and an amplitude of 35 kV "peak to peak" can be applied on
the reactor. The power input is about 40 W.
[0048] The silicon compounds of the formula (Ia) or germanium
compounds of the formula (Ib) prepared by the process according to
the invention are suitable for use in the semiconductor industry or
pharmaceutical industry, since they have impurities only in the ppb
range, preferably in the ppt range or lower. The compounds can be
prepared in high and ultrahigh purity, because the compounds are
formed surprisingly selectively in the process according to the
invention and hence only few by-products in small amounts disrupt
the workup of the process products.
[0049] The silicon compounds of the formula (Ia) prepared in
accordance with the invention are therefore suitable for preparing
silicon nitride, silicon oxynitride, silicon carbide, silicon
oxycarbide or silicon oxide, especially for producing layers of
silicon nitride, silicon oxynitride, silicon carbide, silicon
oxycarbide or silicon oxide. In addition to hexachlorodisilane
and/or octachlorotrisilane, it is appropriately also possible to
use all further silicon compounds of the formula (Ia) to prepare
the abovementioned layers. It is likewise possible to use the
silicon compounds of the general formula (Ia) prepared in
accordance with the invention, especially hexachlorodisilane and
octachlorotrisilane, as a starting substance for preparing disilane
or trisilane.
[0050] The example which follows illustrates the process according
to the invention in detail without limiting the invention to this
example.
EXAMPLE 1
[0051] Methyltrichlorosilane (MeSiCl.sub.3)-enriched silicon
tetrachloride (SiCl.sub.4), silicon tetrachloride preferably being
present in excess, is evaporated continuously and conducted into a
nonthermal plasma of a gas discharge zone of a quartz glass
reactor. The gas phase is conducted through the reactor at
approximately 250 ml/h. While the gas phase flows through the
reactor, an alternating voltage with a frequency of 1.9 kHz and an
amplitude of 35 kV "peak to peak" is applied. The power input into
the reactor is about 40 W. The operating pressure is set to about
300 mbar. After passing through the reactor, the reaction mixture
is collected in liquid form in a collecting vessel. The gas
chromatogram of the reaction mixture exhibits only one signal for
high molecular weight silicon compounds and can be assigned to
hexachlorodisilane. The distillation is effected batchwise in a
distillation apparatus with a 50 cm column with Sulzer metal
packing. At a bottom temperature of about 70.degree. C. and a
pressure of 750 mbar.sub.abs, silicon tetrachloride is distilled
off at a top temperature of about 50.degree. C. Subsequently, the
pressure is lowered to about 65 mbar.sub.abs and pure
hexachlorodisilane is distilled off at a bottom temperature around
80.degree. C. The top temperature is around 70.degree. C. The
content of metallic impurities corresponds to the detection limit
in ICP-MS. The .sup.29Si NMR spectrum exhibits only one signal for
hexachlorodisilane at -7.4 ppm; see FIG. 1.
[0052] The invention is illustrated in detail below by the working
example shown in the figure. It shows:
[0053] FIG. 1: 99.34 MHz .sup.29Si NMR spectrum of
hexachlorodisilane in DMSO, prepared by the process according to
the invention.
Embodiments
[0054] 1. A process for preparing dimeric and/or trimeric silicon
compounds of the general formula (Ia) or the germanium compounds of
the general formula (Ib)
##STR00007##
[0054] where R1 to R8 are each hydrogen and/or halogen, where the
halogen is selected from chlorine, bromine and/or iodine, where R1
to R8 denote identical or different radicals in the formula (Ia) or
(Ib), with the proviso that at least one of the R1 to R8 radicals
is a halogen, and n=0 or 1,
[0055] a) wherein a silicon compound of the general formula
(IIa)
##STR00008## [0056] or a germanium compound of the general formula
(IIb)
[0056] ##STR00009## [0057] where R9 to R12 are each hydrogen,
organyl, where the organyl comprises a linear, branched and/or
cyclic alkyl having 1 to 18 carbon atoms, linear, branched and/or
cyclic alkenyl having 2 to 8 carbon atoms, unsubstituted or
substituted aryl and/or corresponding benzyl, and/or halogen, and
the halogen is selected from chlorine, bromine and/or iodine, where
R9 to R12 denote identical or different radicals in the formula
(IIa) or (IIb) and n=1 or 2, [0058] the silicon compound of the
formula (IIa) in the presence of one or more compounds of the
general formula (IIIa)
[0058] ##STR00010## [0059] or the germanium compound of the formula
(IIb) in the presence of one or more compounds of the general
formula (IIIb)
[0059] ##STR00011## [0060] where R13 to R16 are each hydrogen,
organyl, where the organyl comprises a linear, branched and/or
cyclic alkyl having 1 to 18 carbon atoms, linear, branched and/or
cyclic alkenyl having 2 to 8 carbon atoms, unsubstituted or
substituted aryl and/or corresponding benzyl, and/or halogen, and
the halogen is selected from chlorine, bromine and/or iodine, where
R13 to R16 denote identical or different radicals of the formula
(IIIa) or (IIIb) and n=1 or 2, especially with the proviso that it
is a hydrogen-containing compound, [0061] is exposed to a
nonthermal plasma and
[0062] b) one or more pure silicon compounds of the general formula
(Ia) or germanium compounds of the general formula (Ib) are
obtained from the resulting phase. [0063] 2. The process of
embodiment 1, characterized in that the phase is subjected to a
distillative workup in process step b). [0064] 3. The process of
either of embodiments 1 and 2, characterized in that silicon
tetrachloride of the general formula (IIa) where R9 to R12=chlorine
and n=1 and at least one further hydrogen-containing compound of
the general formula (IIIa) are exposed to a nonthermal plasma in
process step a). [0065] 4. The process of embodiment 3,
characterized in that the hydrogen-containing compound of the
general formula (IIIa) used is methyl-trichlorosilane,
trichlorosilane, dichlorosilane, monochlorosilane, monosilane
and/or dimethyldichlorosilane. [0066] 5. The process of any one of
embodiments 1 to 4, characterized in that process steps a) and/or
b) are effected continuously. [0067] 6. The process of any one of
embodiments 1 to 5, characterized in that the silicon compound of
the general formula (Ia) is enriched in process step a) in a
collecting vessel of an apparatus for performing the process.
[0068] 7. The process of any one of embodiments 2 to 6,
characterized in that the distillative workup in step b) in a
continuous process regime is effected in a column system comprising
at least two columns, and in a batchwise process regime with at
least one column. [0069] 8. The process of any one of embodiments 2
to 7, characterized in that the distillative workup is effected
under standard pressure, reduced pressure or elevated pressure.
[0070] 9. The process of any one of embodiments 2 to 8,
characterized in that the distillative workup is effected at a
pressure in the range from 1 to 1500 mbar.sub.abs. [0071] 10. The
process of any one of embodiments 1 to 9, characterized in that the
distillative workup of the silicon compound of the formula (Ia) is
effected at top temperatures in the range from 40 to 250.degree. C.
[0072] 11. The process of any one of embodiments 1 to 10,
characterized in that the nonthermal plasma treatment in process
step a) is effected at pressures in the range from 1 to 1000
mbar.sub.abs. [0073] 12. The process of any one of embodiments 1 to
11, characterized in that the silicon compound of the general
formula (Ia) is hexachlorodisilane and/or octachlorotrisilane.
[0074] 13. The process of any one of embodiments 1 to 12,
characterized in that the silicon compound of the formula (Ia) has
at least a purity in the ppb range. [0075] 14. An apparatus,
especially for continuous performance of the process of embodiments
1 to 13, characterized in that it comprises a reactor for
generating the nonthermal plasma, a collecting vessel assigned
thereto and a column system for distillative workup which is
assigned thereto and comprises at least two columns. [0076] 15. The
apparatus of embodiment 14, characterized in that the reactor is an
ozonizer. [0077] 16. The apparatus of either of embodiments 14 and
15, characterized in that the reactor is equipped with glass tubes,
especially with quartz glass tubes. [0078] 17. The apparatus of any
one of embodiments 14 to 16, characterized in that the glass tubes
in the reactor are spaced apart by spacers composed of inert
material. [0079] 18. The apparatus of any one of embodiments 14 to
17, characterized in that the material of the spacers is glass or
Teflon. [0080] 19. The use of the silicon compound of the general
formula (Ia) prepared of any one of embodiments 1 to 13 for
preparing silicon nitride, silicon oxynitride, silicon carbide,
silicon oxycarbide or silicon oxide. [0081] 20. The use of
embodiment 19 for producing layers of silicon nitride, silicon
oxynitride, silicon carbide, silicon oxycarbide or silicon oxide.
[0082] 21. The use of the silicon compound of the general formula
(Ia) prepared of any one of embodiments 1 to 13 as a starting
substance for preparing disilane or trisilane.
* * * * *