Note: Descriptions are shown in the official language in which they were submitted.
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2
METHOD OF PREPARING ORGANOMETALLIC COMPOUNDS
This application claims the benefit of priority under 35 U.S.C. 119(e) of
U.S.
Provisional Patent Application No. 60/961,370 filed on July 20, 2007 and Non-
Provisional
Patent Application No. 12215828 filed on June 30, 2008.
This invention relates to methods of making organometallic compounds (OMCs).
In
particular the invention is directed to methods of making organometallic
compounds of high
purity for processes such as chemical vapor deposition.
Metal films may be deposited on surfaces, such as non-conductive (Electronic
materials applications) surfaces, by a variety of means such as chemical vapor
deposition
("CVD"), physical vapor deposition ("PVD"), and other epitaxial techniques
such as liquid
phase epitaxy ("LPE"), molecular beam epitaxy ("MBE"), chemical beam epitaxy
("CBE")
and atomic layer deposition ("ALD"). Chemical vapor deposition processes, such
as
metalorganic chemical vapor deposition ("MOCVD"), deposit a metal layer by
decomposing
organometallic precursor compounds at elevated temperatures, i.e., above room
temperature,
either at atmospheric pressure or at reduced pressures. A wide variety of
metals may be
deposited using such CVD or MOCVD processes.
For semiconductor and electronic device applications, organometallic precursor
compounds must be ultra pure and be substantially free of detectable levels of
both metallic
impurities, such as silicon and zinc, as well as other impurities including
hydrocarbons and
oxygenated compounds. Ideally, ultra purity is producing materials with level
of impurities
<0.1 wt%, preferably < I ppm, or even < I ppb. Oxygenated impurities are
typically present
from the solvents used to prepare such organometallic compounds, and are also
present from
other adventitious sources of moisture or oxygen. Achieving ultra purity is
important when
manufacturing materials for electronic applications including Group III and V
OMCs for
CVD to produce compound semi-conductors for LEDs and optoelectronic devices,
or
organometallic precursors for ALD to grow thin films for advanced silicon
chips. Some
impurities have similar boiling points in relation to the organometallic
precursor compounds
CA 02727510 2011-01-12
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making it difficult to achieve high purity with conventional distillation
technology.
Much work has been done to improve the synthetic methods for making ultra-pure
organometallic precursor compounds. Historically, organometallic precursor
compounds
have been prepared by batch processes but recently, as disclosed in U.S.
Patent No.
6,495,707 and U.S. Patent Publication No. 2004/0254389, continuous methods for
producing
organometallic compounds such as trimethylindium and trimethylgallium have
become
available.
Despite these advances, the synthesis of organometallic compounds remains
difficult.
Many of the reactions are exothermic and the production of large amounts,
particularly with
such high purity, is difficult. In addition it is difficult to scale the
production of materials to
match fluctuating demand and storage of the organometallic compounds can be
undesirable
as impurities and degradation products can be introduced.
Traditional methods used for purification include distillation,
crystallization, adduct
purification, mass-selective ultracentrifuge, and chemical treatment combined
with
distillation. While these methods provide some reduction in the level of
impurities, there is a
continuing need to produce ultra-pure organometallic compounds to meet the
performance
demands of today's most advanced electronic devices. Furthermore, there is
often an
economic constraint to the purity levels attainable with existing methods.
Excessive capital
or operating costs can limit the attainable purity due to unacceptable yield
loss, energy input,
or process cycle time due to the physical and/or chemical properties of the
impurities and the
organometallic compound.
For example, it is possible to estimate the minimum number of equilibrium
stages
required for distillation based on the relative volatility (a) of the
components and the desired
purity using the Fenske Equation. To remove the most problematic, near boiling
impurities
(a < 1.2), the number of stages, or height equivalent theoretical plates
(HETP), can exceed
50, 100, or even 200 which can require a column height of >10 meters even with
today's
most advanced packings (HETP = 0.05 to 0.20 m). A column of this size poses
difficult
scale-up and operability challenges and safety concerns from the large
inventory of
CA 02727510 2011-01-12
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pyrophoric organometallic compounds, when attempting to make ultra-pure
materials.
Accordingly, there is an ongoing need for new methods of preparing ultra-pure
organometallic compounds for use as CVD precursors.
The present invention meets this foregoing need by drawing upon the benefits
of
microchannel devices. Microchannel devices provide better control of process
conditions,
improved safety, and speed to market from laboratory development to commercial
manufacturing. A continuous flow micro-reactor, one example of a microchannel
device,
helps achieve improved synthesis yields and purity through superior heat and
mass transfer to
control the reaction conditions and minimize the risk of a reaction runaway or
hazardous spill
through low inventory of materials. The microchannel device further enables
production
scale-up by "numbering-up" multiple devices to meet market demand with no
performance
loss and at significant time and cost savings without the need for traditional
process scale-up
studies.
Microchannel devices can also be used for separation and purification steps of
reagents, solvents, intermediates, or final products with similar benefits.
The basis for the
benefits in microchannel technology arise from the high surface area provided
in the device
which enables high exchange rates between phases. Enhancement of separation is
achieved
in the microchannel architecture dimensions, typically I to 1000 microns,
through an
increased importance of interfacial phenomena and reduced distances for heat
and mass-
transfer. The superior heat and mass transfer in these devices provides high
exchange rates
between phases and better temperature control for more efficient separation
stages or lower
height equivalent theoretical plate (HETP). This enables more stages for
higher purity in a
fixed separation device geometry. There are also benefits in lower capital
intensity and lower
operating costs through improved energy efficiency by better integration of
heat exchange.
Microchannel devices can be used in a wide range of separation applications
including distillation, adsorption, extraction, absorption, and gas stripping.
CA 02727510 2011-01-12
By drawing upon the benefits of microchannel technology, the present invention
succeeds in producing ultra-pure organometallic precursor compounds.
In one aspect of the present invention there is provided a process for
preparing
organometallic metal alkyl compound compounds of ultra-high purity comprising:
reacting a metal halide solution and an alkylmetal solution in a microchannel
device to yield
a metal alkyl compound wherein the resulting compound has the minimum purity
required
for chemical vapor deposition processes.
In a second aspect of the present invention there is provided a method of
preparing a metal alkyl compound of ultra-high purity comprising purifying an
organometallic compound comprising impurities in a microchannel device to
reduce the
level of impurities with relative volativity (a) between 0.8 < a < 1.5 to a
level useful in
electronic materials applications.
As used herein, the term "metal halide" refers to a compound containing a
metal
and at least one halogen bound to the metal. The metal may also have
additional, non-
halide substituents.
As used herein, the term "electronic materials applications" refers to
applications
including but not limited to chemical vapor deposition ("CVD"), physical vapor
deposition ("PVD"), and other epitaxial techniques such as liquid phase
epitaxy ("LPE"),
molecular beam epitaxy ("MBE"), chemical beam epitaxy ("CBE") and atomic layer
deposition ("ALD"). In electronic materials applications, the level of
impurities with
relative volativity (a) between 0.8 < a < 1.5 typically must be below 100 ppm,
alternatively below 1 ppm.
"Halogen" refers to fluorine, chlorine, bromine and iodine and "halo" refers
to
fluoro, chloro, bromo and iodo. Likewise, "halogenated" refers to fluorinated,
chlorinated, brominated and iodinated. "Alkyl" includes linear, branched and
cyclic alkyl.
Likewise, "alkenyl" and "alkynyl" include linear, branched and cyclic alkenyl
and
alkynyl, respectively. The term "Group IV metal" is not intended to include
Group IV
non-metals such as carbon. Likewise, the term "Group VI metal" is not intended
to
include Group VI non-metals such as
CA 02727510 2011-01-12
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oxygen and sulfur. "Aryl" refers to any aromatic moiety, and preferably an
aromatic
hydrocarbon.
The articles "a" and "an" refer to the singular and the plural.
As used herein, "CVD" is intended to include all forms of chemical vapor
deposition
for example: Metal Organic Chemical Vapor Deposition (MOCVD), Metal Organic
Vapor
Phase Epitaxy (MOVPE), Oganometallic Vapor Phase Epitaxy (OMVPE),
Organometallic
Chemical Vapor Deposition (OMCVD) and Remote Plasma Chemical Vapor Deposition
(RPCVD). In CVD processes organometallic compounds must have a purity of at
least
99.9999% in order to meet stringent electrical or optoelectronic performance
requirements of
semiconducting devices produced using these organometallic compounds.
Unless otherwise noted, all amounts are percent by weight and all ratios are
molar
ratios. All numerical ranges are inclusive and combinable in any order except
where it is
clear that such numerical ranges are constrained to add up to 100%.
Microchannel devices offer novel opportunities in chemical synthesis and
purification. Microchannel devices have channel cross-section dimensions
(widths) of 0.1 to
5,000 micrometers, preferably l to 1,000 micrometers, or more preferably, 1 to
100
micrometers. Microchannel devices are typically comprised of multiple channels
for fluid
flow in parallel to the primary flow direction. Due to the small channel cross-
section
dimensions, the microchannel device has a high surface area to volume ratio
resulting in
highly efficient mass and heat transfer. In particular, mass transfer is on
the molecular scale
and heat transfer coefficients can be up to 25 kilowatts/square meterKelvin or
more. For
comparison, heat transfer coefficients of conventional jacketed reactors are
typically 0.1 to
0.2 kilowatts/square meterKelvin. The highly efficient mass and heat transfer
in a
microchannel device permits much tighter control of reaction conditions such
as temperature,
reactant concentration and residence time. Temperature control is particularly
important for
preparation of high purity organometallic products. Deviations from isothermal
conditions
for exothermic or endothermic reactions can lead to increased amounts of
undesired side
products resulting in lower product yield and purity. Precise temperature
control in the
CA 02727510 2011-01-12
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production of high purity products decreases or, in some cases eliminates, the
need for
subsequent purification, thus decreasing the overall amount of resources
required to produce
the organometallic compound.
As each microchannel device typically produces a small quantity of
organometallic
precursor, a number of microchannel devices may be used in parallel. Total
volume
produced by the series of microchannel devices can be controlled by increasing
or decreasing
the number of micrchannel devices in use at any given point in time, thus
decreasing or
eliminating the need for product storage.
Microchannel devices may be made from any conventional material including but
not limited to metals, polymers, ceramics, silicon or glass. Exemplary metals
include but are
not limited to metal alloys, such as HastelloyT"' alloys, readily available
from Haynes
International, Inc., and austenitic stainless steels such as, for example,
304, 312, and 316
stainless steels. Methods of fabrication include but are not limited to
mechanical micro-
machining, molding, tape casting, etching, laser patterning, sandblasting, hot
embossing,
lithography, and micro-stereolithography. The microchannel device may be
constructed
with both smooth channel walls and/or channels with structural features on the
channel walls
that enhance heat and mass transfer. A microreactor is one example of a
microchannel
device.
In some microchannel device embodiments used for conducting reactions, the
microreactor comprises an inlet for each reagent. In reactions employing three
or more
reagents, two or more reagents may be combined and fed to the microreactor via
a single inlet
with the proviso that the total number of reagents is not combined until in
the microreaction
zone. For example, when the reaction employs three reagents, two of the
reagents may be co-
fed to the microreactor via the same inlet and the third reagent may be fed
via a second inlet.
The microchannel device can comprise a separate channel system for temperature
control via an external cooling or heating source. Exemplary systems include,
but are not
limited to hot oil, hot water, hot steam, cold oil, cold water, cold baths,
and refrigeration
CA 02727510 2011-01-12
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units. As used herein, by "hot" is meant temperatures above room temperature,
typically
above 35 C. As used herein, by "cold" is meant temperatures below room
temperature,
typically below 15 C. In the case of a microreactor, the device is operated at
a temperature
appropriate for the particular synthesis reactions.
The microchannel device may further comprise a micromixer for mixing of the
inlet
streams.
The microchannel device can have a length ranging from 1 micrometer to 1
meter, or
greater, depending on the process requirements or the device fabrication
method. Multiple
microchannel devices can be used sequentially if required to achieved the
desired overall
length. In the case of a microreactor, the length of the microchannel device
is dictated by the
kinetics of the particular reaction being performed in addition to the flow
rate and
temperature. Slower reactions require a longer residence time in the
microreactor and hence
a longer microreactor. Additionally, when sequential reactions are desired the
microreactor
can comprise additional inlets along the length of the device or between
devices for
additional reagents.
The microchannel device comprises an outlet for the removal of product. In
some
embodiments the microchannel device comprises two outlets, one for a liquid
stream and one
for a gaseous stream. The product streams from a microreactor may then be
subjected to
purification, using either conventional purification methods, microchannel
purification, or a
combination thereof.
An example of a microreactor is disclosed in U.S. Patent 6,537,506 which
describes a
stacked plate, multichannel reactor incorporating heat transfer fluid
pathways, reactant fluid
pathways, product pathways, mixing chambers and reaction chambers. _
The microchannel device may optionally contain a wick or membrane structure to
control the liquid film thickness and enhance interfacial phenomena.
Microchannel devices
may be used for fluid separation including distillation. The application of
microchannel
devices to a commercially important distillation application is the C2
splitter, which separates
ethane from ethylene. The microchannel distillation process can reduce energy
consumption
CA 02727510 2011-01-12
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and capital costs for ethylene production.
The present invention provides a process for preparing an organometallic
compound
by reacting a metal salt with an alkylating agent in a microchannel device to
produce an ultra-
pure alkylmetal compound for processes such as chemical vapor deposition.
Additionally the
alkylating agents of the present invention may themselves be purified.
Examples of metal salt and alkylating agent combinations include but are not
limited
to reacting a metal halide with a trialkylaluminum solution, a metal halide
solution with an
alkyl magnesium halide, or a metal halide solution with an alkyl lithium
solution in a
microchannel device, such as a microreactor, to produce an alkyl
metal,compound. In some
embodiments the molar ratio of alkylating agent to metal salt is greater than
or equal to one.
In some embodiments the molar ratio is greater than or equal to 2. In some
embodiments the
molar ratio is greater than or equal to 3.
The metal halide may comprise a Group II, Group 111, Group IV, or Group V
metal.
There are a sufficient number of halogens present in the metal halide to form
a neutral
compound. Exemplary metal halides include, but are not limited to, ZnCI2,
GaCI3i InCI3,
InBr3i InI3, GeCI4, SiCI4, SnCl4i PCl3, AsC13i SbCI3 and BiCI3.
The trialkylaluminum solution comprises three alkyl groups, which may be the
same
or different. Each alkyl group comprises 1 to 8 carbons. The alkyl groups may
be straight
chain, branched or cyclic. The alkyl magnesium halide and alkyl lithium
compounds
comprise a single alkyl group comprising I to 8 carbons. Likewise, the alkyl
groups may be
straight chain, branched or cyclic.
The metal salt solution and the alkylating agent solution may comprise any
organic
solvent which is inert to the reaction between the two constituents and is
also inert to any
products resulting from the reaction. In some embodiments the metal salt
solution is free of
solvent, i.e., the metal salt is already in liquid form and is added "neat".
The solvent should
be chosen to provide sufficient solubility for the reaction to proceed. The
metal salt solution
and the alkylating agent solution may use the same or different solvents.
Particularly suitable
organic solvents include, but are not limited to, hydrocarbons and aromatic
hydrocarbons.
CA 02727510 2011-01-12
Exemplary organic solvents include, without limitation, benzene; alkyl
substituted benzenes
such as toluene, xylene, and (C4-C20)alkyl benzenes such as (C10-C12)alkyl
benzenes and
(C,0-C70)alkyl biphenyls; and aliphatic hydrocarbons such as pentane, hexane,
heptane,
octane, decane, dodecane, squalane, cyclopentane, cyclohexane, and
cycloheptane; and
mixtures thereof. More preferably, the organic solvent is benzene, toluene,
xylene, (C4-
C20)alkyl benzenes, hexane, heptane, cyclopentane or cyclohexane. It will be
appreciated
that more than one organic solvent may be advantageously used. Such organic
solvents are
generally commercially available from a variety of sources, such as Aldrich
Chemicals
(Milwaukee, Wis.). Such solvents may be used as is or, preferably, purified
prior to use.
Preferably, such organic solvents are dry and deoxygenated prior to use. The
solvents
may be deoxygenated by a variety of means, such as purging with an inert gas,
degassing the
solvent in vacuo, or a combination thereof. Suitable inert gases include
argon, nitrogen and
helium, and preferably argon or nitrogen.
In an alternative embodiment, ionic liquids will be employed as the solvents
that do
not interact with organometal lie synthesis under consideration, and offer
"green sovents" that
are environment-friendly. Ionic liquids are generally salts that are liquid at
low temperatures,
having melting points under 100 C. Many ionic liquids remain in the liquid
phase at room
temperature, and are referred to as room temperature ionic liquids. Ionic
liquids are
composed entirely of ions and typically they arc composed of bulky organic
cations and
inorganic anions. Due to the high Coulombic'forces in these compounds, ionic
liquids have
practically no vapor pressure.
Any suitable ionic liquid may be employed in the present invention. Exemplary
cations used in ionic liquids include, but are not limited to,
hydrocarbylammonium cations,
hydrocarbylphosphonium cations, hydrocarbylpyridinium cations, and
dihydrocarbylimidazolium cations. Exemplary anions useful in the present ionic
liquids
include, but are not limited to, chlorometalate anions, fluoroborate anions
such as
tetrafluoroborate anions and hydrocarbyl substituted fluoroborate anions, and
CA 02727510 2011-01-12
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fluorophosphate anions such as hexafluorophosphate anions and a hydrocarbyl
substituted
fluorophosphate anions. Examples of chlorometalate anions include, but are not
limited to,
chloroaluminate anion such as tetrachloroaluminate anion and a
chlorotrialkylaluminate
anion, chlorogallate anions such as chlorotrimethylgallate and tetrachloroga I
late,
chloroindate anions such as tetrachloroindate and chlorotrimethylindate.
Suitable chloroaluminate-based ionic liquids include, without limitation,
those
having a hydrocarbyl substituted ammonium halide, a hydrocarbyl substituted
phosphonium
halide, a hydrocarbyl substituted pyridinium halide, or a hydrocarbyl
substituted imidazolium
halide. Exemplary chloroaluminate-based ionic liquids include, but are not
limited to,
trimethylphenyl ammonium chloroaluminate ("TMPACA"), benzyltrimethyl ammonium
chloroaluminate ("BTMACA"), benzyltriethyl ammonium chloroaluminate
("BTEACA"),
benzyltributyl ammonium chloroaluminate (`BTBACA"), trimethylphenyl
phosphonium
chloroaluminate ("TMPPCA"), benzyltrimethyl phosphonium chloroaluminate
("BTMPCA"), benzyltriethyl phosphonium chloroaluminate ("BTEPCA"),
benzyltributyl
phosphonium chloroaluminate ("BTBPCA"), I-butyl-4-methyl-pyridinium
chloroaluminate
(`BMPYCA"), 1=-butyl-pyridinium chloroaluminate ("BPYCA"), 3-methyl- I -propyl-
pyridinium chloroaluminate ("MPPYCA"), I-butyl-3-methyl-imidazolium
chloroaluminate
("BMIMCA"), I-ethyl-3-methyl-imidazolium chloroaluminate ("EMIMCA"), I-ethyl-3-
methyl-imidazolium bromo-trichloroaluminate ("EMIMBTCA"), 1-hexyl-3-methyl-
imidazolium chloroaluminate ("HMIMCA"), benzyltrimethyl ammonium
chlorotrimethylaluminate ("BTMACTMA"), and I -methyl-3-octyl-imidazolium
chloroaluminate ("MOIMCA").
Other suitable ionic liquids include those having a fluoroborate anion or a
fluorophosphate anion, such as, but not limited to, trimethylphenyl ammonium
fluoroborate
("TMPAFB"), benzyltrimethyl ammonium fluoroborate ("BTMAFB"), benzyltriethyl
ammonium fluoroborate ("BTEAFB"), benzyltributyl ammonium fluoroborate
("BTBAFB"),
trimethylphenyl phosphonium fluoroborate ("TMPPFB"), benzyltrimethyl
phosphonium
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fluoroborate ("BTMPFB"), benzyltriethyl phosphonium fluoroborate ("BTEPFB"),
benzyltributyl phosphonium fluoroborate ("BTBPFB"), 1-butyl-4-methyl-
pyridinium
fluoroborate ("BMPFB"), I-butyl-pyridinium fluoroborate ("BPFB"), 3-methyl-l-
propyl-
pyridinium fluoroborate ("MPPFB"), I -butyl-3-methyl-imidazolium fluoroborate
("BMIMFB"), 1-ethyl-3-methyl-imidazolium fluoroborate ("EMIMFB"), I-ethyl-3-
methyl-
imidazolium bromo-trifluoroborate ("EMIMBTFB"), 1-hexyl-3-methyl-imidazolium
fluoroborate ("HMIMFB"), 1-methyl-3-octyl-imidazolium fluoroborate ("MOIMFB"),
and
benzyltrimethyl ammonium fluorophosphate (`BTMAFP").
Ionic liquids are generally commercially available or may be prepared by
methods
known in the art. These compounds may be used as is or may be further
purified.
The concentration and amounts of the solutions are chosen such that the molar
ratio of
the alkylating agent compound to the metal salt is greater than or equal to
the stoichiometric
requirement for the particular alkylation reaction.
The metal halide with a trialkylaluminum solution reaction may be performed at
-10
to 100 T. Useful pressures are I to 10 bar.
The metal halide solution with an alkyl magnesium halide or an alkyl lithium
solution
reaction may be performed at -50 to 50 T. Useful pressures are I to 10 bar.
In another embodiment of the present invention, there is provided a method to
prepare
metal amidinate compounds that'are useful sources suitable for Atomic Layer
Deposition
(ALD). The metal amidinate composition is an organometallic compound suitable
for use as
an ALD precursor having the formula (R'NCR2NR3)õM+mL'(m_n)L2P, wherein R', R2
and R'
are independently chosen from H, (Ci-C6)alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl,
dialkylamino, di(silyl-substituted alkyl)amino, disilylamino, di(alkyl-
substituted silyl)amino,
and aryl; M = a metal; L' = an anionic ligand; L2 = a neutral ligand; m = the
valence of M; n
= 0-6; p = 0-3; and wherein in > n. Metal amidinates can be homoleptic or
heteroleptic in
nature, i_e. may comprise of different amidinate ligands or a combination of
amidinates and
other anioinic ligands. Such compounds are suitable in a variety of vapor
deposition methods,
CA 02727510 2011-01-12
13
such as chemical vapor deposition ("CVD"), and are particularly suitable for
atomic layer
deposition ("ALD"). Also provided is a composition including the above
described
compound and an organic solvent. Such a composition is particularly suitable
for use in
ALD and direct liquid injection ("DLI") processes.
The method of preparing an organometallic amidinate compound comprises
reacting a
metal halide solution with an amidinato lithium solution in a microchannel
device such as a
microreactor to produce a metal alkylamidinate compound, wherein the molar
ratio of
amidinatolithium compound to metal halide is greater than or equal to one. In
some
embodiments the molar ratio is greater than or equal to 2. In some embodiments
the molar
ratio is greater than or equal to 3.
The metal halide may comprise a Group II through Group VIII metal. There are a
sufficient number of halogens present in the metal halide to form a neutral
compound.
Exemplary metal halides include ZnCl2i GaCl3, InBr3, AiC13, HfC14, ZrCl4i
GeCI4,.SiCI4,
TaCI5, WCl6, SbC13 and RuCl3.
The amidinatolithium compound comprises a single amidinato group comprising
alkyl or aryl or cyclic groups with 1 to 8 carbons. The alkyl groups may be
straight chain,
branched, or cyclic.
The metal halide solution and the amidinatolithium solution may comprise any
solvent which is inert to the reaction between the metal halide and the
amidinato lithium
solution and is also inert to any products resulting from the reaction. The
solvents and
reagents need to be dry, and deoxygenated. The solvent should be chosen to
provide
sufficient solubility for the reaction to proceed. The metal halide solution
and the amidinato
lithium solution may use the same or different solvents. Exemplary solvents
include, but are
not limited to the aforementioned list.
In some embodiments the metal halide solution is free of solvent, i.e., the
metal halide
is already in liquid form and is added "neat". The concentration and amounts
of the solutions
is chosen such that the molar ratio of the amidinato lithium compound to the
metal halide is
CA 02727510 2011-01-12
14
greater than or equal to the stoichiometric ratio required for the desired
reaction.
The reaction may be performed at -50 to 50 C. Useful pressures are I to 10
bar.
In yet another embodiment, a method of preparing an organometallic compound
comprises, reacting a metal halide solution with an alkyl metal solution in
the presence of a
tertiary amine, a tertiary phosphine, or a mixture of a tertiary amine and a
tertiary phosphine
in a microchannel device such as a microreactor.
In particular the method comprises reacting a metal halide of the formula
R,"MX¾m
with a Group III compound of the formula R4nM'X'3.,, in the presence of a
tertiary amine or a
tertiary phosphine or mixtures of a tertiary amine and a tertiary phosphine in
an organic
solvent to provide an alkylmetal compound, wherein each R is independently
chosen from H,
alkyl, alkenyl, alkynyl and aryl; M is chosen from a Group IV metal and a
Group VI metal;
each X is independently a halogen; each R4 is independently chosen from (C,-
C6)alkyl; M' is
a Group III metal; each X' is independently a halogen; m=0-3; and n=1-3. The
Group IV
metal halides and the Group VI metal halides are generally commercially
available, such as
from Gelest, Inc. (Tullytown, Pa.), or may be prepared by methods known in the
literature.
Such compounds may be used as is or may be purified prior to use. It will be
appreciated by
those skilled in the art that more than one metal halide, more than one Group
III compound,
and combinations thereof may be used.
Exemplary Group IV metals include, but are not limited to, silicon, germanium
and
tin. Exemplary Group VI metals include, without limitation, tellurium and
selenium. M is
preferably silicon, germanium or tin and more preferably germanium. X may be
any halogen.
Each X may be the same or different. In one embodiment, m=0. When m=0, a Group
IV or
Group VI metal tetrahaiide is used. In other embodiments, m may be 1, 2 or 3.
A wide variety of alkyl, alkenyl and alkynyl groups may be used for R.
Suitable alkyl
groups include, without limitation, (C,-C,z)alkyl, typically (C,-C6)alkyl and
more typically
(C,-C4)alkyl. In one embodiment, the alkyl groups are bulky alkyl groups. By
"bulky alkyl
group" is meant any sterically hindered alkyl group. Such bulky alkyl groups
have at least
three carbons, there being no particular upper limit to the number of carbons
in such group. It
CA 02727510 2011-01-12
is preferred that the bulky alkyl groups each have from three to six carbon
atoms, and more
preferably three to five carbon atoms. Such bulky alkyl groups are preferably
not linear, and
are preferably cyclic or branched. Exemplary alkyl groups include methyl,
ethyl, n-propyl,
iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, cyclopentyl,
hexyl, and
cyclohexyl. More typically, suitable alkyl groups include ethyl, iso-propyl,
and tert-butyl.
Suitable alkenyl groups include, without limitation, (C2-C12)alkenyl,
typically (C2-C6)alkenyl
and more typically (C2-C4)alkenyl. Exemplary alkenyl groups include vinyl,
allyl, methallyl
and crotyl. Typical alkynyl groups include, without limitation, (C2-
C17)alkynyl, typically (C2-
C6)alkynyl and more typically (C2-C4)alkynyl. Suitable aryl groups are (C6-
C10)aryl,
including, but not limited to, phenyl, tolyl, xylyl, benzyl and phenethyl.
When two or more
alkyl, alkenyl or alkynyl groups are present, such groups may be the same or
different.
Any of the above alkyl, alkenyl, alkynyl or aryl groups of R may optionally be
substituted, such as with halogen or dialkylamino. By "substituted" it is
meant that one or
more hydrogens on the alkyl, alkenyl, alkynyl or aryl group are replaced with
one or more
halogens or dialkylamino groups.
A wide variety of Group III compounds may be used. Suitable Group III
compounds
useful in the present invention typically have the formula R4nM'X'3.,,,
wherein each R4 is
independently selected from (C1-C6)alkyl; M' is a Group IIIA metal; X' is
halogen; and n is
an integer from 1 to 3. M' is suitably boron, aluminum, gallium, indium and
thallium, and
preferably aluminum. Preferably, X' is selected from fluorine, chlorine or
bromine. Suitable
alkyl groups for R4 include, but are not limited to, methyl, ethyl, n-propyl,
iso-propyl, n-
butyl, iso-butyl, and tert-butyl. Preferred alkyls include, methyl, ethyl, n-
propyl and iso-
propyl. In one embodiment, n is 3. Such Group III compounds where n is 3
include
trialkylboron, trialkylaluminum, trialkylgallium, trialkylindium and
trialkylthallium, with
trialkylaluminum compounds being preferred. In an alternate embodiment, n is 1
or 2. Such
Group IIIA compounds where n is 1-2 include dialkylaluminum halides such as
dialkylaluminum chlorides. Group III compounds are generally available
commercially from
a variety of sources, such as Gelest, or may be prepared by a variety of
methods known in the
CA 02727510 2011-01-12
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literature. Such compounds may be used as is or may be purified prior to use.
Suitable tertiary amines include, but are not limited to, those having the
general
formula NR5R6R', wherein R5, R6 and R' are independently selected from (C1-
C6)alkyl,
di(C,-C6)alkylamino-substituted (C,-C6)alkyl, and phenyl and wherein R5 and R6
may be
taken together along with the nitrogen to which they are attached to form a 5-
7 membered
heterocyclic ring. Such heterocyclic ring may be aromatic or non-aromatic.
Particularly
suitable tertiary amines include, but are not limited to, trimethylamine,
triethylamine, tri-n-
propylamine, tri-n-butylamine, tri-iso-propylamine, tri-iso-butylamine,
dimethylaminocyclohexane, diethylaminocyclohexane, dimethylaminocyclopentane,
diethylaminocyclopentane, N-methylpyrrolidine, N-ethylpyrrolidine, N-n-
propylpyrrolidine,
N-iso-propylpyrrolidine, N-methylpiperidine, N-ethylpiperidine, N-n-
propylpiperidine, N-
iso-propylpiperidine, N,N'-dimethylpiperazine, N,N'-diethylpiperazine, N,N'-
dipropylpipcrazine, N,N,N',N'-tetramethyl-1,2-diaminoethane, pyridine,
pyrazine,
pyrimidine, and mixtures thereof. Preferred amines include trimethylamine,
triethylamine, tri-
n-propylamine, triiso-propylamine, and tri-n-butylamine. In one embodiment,
the tertiary
amine is triethylamine or tri-n-propylamine.
Exemplary tertiary phosphines include, without limitation, those of the
general
formula RRR9R10P, where R8, R9, and R'0 are independently chosen from (C,-
C6)alkyl, phenyl
and (C1-C6)alkyl-substituted phenyl. Suitable tertiary phosphines include
triethyl phosphine,
tripropyl phosphine, tributyl phosphine, phenyl dimethyl phosphine, phenyl
diethyl
phosphine and butyl diethyl phosphine.
It will be appreciated by those skilled in the art that more than one tertiary
amine or
tertiary phosphine may be used. Mixtures of a tertiary amine and a tertiary
phosphine may
also be used. Such tertiary amines and tertiary phosphines are generally
commercially
available from a variety of sources. Such tertiary amines and tertiary
phosphines may be
used as is or, preferably further purified prior to use.
A wide variety of organic solvents may be used. Typically, such organic
solvents do
not contain oxygenated species such as ether linkages, and are preferably free
of oxygen.
CA 02727510 2011-01-12
17
Exemplary organic solvents include, but are not limited to, hydrocarbons and
aromatic
hydrocarbons. Suitable organic solvents include, without limitation, benzene,
toluene, xylcne,
pentane, hexane, heptane, octane, decane, dodecane, squalane, cyclopentane,
cyclohexane,
cycloheptane, and mixtures thereof. It will be appreciated that more than one
organic solvent
may be advantageously used in the present invention. In an alternative
embodiment, the
tertiary amine may be used as the organic solvent. Such organic solvents are
generally
commercially available from a variety of sources, such as Aldrich Chemicals
(Milwaukee,
Wis.). Such solvents may be used as is or, preferably, purified prior to use.
Preferably, such organic solvents are deoxygenated prior to use. The solvents
may be
deoxygenated by a variety of means, such as purging with an inert gas,
degassing the solvent
in vacuo, or a combination thereof. Suitable inert gases include argon,
nitrogen and helium,
and preferably argon or nitrogen.
The specific tertiary amine, tertiary phosphine and organic solvent used
depend upon
the particular alkylmetal compound desired. For example, the organic solvent
and tertiary
amine may be selected such that they are more volatile or less volatile than
the desired
alkylmetal compound. Such differences in volatility provide easier separation
of the
alkylmetal compound from both the amine and organic solvent. The selection of
the tertiary
amine and the organic solvent are well within the abilities of those skilled
in the art.
In general, the tertiary amine and/or tertiary phosphine is present in a
stoichiometric
amount to the Group IIIA compound. The mole ratio of the metal halide to the
Group IIIA
compound may vary over a wide range, such as from 1:0.1 to 1:5, the particular
mole ratio
being dependent upon the alkylmetal compound desired. Another suitable range
of mole
ratios is from 1:0.5 to 1:2. Mole ratios greater than 1:5 are also expected to
be effective.
The particular alkylmetal compound obtained from the present method can be
controlled by selection of the mole ratio of the metal halide and the Group
IIIA compound,
i.e. the number of halogens replaced in the metal halide compound can be
controlled by the
number of moles of Group III compound. For example, in the reaction of a Group
IV metal
tetrahalide (A), such as germanium tetrachloride, with a trialkylaluminum (B),
such as
CA 02727510 2011-01-12
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trimethylaluminum, a mole ratio of 1:0.5 (A:B) provides an alkyl Group IV
metal trihalide; a
mole ratio of 1:1 (A:B) provides a dialkyl Group IV metal dihalide; a mole
ratio of 1:1.5
(A:B) provides a trialkyl Group IV metal halide; and a mole ratio of 1:2 (A:B)
provides a
tetraalkyl Group IV metal. Thus, one, two, three or four halogens of the metal
halide
compound may be replaced according to the present method.
In one embodiment, the Group III compound, tertiary amine and/or tertiary
phosphine
and organic solvent may be combined in any order prior to reaction with the
metal halide. In
a further embodiment, the Group 111 compound is first combined with the
tertiary amine
and/or tertiary phosphine to form an amine-Group III adduct or a phosphine-
Group III
adduct. Typically, the amine-Group III adduct may be formed at a wide variety
of
temperatures. Suitable temperatures for forming the adduct are from ambient to
90 C. The
metal halide is then reacted with the amine-Group III adduct to form the
desired alkylmetal
compound. It is preferred that the metal halide is added dropwise, either neat
or as a
hydrocarbon solution, to the amine-Group Ill adduct. Alternatively, the amine-
Group Ill
adduct may be added dropwise to the metal halide, either neat or as a
hydrocarbon solution.
Suitable temperatures to form the alkylmetal compound are from ambient to 80
C. Thus, in
one embodiment, the present invention provides a method for preparing
alkylmetal
compounds comprising reacting a Group III compound with a tertiary amine to
form an
amine-Group Ill adduct in an organic solvent that is free of oxygenated
species; and reacting
the amine-Group Ill adduct with a Group IV metal halide, Group VIA metal
halide or a
mixture thereof in the organic solvent. When a tertiary phosphine is used in
the above
reactions, a phosphine-Group III adduct is formed.
In another embodiment, the metal halide may be combined with the Group Ill
compound and optionally an organic solvent prior to mixing with the tertiary
amine and/or
tertiary phosphine. The tertiary amine and/or tertiary phosphine and
optionally an organic
solvent may then be combined with the metal halide-Group IIIA compound mixture
using
suitable mixing zones within the microchannel device or conventional external
agitation
techniques. Alternatively, the metal halide-Group Ill compound may be added to
the tertiary
CA 02727510 2011-01-12
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amine and/or tertiary phosphine and optionally an organic solvent. While not
intending to be
bound by theory, it is believed that the transalkylation reaction does not
begin until the metal
halide, Group III compound and tertiary amine are combined.
Alternatively, the alkylmetal compound may be prepared in a continuous manner.
For
example, the metal halide and the Group III compound may be independently
added in a
continuous manner to a microchannel reactor and contacted with a tertiary
amine and/or
tertiary phosphine in a suitable solvent, such as an aromatic or aliphatic
hydrocarbon. The
addition of the metal halide and the Group III compound can be controlled by a
variety of
suitable means, such as by the use of mass flow controllers. In such a
continuous process, the
desired alkylmetal compound may be recovered, such as by distillation, while
the metal
halide and Group III compound are being added to the reaction zone. In a
further alternative,
a mixture of the metal halide and the Group III compound may be combined with
the tertiary
amine and/or tertiary phosphine in a suitable solvent. In such a continuous
process, the
dcsired alkylmetal compound may be recovered, such as by distillation, while
the metal
halide/Group III compound mixture is being added to the reaction zone.
The organometallic compounds may be used as is or suitably purified by a
variety of
techniques, such as by distillation, sublimation, and recrystallization. The
present method
provides organometallic compounds that are substantially free of metallic
impurities such as
aluminum, gallium, indium, cadmium, mercury and zinc. The organometallic
compounds are
also substantially free of oxygenated impurities such as ethereal solvents,
and preferably free
of such oxygenated impurities. By "substantially free" it is meant that the
present compounds
contain less than 0.5 ppm of such impurities. The present organometallic
compounds have a
purity of at least 99.99% or alternatively 99.9999% by weight. Specifically,
the
organometallic compounds of the present invention comprise impurity levels by
weight of
less than 100 ppm to less than 1 ppm.
Organometallic compounds with ultra-high purity for electronic materials
applications
can be further purified using microchannel devices. The microchannel device
can be used to
purify the reactants, intermediates, or final products or combinations thereof
to achieve ultra-
CA 02727510 2011-01-12
high purity compounds for electronic applications. The organometallic
compounds can be
produced in microchannel reactors as described above, or in traditional
reactors including
batch stirred tanks, semi-batch, continuous flow stirred tanks, continuous
flow tubular
reactors, reactive distillation reactors, and other known methods. Ultra-high
purity material
for electronic applications is often difficult to achieve via conventional
thermal separation
methods such as distillation and sublimation, or by mass transfer separation
methods such as
extraction, absorption and adsorption due to low concentration driving forces.
Organometallic compounds containing impurities with near boiling points
(relative
volatility, 0.8 < a < 1.5, where a = the vapor pressure of the impurity/vapor
pressure of
desired pure compound) are especially difficult to purify via staged
distillation processes
with conventional packing. The column may require a large number of stages,
>50, >100,
sometimes >200, or high reflux ratios, >I 0, >20, sometimes >50, or both,
which adds to the
investment and operating cost and complexity of the process. The microchannel
device
provides an improved solution to these problems. The small channel dimensions
generate
higher transport gradients to intensify heat and mass transfer, and increased
surface to
volume provides higher effective exchange area in a fixed geometry. Both
factors contribute
to more efficient separation (smaller Height Equivalent Theoretical Plate,
HETP) for
purification, especially beneficial for attaining high purity.
Ultra high purity organometallic compounds can also be produced in a
microchannel
device by adsorptive or chemical purification technique such as adduct-
purification. A
selective adsorbent or adduct-forming Lewis base such as an amine, phosphine,
or ether can
be supported on microchannel surfaces, providing very high exchange area to
contact the
impurity-containing stream. Other microchannels can be provided for flow of
heat transfer
fluid for precise temperature control of the device to efficiently regulate
and cycle between
the adsorption and desorption steps.
Separation processes, such as distillation, stripping, extraction, and
adsorption, based
on microchannel technology provide the enhanced heat and mass transfer
required to achieve
ultra pure products (ppm, ppb). These separation processes additionally
provide the
CA 02727510 2011-01-12
21
intensification of transfer stages needed to solve the problem of separating
fluid mixtures
with similar boiling points (relative volatility, 0.8 < a < 1.5) to high
purity levels.
Advantageous operating conditions include temperatures and pressures where one
or more of
the fluid components is in the liquid phase and capable of undergoing a phase
change either
to the vapor state or to an adsorbed state on a sorbent. This can include
temperatures from -
25 C to 250 C, and pressures from 0.1 Pa to 10 MPa. Feed impurity levels can
range from
1 ppm up to 10 wt% or even 50 wt% of the fluid mixture.
The organometallic compounds of the present invention are particularly
suitable for
use as precursors in all vapor deposition methods such as LPE, MBE, CBE, ALD,
CVD,
MOCVD and MOVPE. The present compounds are useful for depositing films
containing
one or more of Group IV, Group VI or both Group IV and Group VI metals. Such
films are
useful in the manufacture of electronic devices, such as, but not limited to,
integrated circuits,
optoclectronic devices and light emitting diodes.
Films of Group IV and/or Group VI metals are typically deposited by first
placing the
desired alkylmetal compound, i.e. source compound or precursor compound, in a
delivery
device, such as a cylinder, having an outlet connected to a deposition
chamber. A wide
variety of cylinders may be used, depending upon the particular deposition
apparatus used.
When the precursor compound is a solid, the cylinders disclosed in U.S. Pat.
No. 6,444,038
(Rangarajan et al.) and U.S. Pat. No. 6,607,785 (Timmons et al.), as well as
other designs,
may be used. For liquid precursor compounds, the cylinders disclosed in U.S.
Pat. No.
4,506,815 (Melas et al.) and U.S. Pat. No. 5,755,885 (Mikoshiba et al.) may be
used, as well
as other liquid precursor cylinders. The source compound is maintained in the
cylinder as a
liquid or solid. Solid source compounds are typically vaporized or sublimed
prior to
transportation to the deposition chamber.
The source compound is typically transported to the deposition chamber by
passing a
carrier gas through the cylinder. Suitable carrier gasses include nitrogen,
hydrogen, and
mixtures thereof. In general, the carrier gas is introduced below the surface
of the source
compound, and passes up through the source compound to the headspace above it,
entraining
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or carrying vapor of the source compound in the carrier gas. The entrained or
carried vapor
then passes into the deposition chamber.
The deposition chamber is typically a heated vessel within which is disposed
at least
one, and possibly many, substrates. The deposition chamber has an outlet,
which is typically
connected to a vacuum pump in order to draw by-products out of the chamber and
to provide
a reduced pressure where that is appropriate. MOCVD can be conducted at
atmospheric or
reduced pressure. The deposition chamber is maintained at a temperature
sufficiently high to
induce decomposition of the source compound. The deposition chamber
temperature is from
200 to 1200 C, the exact temperature selected being optimized to provide
efficient
deposition. Optionally, the temperature in the deposition chamber as a whole
can be reduced
if the substrate is maintained at an elevated temperature, or if other energy
such as radio
frequency ("RF") energy is generated by an RF source.
Suitable substrates for deposition, in the case of electronic device
manufacture, may
be silicon, gallium arsenide, indium phosphide, and the like. Such substrates
may contain one
or more additional layers of materials, such as, but not limited to,
dielectric layers and
conductive layers such as metals. Such substrates are particularly useful in
the manufacture
of integrated circuits, opotoelectronic devices and light emitting diodes.
Deposition is continued for as long as desired to produce a film having the
desired
properties. Typically, the film thickness will be from several hundred
angstroms to several
tens of nanometers to several hundreds of microns or more when deposition is
stopped.
The following examples are expected to further illustrate various aspects of
the
present invention, but are not intended to limit the scope of the invention in
any aspect. All
manipulations are performed in an inert atmosphere, typically under an
atmosphere of dry
nitrogen.
CA 02727510 2011-01-12
23
EXAMPLES
Comparative Example #1
Tetramethylgermane was synthesized according to the following equation:
GeCl4+ 2(CH3)3Al.Pr3N.- (CH3)4Ge + 2CH3AIC12.Pr3N
To 150 g of high boiling linear alkylbenzenes was added under nitrogen
trimethylaluminum (40 g, 0.554 moles) in a 3-necked round-bottomed flask. To
this was
added n-propylamine (79.5 g, 0.554 moles) dropwise at room temperature. The
addition
lasted 30 minutes during which period the mixture became warm (ca. 50 C).
After the
addition was complete and the mixture was allowed to cool to room temperature,
neat
germanium chloride (40 g, 0.186 moles) was added dropwise at room temperature
to the
adduct formed. The addition took 1 hour during which time the reaction mixture
warmed
again to ca. 60 C. After cooling to room temperature, the reaction mass was
heated to 160 to
170 C. (oil bath temperature) during which time 20 g of crude product,
tetramethylgermane,
distilled through a U-tube into a dry ice cooled receiver. The identity of the
product was
confirmed by 'H nmr (--CH3 resonance at 0.1 ppm) and showed it to contain some
tripropyl
amine (<5%). Yield of crude product was 81.6%. 'H nmr analysis of the
remaining pot
residues indicated the presence of more tetramethylgermane that was not
isolated.
EXAMPLE 1
Tetramethylgermane is synthesized according to the following equation.
GeCl4+ 2 (CH3)3AIPr3N (CH3)4Ge + 2 CH3AICI2Pr3N
An equimolar solution of trimethylaluminum and n-propylamine is made in a high
boiling linear alkylbenzenes solvent under nitrogen. The trimethylaluminum/n-
propylamine
solution and neat germanium chloride are added continuously at room
temperature to the
microchannel device. The microchannel device provides separate flow paths for
the reagents
CA 02727510 2011-01-12
24
and the said flow paths communicate with each other in a mixing region in
which the
reagents contact each other, The reagent flows are controlled to maintain a
molar ratio of
trimethylaluminum to germanium chloride of 3. The mixture enters a reaction
region in the
microchannel device leading to alkylation occurring between the reagents. The
said reaction
region has a width perpendicular to the direction of flow in the range of Ito
100
micrometers. The said reaction region has a length (in the direction of the
flow) in the range
I micrometer to I meter, the optimum length to be determined by the kinetics
of the
alkylation reaction to achieve an adequate residence time (1 second to 10
minutes) that is set
by adjusting the flow rates and to offer at least 80% conversion. The
temperature of the
reaction is controlled to within +/- 1 C by the flow of a heat transfer
fluid, such as
Therminol, in separate flow channels to the reaction channels within the
microchannel
device. The reaction product stream exits the microchannel reactor and is
collected and
distilled at 160-170 C to yield the desired Me4Ge product. The purity of the
Me4Ge product
as measured by FT-NMR and ICP-AES is expected to be 99.9999% pure.
EXAMPLE 2
High purity trimethylaluminum-tripropylamine adduct was synthesized using
microchannel device according to the following equation.
(CH3)3A1 + Pr3N (CH3)3A1.Pr3N Adduct
The microchannel reactor comprising multiple, parallel channels constructed of
316
SS with cross-sectional dimensions of approximately I x 3 mm and length
greater than 1 in
was used in preparation of purified organoaluminum - tertiary amine adduct.
Each channel of
microchannel device was in contact with heat exchange zones. A feedstream of
trimethylaluminum (TMA) at room temperature containing 31.6 ppm Si (as
detected by ICP
technique) was fed to the continuous flow reactor at 2.5 kg/hr. A feedstream
of
tripropylamine at room temperature was co-fed to the reactor through a
separate injection
port at 5.0 kg/hr. The two feeds were internally mixed in the flow channels.
Reactor
temperature was controlled using cooling oil (40 C) circulated to the reactor
heat exchange
CA 02727510 2011-01-12
channels to maintain a steady process outlet temperature of -50 C. The
reactor effluent (7.5
kg/hr) was fed to a continuous thin film evaporator to purify the adduct. The
evaporator
surface was continuously wiped by a rotating blade and operated at 2 torr and
a jacket
temperature of 80 C. The purified TMA:Adduct was collected in greater than 98
wt% yield
and sampled for analysis. The ICP analysis showed the product to have
significantly reduced
silicon impurity than the starting material, as shown by Si = 0.7 ppm reduced
from 31.6 ppm.
