U.S. patent application number 15/274997 was filed with the patent office on 2017-03-16 for group 11 mono-metallic precursor compounds and use thereof in metal deposition.
The applicant listed for this patent is Greencentre Canada. Invention is credited to Sean BARRY, Timothy James CLARK, Jason COYLE, Jeffrey J.M. HASTIE.
Application Number | 20170073361 15/274997 |
Document ID | / |
Family ID | 47176095 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170073361 |
Kind Code |
A1 |
BARRY; Sean ; et
al. |
March 16, 2017 |
GROUP 11 MONO-METALLIC PRECURSOR COMPOUNDS AND USE THEREOF IN METAL
DEPOSITION
Abstract
The present application provides precursor compounds useful for
deposition of a group 11 metal on a substrate, for example, a
microelectronic device substrate, as well as methods of
synthesizing such precursor compounds. The precursor compounds
provided are mono-metallic compounds comprising a diaminocarbene
(DAC) having the general formula: "DAC-M-X", where the
diaminocarbene is an optionally substituted, saturated
N-heterocyclic diaminocarbene (sNHC) or an optionally substituted
acyclic diaminocarbene, M is a group 11 metal, such as copper,
silver or gold; and X is an anionic ligand. Also provided are
methods of synthesizing the precursor compounds, metal deposition
methods utilizing such precursor compounds, and to composite
materials, such as, e.g., microelectronic device structures, and
products formed by use of such precursors and deposition
methods.
Inventors: |
BARRY; Sean; (Ottawa,
CA) ; COYLE; Jason; (Ottawa, CA) ; CLARK;
Timothy James; (Kingston, CA) ; HASTIE; Jeffrey
J.M.; (Kingston, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Greencentre Canada |
Kingston |
|
CA |
|
|
Family ID: |
47176095 |
Appl. No.: |
15/274997 |
Filed: |
September 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13468601 |
May 10, 2012 |
9453036 |
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15274997 |
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PCT/CA2012/005096 |
May 4, 2012 |
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13468601 |
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61485912 |
May 13, 2011 |
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61552169 |
Oct 27, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 5/24 20130101; H01L
21/32051 20130101; C07F 7/10 20130101; C07F 1/00 20130101; C07F
1/08 20130101; C23C 16/45553 20130101; C07F 1/005 20130101; C23C
16/18 20130101; C23C 16/50 20130101 |
International
Class: |
C07F 7/10 20060101
C07F007/10; C07F 1/08 20060101 C07F001/08; C23C 16/50 20060101
C23C016/50; H01L 21/3205 20060101 H01L021/3205; C23C 16/18 20060101
C23C016/18; C23C 16/455 20060101 C23C016/455; C09D 5/24 20060101
C09D005/24; C07F 1/00 20060101 C07F001/00 |
Claims
1. A compound of Formula I: DAC-M-X I wherein DAC is a
diaminocarbene that is an optionally substituted, saturated
N-heterocyclic diaminocarbene (sNHC) or an optionally substituted
acyclic diaminocarbene; M is a transition metal bound to the DAC
component at the carbenic atom; and X is an anionic ligand, wherein
the compound does not comprise an aryl or heteroaryl group, and M
is bound to a non-halogenic atom of X, and wherein the compound
will achieve a vapour pressure of at least about 1 torr at
160.degree. C. or less and will remain stable for at least one day
at a temperature of at least about 100.degree. C.
2. The compound of claim 1, wherein M is a group 11 metal.
3. The compound of claim 1, which is a compound of Formula Ia:
sNHC-M-X Ia.
4. The compound of claim 3, which is a compound of Formula IIa:
##STR00032## wherein Y is CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2,
or NR.sup.9; R.sup.1 and R.sup.2 are each independently H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent; R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each
independently H, or an optionally substituted, branched, straight
or cyclic aliphatic group; and R.sup.9 is H, or an optionally
substituted, branched, straight or cyclic aliphatic group.
5. The compound of claim 1, which is a compound of Formula IIb
##STR00033## wherein each R.sup.1 and R.sup.2 is independently H,
or an optionally substituted, branched, straight or cyclic
aliphatic group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent.
6. The compound of claim 1, wherein X is not bound to M via an
oxygen-metal bond.
7. The compound of claim 1, wherein X is heterocycle, piperidinyl,
pyrrolidinyl, alkoxide, alkyl, hydride, hydroxide, diketonate,
diketiminate, amidinate or guanidinate or is an amide having the
following structure: ##STR00034## where R.sup.7 and R.sup.8 are
each independently an optionally substituted branched, straight or
cyclic aliphatic group, an optionally substituted branched or
straight C.sub.1 to C.sub.12 alkylsilyl, or R.sup.7 and R.sup.8
together with the amide nitrogen form an optionally substituted
heterocycle.
8. The compound of claim 7, wherein R.sup.7 and R.sup.8 are each
independently H, a C.sub.1 to C.sub.12 alkyl or heteroalkyl, or a
C.sub.3 to C.sub.12 cycloalkyl or cyclic heteroalkyl.
9. The compound of claim 8, wherein X is --N(SiMe.sub.3).sub.2.
10. The compound of claim 4, wherein R.sup.1, R.sup.2, R.sup.3,
R.sup.4, R.sup.5 and R.sup.6 are each independently H, a C.sub.1 to
C.sub.12 alkyl, or heteroalkyl or a C.sub.3 to C.sub.12 cycloalkyl
or cyclic heteroalkyl.
11. The compound of claim 4, wherein R.sup.1, R.sup.2, R.sup.3,
R.sup.4, R.sup.5 and R.sup.6 are each independently H, a C.sub.1 to
C.sub.6 alkyl or heteroalkyl, or a C.sub.3 to C.sub.8 cycloalkyl or
cyclic heteroalkyl.
12. The compound of claim 11, wherein R.sup.1 and R.sup.2 are each
independently methyl, ethyl, propyl, isopropyl, butyl,
1-methylpropyl, or t-butyl.
13. The compound of claim 1, wherein M is copper, silver, or
gold.
14. The compound of claim 1, which is: ##STR00035## ##STR00036##
##STR00037##
15. The compound of claim 4, which is
1,3-diisopropyl-imidazolin-2-ylidene copper
hexamethyldisilazide.
16. (canceled)
17. The compound of claim 1, wherein the compound remains stable at
a temperature of at least about 150.degree. C. for an extended
period.
18. The compound of claim 1, which is at least 95% pure.
19. The compound of claim 1, which is at least 98% pure.
20. A process for depositing a metal film on a substrate,
comprising chemical vapour deposition (CVD), atomic layer
deposition (ALD), plasma enhanced chemical vapour deposition
(PE-CVD) or plasma enhanced atomic layer deposition (PE-ALD) using
a compound of claim 1, wherein M is a group 11 metal, as a
precursor compound.
21. A process for forming a thin film comprising a metal, said
process comprising the following step: (a) exposing a substrate to
vapour comprising a precursor compound of Formula I: DAC-M-X I
wherein DAC is a diaminocarbene that is an optionally substituted,
saturated N-heterocyclic diaminocarbene (sNHC) or an optionally
substituted acyclic diaminocarbene; M is a group 11 metal bound to
the sNHC component at the carbenic atom; and X is an anionic
ligand, and wherein the precursor compound does not comprise an
aryl or heteroaryl group, and M is bound to a non-halogenic atom of
X.
22. (canceled)
23. (canceled)
24. The process of claim 21, wherein in the step of exposing a
substrate to vapour comprising a precursor compound, the substrate
is exposed to a vapour comprising the precursor compound and a
reactive gas to form a metal film on the surface of the
substrate.
25. The process of claim 21 additionally comprising: volatilizing
the precursor compound to form a precursor vapour prior to exposing
the substrate to the precursor vapour.
26. The process of claim 21, wherein the precursor compound is: a
compound of Formula Ia: sNHC-M-X Ia; or a compound of Formula IIa:
##STR00038## wherein Y is CR5R6, (CR5R6)2, or NR9; R.sup.1 and
R.sup.2 are each independently H, or an optionally substituted,
branched, straight or cyclic aliphatic group, wherein R.sup.1 and
R.sup.2 do not comprise a halo substituent; R.sup.3, R.sup.4,
R.sup.5 and R.sup.6 are each independently H, or an optionally
substituted, branched, straight or cyclic aliphatic group; and
R.sup.9 is H, or an optionally substituted, branched, straight or
cyclic aliphatic group; or a compound of Formula IIb: ##STR00039##
wherein each R.sup.1 and R.sup.2 is independently H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent
27.-29. (canceled)
30. The process of claim 21, wherein the temperature of
vaporization of the compound is above 50.degree. C.
31. The process of claim 21, further comprising heating the
substrate.
32. The process of claim 21, wherein the substrate comprises:
glass; TaN; TiN; sapphire; indium tin oxide (ITO); SiO.sub.2;
silicon; silicon nitride; silicon oxy nitride; silicon oxycarbide;
fused silica; polymeric material; tungsten; tantalum; ruthenium;
organic materials; another metal or alloy used as a barrier layer
in semiconductor manufacturing; or any combination thereof.
33. The process of claim 21, wherein M is Cu, Ag, or Au.
34. A system for use in metal deposition to form a thin film on a
substrate, comprising a precursor compound according to claim 1,
wherein M is a group 11 metal.
35. The system of claim 34, wherein said precursor compound is in
an air-tight container.
36. The system of claim 35, wherein said air-tight container is a
bubbler configured for use with an ALD tool, a flame sealed ampule,
or a vial or tube having a cap that is removably attached to said
vial or tube to produce an air-tight seal.
37. (canceled)
38. The system claim 34, wherein the precursor compound is packaged
under an inert atmosphere.
39. (canceled)
40. The system of claim 34, additionally comprising a desiccant, an
anti-oxidant or an additive for inhibiting spontaneous
decomposition of said precursor compound.
41. The system of claim 34, additionally comprising means for
volatilizing said precursor compound.
42. The system of claim 41, wherein said means for volatilizing
said precursor compound is comprised within an atomic layer
deposition (ALD) or chemical vapour deposition (CVD) tool.
43. An atomic layer deposition (ALD) precursor formulation
comprising a mono-metallic precursor compound of claim 1, wherein M
is a group 11 metal.
44. The ALD precursor formulation of claim 43, packaged in an
air-tight container under an inert atmosphere.
45. (canceled)
46. A method of synthesizing a metal precursor compound of Formula
Ia DAC-M-X Ia wherein DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; M is a metal bound
to the sNHC component at the carbenic atom; and X is an anionic
ligand, and wherein DAC and X do not comprise an aryl or heteroaryl
group, said method comprising: reacting an DAC metal halide with a
salt of the anionic ligand such that a bond is formed between M and
a non-halogenic atom of X.
47. The method of claim 46, wherein M is a group 11 metal.
48. The method of claim 46, comprising reacting a metal halide of
Formula IV: ##STR00040## wherein B is a halide; Y is
CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or NR.sup.5; R.sup.1 and
R.sup.2 are each independently H, or an optionally substituted
branched, straight or cyclic aliphatic group, wherein R.sup.1 and
R.sup.2 do not comprise any halide atoms; and R.sup.3, R.sup.4,
R.sup.5 and R.sup.6 are each independently H, or an optionally
substituted, branched, straight or cyclic aliphatic group; with a
salt of the anionic ligand X to produce a compound of Formula IIa:
##STR00041## wherein the precursor compound does not comprise an
aryl or heteroaryl group, and M is bound to a non-halogenic atom of
X.
49. The method of claim 46, comprising reacting a metal halide of
Formula IVb: ##STR00042## wherein B is a halide; Y is
CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or NR.sup.5; R.sup.1 and
R.sup.2 are each independently H, or an optionally substituted
branched, straight or cyclic aliphatic group, wherein R.sup.1 and
R.sup.2 do not comprise any halide atoms; and R.sup.3, R.sup.4,
R.sup.5 and R.sup.6 are each independently H, or an optionally
substituted, branched, straight or cyclic aliphatic group; with a
salt of the anionic ligand X to produce a compound of Formula IIb:
##STR00043## wherein the precursor compound does not comprise an
aryl or heteroaryl group, and M is bound to a non-halogenic atom of
X.
53. The process of claim 21, wherein the process is carried out
under conditions that permit adsorption of the precursor compound
to form a monolayer on the substrate and the process additionally
comprises: (b) purging excess precursor compound; (c) exposing the
adsorbed precursor monolayer formed in step (a) to a reactant
precursor compound to reduce the precursor monolayer to form a
metal layer; and (d) repeating steps (a)-(c) until the thin film
reaches a desired thickness.
54. The process of claim 53, wherein the reactant precursor is:
plasma; an oxidizing gas, such as oxygen, ozone, water, hydrogen
peroxide, nitric oxide, nitrogen dioxide, a radical species
thereof, or a mixture of any two or more of the oxidizing gases; or
a reducing agent such as one of hydrogen, a forming gas (i.e.,
.about.5% hydrogen, .about.95% nitrogen mixture), ammonia, a
silane, a borane, an amino borane, an alane, formic acid, a
hydrazine (e.g., dimethylhydrazine), a radical species thereof, or
a mixture of any two or more of the reducing agents.
55. The compound of claim 1, wherein M is a metal selected from the
group consisting of Groups 4, 5, 6, 7, and 11 of the periodic
table.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to precursor compounds useful
for deposition of a group 11 metal on a substrate, for example, a
microelectronic device substrate, as well as to methods of
synthesizing such precursor compounds and to corresponding
deposition methods of utilizing such precursors, and to composite
materials, such as, microelectronic device structures, and products
formed by use of such precursors and deposition methods, also
including specialty optics, thin-films in batteries and other
applications, sensors, catalyst substrates, and other surfaces
requiring fine coatings.
BACKGROUND OF THE INVENTION
[0002] Microfabrication processes are used in the fabrication of
structures of micrometre sizes and smaller. The earliest
microfabrication processes were used for integrated circuit
manufacture (or semiconductor device fabrication), however,
recently these processes have been applied, for example, in
microelectromechanical systems (MEMS) and subfields, such as
microfluidics/lab-on-a-chip, optical MEMS, etc. The miniaturization
of devices presents challenges in fabrication technologies.
[0003] While microfabrication is a collection of technologies used
in manufacturing micro- and nanodevices, most microfabrication
processes include thin film deposition. The purpose and material
used in these thin films varies depending on the type of device.
Commonly, electronic devices require thin films which are
conductors (metal).
[0004] Copper is often used in semiconductor device manufacturing.
As the use of copper has permeated the marketplace because of its
relatively low cost and processing properties, semiconductor
manufacturers continue to look for ways to improve copper
deposition techniques. Several processing methods have been
developed to manufacture copper interconnects as feature sizes have
decreased. Each processing method may increase the likelihood of
errors such as copper diffusion across boundary regions, copper
crystalline structure deformation, and dewetting. Physical vapour
deposition (PVD), chemical vapour deposition (CVD), atomic layer
deposition (ALD), chemical mechanical polishing (CMP),
electrochemical plating (ECP), electrochemical mechanical polishing
(ECMP), and other methods of depositing and removing copper layers
utilize mechanical, electrical, or chemical methods to manipulate
the copper that forms the interconnects.
[0005] Physical vapour deposition (PVD) or sputtering has been
adopted as a preferred method for depositing conductor films used
in semiconductor manufacturing. This has been primarily driven by
the low cost, simple sputtering approach of PVD whereby relatively
pure elemental or compound materials can be deposited at relatively
low substrate temperatures. However, as device length scales have
decreased, the step coverage limitations of PVD have increasingly
become an issue since it is inherently a line-of-sight process.
Step coverage refers to the difference in deposited film thickness
in different parts of a micro- or nanostructure. Ideally, there is
no difference in deposited film thickness throughout the structure.
This is difficult or impossible to achieve using a line-of-sight
process such as PVD, which limits the total number of atoms or
molecules that can be delivered into a trench or via (resulting in
thinner films in trenches or vias than in the rest of the
structure). Consequently, PVD is unable to deposit thin continuous
films of adequate thickness to coat the sides and bottoms of high
aspect ratio trenches and vias.
[0006] In addition, miniaturization of devices has led to a desire
for thinner seed layers, which require greater flatness and
uniformity in order to plate evenly. Copper resistivity increases
sharply in films less than 10 nm in thickness, leading to uneven
plating. Medium/high-density plasma and ionized PVD sources have
been developed in an attempt to provide film uniformity even in the
more aggressive device structures. However, these sources are still
not adequate and are now of such complexity that cost and
reliability have become serious concerns.
[0007] CVD processes offer improved step coverage (i.e., improved
film uniformity) since CVD processes can be tailored to provide
conformal films. Conformality ensures the deposited films match the
shape of the underlying substrate, and the film thickness inside
the feature, such as a trench or via, is uniform and equivalent to
the thickness outside the feature. Unfortunately, CVD requires
comparatively high deposition temperatures, suffers from high
impurity concentrations, which impact film integrity, and is more
expensive than PVD due to long nucleation times and poor precursor
gas utilization efficiency.
[0008] Atomic layer deposition (ALD) has been proposed as an
alternative method to CVD for depositing conformal, ultra-thin
films at comparatively lower temperatures. ALD is similar to CVD
except that the substrate is sequentially exposed to one reactant
at a time, or one dose of a reactant at a time. Conceptually, it is
a simple process: a first reactant is introduced to a heated
substrate whereby it forms a monolayer on the surface of the
substrate. Excess reactant is pumped out (e.g., evacuated). Next a
second reactant is introduced and reacts with the existing
monolayer to form a monolayer of a desired reaction product through
a "self-limiting surface reaction". The process is self-limiting
since the deposition reaction halts once the initially adsorbed
(physisorbed or chemisorbed) monolayer of the first reactant has
fully reacted with the second reactant. Finally, the excess second
reactant is evacuated. This sequence comprises one deposition
cycle. The desired film thickness is obtained by repeating
deposition cycles as necessary to reach the desired film thickness.
As is apparent, the sequential nature of ALD precursor deposition,
reaction and alternate purging one atomic/molecular layer at a time
has the disadvantage of being slower than some other deposition
techniques. However it is this cycle of building up highly uniform
monolayers one at a time that allows ALD to produce films of a
surface uniformity, smoothness and thinness that is impossible to
achieve with other techniques. This makes ALD uniquely valuable in
demanding coating applications.
[0009] In practice, ALD is complicated by painstaking process
optimisation wherein: 1) at least one of the reactants sufficiently
adsorbs to a monolayer and 2) surface deposition reaction can occur
with adequate growth rate and film purity. If the substrate
temperature needed for the deposition reaction is too high,
desorption or decomposition of the first adsorbed reactant occurs,
thereby preventing the layer-by-layer growth process. High
substrate temperatures can also lead to mobility of the coating
material which may agglomerate and ruin the film flatness or the
coating material can become less uniformly dispersed or become
dewetted, especially at boundary regions of a substrate structure.
If the temperature is too low, the deposition reaction may be
incomplete (i.e., very slow), not occur at all, or lead to poor
film quality (e.g., high resistivity in the case of metals and/or
high impurity content). Low temperatures may also give rise to
insufficient activation of the precursor to form a monolayer, or
condensation of a multilayer of precursor molecules. Since ALD
processes largely rely on the thermal reactivity of precursors
(i.e., reactants), selection of those that fit this temperature
window becomes difficult and sometimes unattainable. Due to the
strict process optimisation requirements, ALD has been typically
limited to the deposition of semiconducting or insulating materials
as opposed to metals. Until recently ALD of metals has been
confined to the use of metal halide precursors. However, halides
(e.g., Cl, F, Br) are corrosive and can create reliability issues
in metal interconnects.
[0010] As a result of its low resistivity, low contact resistance,
and ability to enhance device performance through the reduction of
resistor-capacitor time delays, copper metallization has been
adopted by many semiconductor device manufacturers for production
of microelectronic chips, thin-film recording heads and packaging
components.
[0011] There remains a need for precursors of copper and other
metals that have sufficient volatility and thermal stability to be
useful in ALD.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide group 11
mono-metallic precursor compounds and methods and systems of use
thereof in metal deposition and methods of synthesis thereof.
[0013] In accordance with one aspect, there is provided a compound
of Formula I:
DAC-M-X I
[0014] wherein [0015] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0016] M is a metal,
for example a group 11 metal, bound to the DAC component at the
carbenic atom; and [0017] X is an anionic ligand,
[0018] and wherein DAC and X do not comprise an aryl or heteroaryl
group, and M is bound to a non-halogenic atom of X.
[0019] In accordance with one embodiment, there is provided a
compound of Formula Ia:
sNHC-M-X Ia
[0020] wherein [0021] sNHC is a saturated N-heterocyclic
diaminocarbene that is optionally substituted; and M and X are as
defined above, [0022] and wherein the compound does not comprise an
aryl or heteroaryl group, and M is bound to a non-halogenic atom of
X.
[0023] In an alternative embodiment, the DAC is an acyclic
diaminocarbene; and M and X are as defined above.
[0024] In accordance with another aspect, there is provided a
compound of Formula IIa:
##STR00001##
[0025] wherein [0026] X is an anionic ligand; [0027] M is a metal,
for example a group 11 metal, such as, copper, silver or gold;
[0028] Y is CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or NR.sup.9;
[0029] R.sup.1 and R.sup.2 are each independently H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent; [0030] R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each
independently H, or an optionally substituted, branched, straight
or cyclic aliphatic group; and [0031] R.sup.9 is absent or H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein, when R.sup.9 is absent, the bond between N and the
adjacent C is a double bond and R.sup.3 or R.sup.4 is absent,
[0032] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
[0033] In accordance with certain embodiments, an aliphatic group
is a C.sub.1 to C.sub.12 alkyl or heteroalkyl or a C.sub.3 to
C.sub.12 cycloalkyl or cyclic heteroalkyl.
[0034] In accordance with another aspect, there is provided a
compound of Formula IIb:
##STR00002##
[0035] wherein [0036] X is an anionic ligand; [0037] M is a metal,
for example, a group 11 metal, such as, copper, silver or gold; and
[0038] each R.sup.1 and R.sup.2 is independently H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent, [0039] and wherein the compound does not comprise an
aryl or heteroaryl group and M is bound to a non-halogenic atom of
X.
[0040] It should be understood that in the compound of Formula IIb,
the two R.sup.1 substituents can be different from one another and
from each of the two R.sup.2 substituents. Similarly, it should be
understood that the two R.sup.2 substituents can be different from
one another and from each of the two R.sup.1 substituents.
Specifically, the structure of Formula IIb encompasses compounds
having four different substituents at the two nitrogens.
[0041] A process for depositing a metal film on a substrate,
comprising chemical vapour deposition (CVD), atomic layer
deposition (ALD), plasma enhanced chemical vapour deposition
(PE-CVD) or plasma enhanced atomic layer deposition (PE-ALD) using
a compound of Formula I:
DAC-M-X I
[0042] wherein [0043] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0044] M is a group
11 metal, such as copper, silver or gold, bound to the DAC
component at the carbenic atom; and [0045] X is an anionic ligand,
and wherein DAC and X do not comprise an aryl or heteroaryl group,
and M is bound to a non-halogenic atom of X.
[0046] In accordance with another aspect, there is provided a
process for forming a thin film comprising a metal, said process
comprising the steps: exposing a substrate to vapour comprising a
precursor compound of Formula I:
DAC-M-X I
[0047] wherein [0048] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0049] M is a group
11 metal bound to the sNHC component at the carbenic atom; and
[0050] X is an anionic ligand,
[0051] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X,
under conditions that permit adsorption of the precursor compound
to form a monolayer on the substrate; purging excess precursor
compound; exposing the adsorbed precursor monolayer formed in the
first step to a second precursor compound to reduce the precursor
monolayer to form a metal layer; and repeating the steps until the
thin film reaches a desired thickness.
[0052] In accordance with another aspect, there is provided a
process for forming a thin film comprising a metal, comprising:
exposing a substrate to vapour comprising a precursor compound and
a reactive gas to form a metal film on the surface of the
substrate, wherein the precursor compound is a compound of Formula
I:
DAC-M-X I
[0053] wherein [0054] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0055] M is a group
11 metal bound to the sNHC component at the carbenic atom; and
[0056] X is an anionic ligand,
[0057] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
Optionally, the precursor and the reactive gas are introduced in a
stepwise process. In one embodiment of the present invention, the
reactive gas is plasma.
[0058] In accordance with another aspect, there is provided a
process for forming a group 11 metal-containing film on a substrate
comprising: volatilizing a group 11 mono-metallic precursor
compound to form a precursor vapour; and contacting the substrate
with the precursor vapour to form the group 11 metal-containing
film on said substrate,
[0059] wherein the precursor is a compound of Formula I:
DAC-M-X I
[0060] wherein [0061] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0062] M is a group
11 metal bound to the sNHC component at the carbenic atom; and
[0063] X is an anionic ligand,
[0064] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
[0065] In accordance with another aspect, there is provided a
system for use in metal deposition to form a thin film on a
substrate, comprising a compound of Formula I:
DAC-M-X I
[0066] wherein [0067] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0068] M is a group
11 metal bound to the sNHC component at the carbenic atom; and
[0069] X is an anionic ligand,
[0070] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
[0071] In accordance with another aspect, there is provided an ALD
precursor formulation comprising a group 11 mono-metallic precursor
compound of Formula I:
DAC-M-X I
[0072] wherein [0073] DAC is a diaminocarbene that is an optionally
substituted, saturated N-heterocyclic diaminocarbene (sNHC) or an
optionally substituted acyclic diaminocarbene; [0074] M is a group
11 metal bound to the sNHC component at the carbenic atom; and
[0075] X is an anionic ligand,
[0076] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
[0077] In accordance with another aspect, there is provided a
method of synthesizing a metal precursor compound of Formula Ia
sNHC-M-X Ia
[0078] wherein [0079] sNHC is a saturated N-heterocyclic
diaminocarbene that is optionally substituted; [0080] M is a metal,
for example, a group 11 metal, bound to the sNHC component at the
carbenic atom; and [0081] X is an anionic ligand, said method
comprising:
[0082] reacting an sNHC metal halide with a salt of the anionic
ligand such that a bond is formed between M and a non-halogenic
atom of X.
[0083] In accordance with one embodiment, the method of synthesis
comprises reacting a metal halide of Formula IV or Formula IVa:
##STR00003##
[0084] wherein B is a halide; [0085] M is a metal, for example a
group 11 metal, such as, copper, silver or gold; [0086] Y is
CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or NR.sup.5; [0087]
R.sup.1 and R.sup.2 are each independently H, or an optionally
substituted branched, straight or cyclic aliphatic group, wherein
R.sup.1 and R.sup.2 do not comprise any halide atoms; and [0088]
R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently H, or
an optionally substituted, branched, straight or cyclic aliphatic
group; with a salt of the anionic ligand X to produce a compound of
Formula IIa or Formula IIb, respectively:
##STR00004##
[0089] wherein the precursor compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X.
[0090] It should be understood that the two R.sup.1 substituents
can be different from one another and from each of the two R.sup.2
substituents. Similarly, it should be understood that the two
R.sup.2 substituents can be different from one another and from
each of the two R.sup.1 substituents. Specifically, the structure
of Formula IVa encompasses compounds having four different
substituents at the two nitrogens.
BRIEF DESCRIPTION OF THE DRAWINGS
[0091] For a better understanding of the present invention, as well
as other aspects and further features thereof, reference is made to
the following description which is to be used in conjunction with
the accompanying drawings, where:
[0092] FIG. 1 is a pictorial overview of an atomic layer deposition
process;
[0093] FIG. 2 is a schematic representation of a step in plasma ALD
in which a second precursor/reactant is introduced to reduce the
surface monolayer;
[0094] FIG. 3 is an ORTEP drawing of the X-ray crystal structure of
1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper
hexamethyldisilazide;
[0095] FIGS. 4-6 are depictions of sublimation apparatuses;
[0096] FIG. 7 is an ORTEP drawing of the X-ray crystal structure of
1,3-diisopropyl-imidazolin-2-ylidene gold hexamethyldisilazide
(2c);
[0097] FIG. 8 is a graph of vapour pressure plots for four
symmetrical copper precursor compounds in comparison to a control
(copper bis-(2,2,6,6-tetramethyl-3,5-heptadionate);
[0098] FIG. 9 is a graph of vapour pressure plots for three
asymmetrical copper precursor compounds in comparison to a control
(copper bis-(2,2,6,6-tetramethyl-3,5-heptadionate);
[0099] FIG. 10 is a weight loss curve for an unsaturated
N-heterocyclic diaminocarbene-containing copper compound
(1,3-di-tert-butyl-imidazol-2-ylidene copper
hexamethyldisilazide);
[0100] FIG. 11 is a weight loss curve for an unsaturated
N-heterocyclic diaminocarbene-containing copper compound
(1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper
hexamethyldisilazide);
[0101] FIG. 12 is a weight loss curve for
1,3-diethyl-imidazolin-2-ylidene copper hexamethyldisilazide
(1a);
[0102] FIG. 13 is a weight loss curve for
1,3-diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide
(2a);
[0103] FIG. 14 is a weight loss curve for
1,3-di-tert-butyl-imidazolin-2-ylidene copper hexamethyldisilazide
(3a);
[0104] FIG. 15 is a weight loss curve for
1,3-di-tert-butyl-4,5-dimethyl-imidazolin-2-ylidene copper
hexamethyldisilazide (4a);
[0105] FIG. 16 is a weight loss curve for
1-tert-butyl-3-ethyl-imidazolin-2-ylidene copper
hexamethyldisilazide (13a);
[0106] FIG. 17 is a weight loss curve for
1-tert-butyl-3-isopropyl-imidazolin-2-ylidene copper
hexamethyldisilazide (14a);
[0107] FIG. 18 is a weight loss curve for
1-tert-butyl-3-methyl-imidazolin-2-ylidene copper
hexamethyldisilazide (12a);
[0108] FIG. 19 is a weight loss curve for
1,3-disopropyl-imidazolin-2-ylidene silver hexamethyldisilazide
(2b);
[0109] FIG. 20A is a weight loss curve from an isotherm study using
1,3-disopropyl-imidazolin-2-ylidene silver hexamethyldisilazide
(2b);
[0110] FIG. 20B is a weight loss curve from an isotherm study using
1,3-disopropyl-imidazolin-2-ylidene gold hexamethyldisilazide
(2c);
[0111] FIG. 21 is a weight loss curve for
1,3-disopropyl-imidazolin-2-ylidene gold hexamethyldisilazide
(2c);
[0112] FIG. 22 is a metal deposition saturation curve obtained
using 1,3-diisopropyl-imidazolin-2-ylidene copper
hexamethyldisilazide (2a) as a precursor in ALD;
[0113] FIG. 23 is an electron micrograph of the thickest film
profile of the film produced in obtaining the saturation curve of
FIG. 22;
[0114] FIGS. 24 and 25 are electron micrographs of the 0 .ANG. film
produced at point 2 of the saturation curve of FIG. 22;
[0115] FIGS. 26 and 27 are electron micrographs of the
approximately 141 .ANG. film produced at point 4 of the saturation
curve of FIG. 22;
[0116] FIGS. 28 and 29 are electron micrographs of the
approximately 350 .ANG. film produced at point 6 of the saturation
curve of FIG. 22;
[0117] FIGS. 30A and B are photographs of NMR tubes showing copper
deposition from mono-metallic precursor compounds on an interior
surface of sealed NMR tubes;
[0118] FIG. 31A is an ORTEP drawing of the X-ray crystal structure
of N,N,N',N'-tetraisopropylformamidinylidene copper
hexamethyldisilazide (19a);
[0119] FIG. 31B is an ORTEP drawing of the X-ray crystal structure
of N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide (17a);
[0120] FIG. 32 is a graph of vapour pressure plots for two acyclic
diaminocarbene-containing mono-metallic precursor compounds in
comparison to a control (copper
bis-(2,2,6,6-tetramethyl-3,5-heptadionate);
[0121] FIG. 33 is a weight loss curve for
N,N,N',N'-tetramethylformamidinylidene copper hexamethyldisilazide
(17a);
[0122] FIG. 34 is a weight loss curve for
N,N,N',N'-tetraisopropylformamidinylidene copper
hexamethyldisilazide (19a);
[0123] FIG. 35 is a graph of vapour pressure plots for
1,3-diisopropyl-imidazolin-2-ylidene silver hexamethyldisilazide
(2b) and 1,3-disopropyl-imidazolin-2-ylidene gold
hexamethyldisilazide (2c) precursor compounds in comparison to a
control (copper bis-(2,2,6,6-tetramethyl-3,5-heptadionate);
[0124] FIG. 36 depicts weight loss curves for
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) with heating;
[0125] FIG. 37 is a .sup.1H NMR spectrum of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) prior to heating; and
[0126] FIG. 38 is a .sup.1H NMR spectrum of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) after heating at 92.degree. C. for 15
days.
DETAILED DESCRIPTION
[0127] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs.
[0128] Unless the context clearly indicates otherwise, as used
herein plural forms of the terms herein are to be construed as
including the singular form and vice versa.
[0129] The terms "comprises" and "comprising" as used herein will
be understood to mean that the list following is non-exhaustive and
may or may not include any other additional suitable items, for
example one or more further feature(s), component(s) and/or
ingredient(s) as appropriate.
[0130] As used herein, "aliphatic" refers to hydrocarbon moieties
that are linear, branched or cyclic, may be alkyl, alkenyl or
alkynyl, may be substituted or unsubstituted and may include one or
more heteroatoms. "Alkenyl" means a hydrocarbon moiety that is
linear, branched or cyclic and comprises at least one carbon to
carbon double bond. "Alkynyl" means a hydrocarbon moiety that is
linear, branched or cyclic and comprises at least one carbon to
carbon triple bond. "Aryl" means a moiety including a substituted
or unsubstituted aromatic ring, including heteroaryl moieties and
moieties with more than one conjugated aromatic ring; optionally it
may also include one or more non-aromatic ring. "C.sub.5 to C.sub.8
Aryl" means a moiety including a substituted or unsubstituted
aromatic ring having from 5 to 8 carbon atoms in one or more
conjugated aromatic rings. Examples of aryl moieties include
phenyl.
[0131] As used herein, the term "aliphatic" includes "short chain
aliphatic" or "lower aliphatic," which refers to C.sub.1 to C.sub.4
aliphatic, and "long chain aliphatic" or "higher aliphatic," which
refers to C.sub.5 to C.sub.12 aliphatic.
[0132] "Heteroaryl" means a moiety including a substituted or
unsubstituted aromatic ring having from 4 to 8 carbon atoms and at
least one heteroatom in one or more conjugated aromatic rings. As
used herein, "heteroatom" refers to non-carbon and non-hydrogen
atoms, such as, for example, O, S, and N. Examples of heteroaryl
moieties include pyridyl, furanyl and thienyl.
[0133] "Alkylene" means a divalent alkyl radical, e.g.,
--C.sub.fH.sub.2f-- wherein f is an integer. "Alkenylene" means a
divalent alkenyl radical, e.g., --CHCH--.
[0134] "Substituted" means having one or more substituent moieties
whose presence does not interfere with the desired function or
reactivity. Examples of substituents include alkyl, alkenyl,
alkynyl, cycloalkyl (non-aromatic ring), Si(alkyl).sub.3,
Si(alkoxy).sub.3, alkoxyl, amino, alkylamino, alkenylamino, amide,
amidine, guanidine, hydroxyl, thioether, alkylcarbonyl,
alkylcarbonyloxy, alkoxycarbonyloxy, carbonate, alkoxycarbonyl,
aminocarbonyl, alkylthiocarbonyl, phosphate, phosphate ester,
phosphonato, phosphinato, cyano, halo, acylamino, imino,
sulfhydryl, alkylthio, thiocarboxylate, dithiocarboxylate, sulfate,
sulfato, sulfonate, sulfamoyl, sulfonamide, nitro, nitrile, azido,
heterocyclyl, ether, ester, silicon-containing moieties, thioester,
or a combination thereof. The substituents may themselves be
substituted. For instance, an amino substituent may itself be mono
or independently disubstituted by further substituents defined
above, such as alkyl, alkenyl, alkynyl, and cycloalkyl
(non-aromatic ring).
[0135] As used herein, the term "unsubstituted" refers to any open
valence of an atom being occupied by hydrogen. Also, if an occupant
of an open valence position on an atom is not specified then it is
hydrogen.
[0136] As used herein, the terms "deposition process" and "vapour
deposition process" refer to a process in which a metal layer is
formed on one or more surfaces of a substrate from vaporized
precursor composition(s) including one or more metal-containing
compounds. The metal-containing compounds are vaporized and
directed to and/or contacted with one or more surfaces of a
substrate (e.g., semiconductor substrate or substrate assembly)
placed in a deposition chamber. Typically, the substrate is heated.
These metal-containing compounds form a non-volatile, thin,
uniform, metal-containing layer on the surface(s) of the substrate.
As used herein, a "vapour deposition process" can be a chemical
vapour deposition processes (including pulsed chemical vapour
deposition processes) or an atomic layer deposition process.
[0137] As used herein, the term "chemical vapour deposition" or
"CVD" refers to a vapour deposition process wherein the desired
layer is deposited on the substrate from vaporized metal-containing
compounds (and any reaction gases used) within a deposition chamber
with no effort made to separate the reaction components.
[0138] As used herein, the term "atomic layer deposition" or "ALD"
as used herein refers to a vapour deposition process in which
deposition cycles, preferably a plurality of consecutive deposition
cycles, are conducted in a process chamber (i.e., a deposition
chamber). Typically, during each cycle the precursor is chemisorbed
to a deposition surface (e.g., a substrate assembly surface or a
previously deposited underlying surface such as material from a
previous ALD cycle), forming a monolayer or sub-monolayer that does
not readily react with additional precursor (i.e., a self-limiting
reaction). Thereafter, if necessary, a reactant (e.g., another
precursor or reaction gas) may be introduced into the process
chamber for use in converting the chemisorbed precursor to the
desired material on the deposition surface. Typically, this
reactant is capable of reaction with the already chemisorbed
precursor. Further, purging steps may also be utilized during each
cycle to remove excess precursor from the process chamber and/or
remove excess reactant and/or reaction by-products from the process
chamber after conversion of the chemisorbed precursor.
[0139] As compared to the one step CVD process, the longer duration
multi-cycle ALD process provides improved control of layer
thickness and composition by self-limiting layer growth, and
minimizes detrimental gas phase reactions by separation of the
reaction components. The self-limiting nature of ALD provides a
method of depositing a film on a wide variety of reactive surfaces,
including surfaces with irregular topographies, with better step
coverage than is available with CVD or with other "line of sight"
deposition methods such as evaporation or physical vapour
deposition (PVD or sputtering).
[0140] As used herein, the term "bubbler" is used to refer to a
component of a metal deposition system that is a container in which
a solid or liquid precursor is converted to its vapour form using
heat and an inert gas bubbled into the container and through the
precursor. The bubbler typically includes an inlet tube at the
bottom of the container through which the inert gas is introduced
into the chamber. The mixture of the inert gas and the precursor
vapour exit the bubbler into the deposition chamber.
[0141] As used herein, the term "carbene" is a molecule comprising
a neutral carbon atom with a valence of two, and two valence
electrons available for formation of a dative bond (i.e., with a
metal fragment or complex). An "N-heterocyclic carbene" or "NHC" is
a type of diaminocarbene in which the carbenic carbon is part of a
nitrogen-containing heterocycle, such as an imidazole.
[0142] As used herein, the term "dative bond" refers to a
coordinate covalent bond in which the shared electrons come from
one of the atoms only.
[0143] As used herein, the terms "saturated N-heterocyclic
carbene", "saturated N-heterocyclic diaminocarbene", "saturated
NHC", and "sNHC" refer to diamino heterocyclic carbenes in which
the carbenic carbon connects the two nitrogen atoms. The remaining
carbon atoms in the heterocycle are saturated (i.e., they are
connected via single bonds). Typically, the sNHC is a five membered
or a six membered heterocycle.
[0144] As used herein, the term "acyclic carbene" or "acyclic
diaminocarbene" refers to non-cyclic diamino carbenes in which the
carbenic carbon connects the two nitrogen atoms.
[0145] As used herein, the term "group 11 metal" refers to the
transition metals in group 11 of the periodic table, which are
copper (Cu), silver (Ag) and gold (Au). Although roentgenium (Rg)
belongs to this group of elements based on its electronic
configuration, it is a short-lived transactinide and, therefore,
not included within the term "group 11 metals" as used herein.
[0146] The term "anionic ligand" as used herein, refers to an
anionic ligand bound to a metal centre. As described herein, the
anionic ligand in the precursor compounds does not comprise a
halogen atom directly bound to the metal centre. Preferably, the
anionic ligand is a nitrogen-containing, two coordinate, negatively
charged ligand. The anionic ligand can be, for example, amide
(--NR.sub.2), heterocycle (such as, e.g., piperidine, pyrrolidine),
cyclopentadiene, alkoxide, alkyl, hydride, hydroxide, diketonate,
diketiminate, amidinate, or guanidinate. Preferably, the anionic
ligand does not comprise a halogen atom at any position.
[0147] The term "amide" as used herein, refers to the anion
NR.sub.2.sup.- or --NR.sub.2, where each R is independently an
optionally substituted linear, branched or cyclic aliphatic group,
an optionally substituted linear or straight alkylsilyl, or the two
R groups together with the amide nitrogen form an optionally
substituted heterocycle.
[0148] As used herein, and as would be understood by a worker
skilled in the art, the term "sccm" is an acronym for Standard
Cubic Centimetres per Minute, which is a unit of fluid flow (e.g.,
gas flow) at standard temperature and pressure.
[0149] As used herein, the abbreviation "Cu(tmhd).sub.2" refers to
copper bis-(2,2,6,6-tetramethyl-3,5-heptadionate).
[0150] Precursor Compounds
[0151] Atomic layer deposition (ALD) is intrinsically different
from chemical vapour deposition (CVD), which means that precursor
compounds include particular characteristics in order to be useful
in ALD. In CVD, the precursor compounds react together at the
substrate surface to produce the target film, or a precursor
compound reacts with itself at the substrate surface to produce the
target film (i.e., single source CVD). In contrast, precursor
compounds useful in ALD react with the substrate surface to produce
a chemically active, adsorbed monolayer. It is then this monolayer
that subsequently reacts with a second precursor compound to form
the target film (see FIG. 1). Thus, the design and function of a
precursor compound for ALD is fundamentally different from the
design and function of a precursor compound useful in CVD.
[0152] ALD precursor compounds are generally designed around the
following five principles: [0153] 1. The precursor compound must
form a self-limiting monolayer with the substrate: the precursor
compound needs to react at the growing surface sufficiently to
adsorb and form a single monolayer of a surface species; the
precursor compound cannot react entirely to form the target film,
or else step-wise growth is not possible. [0154] 2. The precursor
compound must be sufficiently volatile to vaporize effectively and
permit uniform vapour delivery during ALD: factors that can
contribute to sufficient volatility include, but are not limited
to, molecular weight (low molecular weight can increase
volatility), asymmetry, steric bulk (low steric bulk can increase
volatility), and intermolecular interactions (low intermolecular
interactions can increase volatility). [0155] 3. The precursor
compound should be liquid at the process temperature since
precursors need to volatilise at a steady rate. The surface area of
solid material varies as volatilisation occurs, which causes
changes in particle size and accumulation of impurities at the
surface. Consequently, the kinetics of volatilisation change during
volatilisation. However, liquids have a continuously refreshed and
unchanging surface area, which allows a steady kinetics of
evaporation. [0156] 4. The precursor compound must be sufficiently
thermally stable to permit controlled, stepwise growth of the film
and to resist decomposition while being heated over extended
periods of time: if the precursor compounds decompose, for example,
in the source container or during the deposition process, this can
greatly increase impurity level or cause non-self-limiting growth.
[0157] 5. The precursor compound must be chemically reactive: the
precursor needs to be sufficiently reactive to chemisorb to form a
monolayer on a substrate and to react with the subsequent precursor
to form a target film.
[0158] CVD precursors are generally designed following principles
2-4 above. However CVD precursors are designed to continuously
react to form the target film; they do not stop reacting following
formation of a monolayer. This difference in chemical reactivity is
the most important factor that differentiates an ALD precursor from
a CVD precursor.
[0159] A precursor compound useful in an ALD process will ideally
include some or all of the following characteristics: it will be a
solid or liquid at room temperature to facilitate handling; it will
be a liquid at process temperature with sufficient volatility to
vaporize effectively to permit uniform vapour delivery; it will be
thermally stable to permit controlled, stepwise growth of the film
and to resist decomposition in inlet devices while being heated
over extended periods of time; it will form a monolayer at a range
of temperatures to allow processes to be developed over a wide
range of reaction conditions; and it will react effectively with
its subsequent precursor.
[0160] The mono-metallic precursor compounds described herein are
highly volatile and highly thermally stable. In order for a
precursor compound to be considered "highly volatile", it will
achieve a vapour pressure of at least about 1 torr at 160.degree.
C. In order for a precursor compound to be considered "highly
thermally stable", it remains stable at the required process
temperature for extended periods (preferably 1 or more days, 2 or
more days, 1 or more weeks, or 2 or more weeks) and will remain
stable for those periods of time at temperatures up to at least
about 100.degree. C., 150.degree. C., 200.degree. C., 300.degree.
C., 350.degree. C. or 400.degree. C. As would be readily
appreciated by a worker skilled in the art, the stability of the
precursor compound can change depending on its physical state. For
example, when the precursor is in a liquid state (as it usually is
in the bubbler used for ALD), then the precursor compound will
remain stable for extended periods of time at temperatures up to at
least about 100.degree. C., 150.degree. C. or 200.degree. C.
[0161] In accordance with one embodiment, the precursor compound
will exhibit less than about 2% decomposition (by weight), or less
than about 1% decomposition (by weight) following 1 week at about
10.degree. C. above ALD source temperature.
[0162] The mono-metallic precursor compounds described herein have
been developed to be useful in ALD, however, it should be readily
apparent that these compounds may also be useful in other metal
deposition processes, such as CVD.
[0163] In accordance with one aspect, there is provided a
mono-metallic precursor compound comprising a diaminocarbene (DAC)
having the general formula of Formula I:
DAC-M-X I
where M is a metal; and X is an anionic ligand, and where the DAC
is a diaminocarbene that is an optionally substituted, saturated
N-heterocyclic diaminocarbene (sNHC) or an optionally substituted
acyclic diaminocarbene. In a preferred embodiment, M is a group 11
metal, such as copper, silver or gold.
[0164] In accordance with one aspect, there is provided a
mono-metallic precursor compound comprising an sNHC having the
general formula of Formula I:
sNHC-M-X Ia
where M is metal; and X is an anionic ligand. In a preferred
embodiment, M is a group 11 metal, such as copper, silver or
gold.
[0165] As defined above, the DAC component of the precursor
compound is a diaminocarbene having a carbenic atom bridging two
nitrogen atoms. The metal is bound to the DAC at the carbenic atom
via a dative bond. Also, M is bound to X at a non-halogenic atom of
the anionic ligand, in order to avoid contamination by halogen
during metal deposition. In a specific embodiment, the anionic
ligand does not include a halogen atom at any position.
[0166] The precursor compound defined above does not comprise any
aryl or heteroaryl group.
[0167] In one embodiment of the group 11 mono-metallic precursor
compound is a compound of Formula IIa:
##STR00005##
[0168] X is an anionic ligand; [0169] M is a metal, for example a
group 11 metal, such as, copper, silver or gold; [0170] Y is
CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or NR.sup.9; [0171]
R.sup.1 and R.sup.2 are each independently H, or an optionally
substituted, branched, straight or cyclic aliphatic group, wherein
R.sup.1 and R.sup.2 do not comprise a halo substituent; [0172]
R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently H, or
an optionally substituted, branched, straight or cyclic aliphatic
group; and [0173] R.sup.9 is absent or H, or an optionally
substituted, branched, straight or cyclic aliphatic group, wherein,
when R.sup.9 is absent, the bond between N and the adjacent C is a
double bond and R.sup.3 or R.sup.4 is absent,
[0174] and wherein the compound does not comprise an aryl or
heteroaryl group, and M is bound to a non-halogenic atom of X. In a
preferred embodiment, M is a group 11 metal, such as copper, silver
or gold.
[0175] In accordance with another aspect, there is provided a
compound of Formula IIb:
##STR00006##
[0176] wherein [0177] X is an anionic ligand; [0178] M is a metal,
for example, a group 11 metal, such as, copper, silver or gold; and
[0179] each R.sup.1 and R.sup.2 is independently H, or an
optionally substituted, branched, straight or cyclic aliphatic
group, wherein R.sup.1 and R.sup.2 do not comprise a halo
substituent, [0180] and wherein the compound does not comprise an
aryl or heteroaryl group and M is bound to a non-halogenic atom of
X.
[0181] It should be understood that in the compound of Formula IIb,
the two R.sup.1 substituents can be different from one another and
from each of the two R.sup.2 substituents. Similarly, it should be
understood that the two R.sup.2 substituents can be different from
one another and from each of the two R.sup.1 substituents.
Specifically, the structure of Formula IIb encompasses compounds
having four different substituents at the two nitrogens.
[0182] In accordance with a specific embodiment, M is Cu(I), Ag(I)
or Au(I). In accordance with a more specific embodiment, M is
Cu(I).
[0183] In accordance with a specific embodiment, X is:
##STR00007##
where R.sup.7 and R.sup.8 are each independently an optionally
substituted linear, branched or cyclic aliphatic group, an
optionally substituted linear or straight C.sub.1 to C.sub.12
alkylsilyl, or R.sup.7 and R.sup.8 together with the amide nitrogen
form an optionally substituted heterocycle.
[0184] In accordance with certain embodiments, R.sup.1, R.sup.2,
R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently H, an
optionally substituted C.sub.1 to C.sub.12 alkyl or heteroalkyl or
an optionally substituted C.sub.3 to C.sub.12 cycloalkyl or cyclic
heteroalkyl. In alternative embodiments, R.sup.1, R.sup.2, R.sup.3,
R.sup.4, R.sup.5 and R.sup.6 are each independently H, an
optionally substituted C.sub.1 to C.sub.6 alkyl or heteroalkyl or
an optionally substituted C.sub.3 to C.sub.8 cycloalkyl or cyclic
heteroalkyl.
[0185] In accordance with a particular embodiment, R.sup.1 and
R.sup.2 are each independently H, an optionally substituted
branched or straight C.sub.1 to C.sub.12 alkyl or heteroalkyl,
wherein R.sup.1 and R.sup.2 do not comprise any halide atoms.
[0186] In accordance with another particular embodiment the anionic
ligand X is selected such that there are no metal-oxygen bonds
(e.g., Cu--O) within the mono-metallic precursor compound. In a
related embodiment, the mono-metallic precursor compound does not
form metal oxide films when used in ALD. Alternatively, if the
absence of oxygen is not required, the anionic ligand X can be an
oxygen containing ligand, such as an alkoxide, bound to the metal
via the oxygen atom.
[0187] In accordance with another embodiment, the precursor
compound does not include any oxygen atoms. For example, the
presence of oxygen anywhere in the precursor can lead to oxidation
of oxidizable layers, such as the tantalum nitride barrier layer
often used in semiconductor manufacture. Similarly, the reactive
gas should not contain oxygen when the metal deposition substrate
includes an oxidizable layer, such as a tantalum nitride barrier
layer.
[0188] Another consideration in selection of an anionic ligand is
the presence of hydrogen atoms in the ligand at a position beta to
the metal atom. The presence of .beta.-hydrogen atoms can result in
decomposition of the precursor compound via elimination of the
ligand with concomitant formation of unstable metal hydrides.
[0189] Metal hydrides are commonly unstable and very reactive.
.beta.-Hydrogen eliminations occurring in a precursor source
container would deplete the precursor as well as create unwanted
reactive species. .beta.-Hydrogen elimination at the deposition
surface would lead to non self-limiting behaviour, i.e., CVD
growth. This can be avoided by not having .beta.-hydrogens in the
anionic ligand or by designing the anionic ligand so that any
.beta.-hydrogens are not accessible to the metal center (i.e.,
there is no reaction pathway for the .beta.-hydrogen to form a
intermediate bond that would lead to .beta.-hydride transfer).
[0190] As described above, decreasing steric bulk can increase
volatility of a precursor compound because of a concomitant
decrease in molecular weight. Accordingly, steric bulk is one
consideration for selection of the anionic ligand and the
substituents on the sNHC. Although decreasing steric bulk can
increase volatility of the precursor compound, care must be taken
to maintain sufficient steric bulk to avoid formation of dimeric
complexes.
[0191] Specific examples of group 11 mono-metallic precursor
compounds are shown below:
##STR00008## ##STR00009## ##STR00010##
[0192] Compounds 1a, b, c to 21a, b, c, are useful as precursor
compounds in ALD. In some instances, compounds 1a, b, c to 21a, b,
c may also be useful in CVD.
[0193] U.S. Patent Publication No. 2009/0004385, which is herein
incorporated by reference in its entirety, discloses a limited
number of compounds having the general structure:
NHC--Cu--Y
where the NHC is an imidazol-2-ylidene, the Cu is bound to the NHC
at the carbenic atom and Y is an anionic ligand. The disclosed
compounds all include an unsaturated NHC. These compounds are
purported to be useful as copper precursors in chemical phase
deposition, such as ALD.
[0194] Interestingly, however, the present inventors have found
that a compound having the structure of Formula III
(1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper
hexamethyldisilazide), shown below, which comprises an unsaturated
NHC, was unsuccessful as a copper precursor in ALD.
##STR00011##
[0195] As detailed in the Examples below, the compound 2a was used
to successfully deposit a copper thin film on a substrate in an ALD
process. Compound 2a was volatilised at 90.degree. C. and deposited
copper by plasma-enhanced ALD at 225.degree. C. using H.sub.2 (20
sccm) in Ar (140 sccm) as the plasma supply gas. The growth rate
for the films was about 0.21 .ANG./cycle. A saturation curve was
generated (FIG. 22), which confirmed that this process undergoes
self-limited (i.e., ALD) growth.
[0196] Copper metal deposition was attempted using the compound of
Formula III, which is an unsaturated analogue of compound 2a, under
conditions similar to those successfully employed with compound 2a.
With the compound of Formula III used as the precursor, copper
metal could not be repeatably deposited. During the process, spots
of copper as well as spots of non-conductive, apparently
transparent material were commonly co-deposited. This led to the
conclusion that this precursor did not produce a stable,
self-limiting monolayer. Rather it may have undergone thermal
decomposition to produce a film that incorporated copper as well as
a large amount of impurities from the ligand system.
[0197] Without wishing to be bound by theory, the suitability of
the precursor compounds of Formulae Ia and Ha for ALD may be due to
the saturated and sterically accessible backbone of the sNHC.
Alternatively, or in addition, the poor results obtained using the
compound of Formula III in ALD may result from intermolecular
stacking of molecules of the compound of Formula III resulting in
reduced accessibility and/or reactivity. As shown in FIG. 3, the
unsaturated N-heterocyclic carbene in the compound of Formula III
is planar, which likely results in intermolecular stacking
(sometimes referred to as .pi.-stacking although the interactions
between the N-heterocyclic carbene may not be limited to .pi.-.pi.
interactions), thus reducing the reactivity of the compound and its
suitability for ALD. The sNHC-containing mono-metallic precursor
compounds described herein are designed such that they do not
comprise any aryl or heteroaryl functional groups in order to avoid
such intermolecular stacking.
[0198] International PCT Publication No. WO 2006/012294, which is
herein incorporated by reference in its entirety, discloses a broad
class of main group and transition metal chemical vapour deposition
precursors that incorporate nucleophilic stable carbene ligands.
Within the broad class of carbene ligands, WO 2006/012294
generically identified sNHCs without identifying any specific sNHC
ligands as being made or tested in precursor compounds. The
purported precursors disclosed in WO 2006/012294 were suggested to
be useful in CVD only. Nowhere in WO 2006/012294 is there any
teaching or discussion relating to ALD.
[0199] The mono-metallic precursor compounds of Formula I, Ia, IIa
and IIb, as described herein, have now been found to be effective
precursors in ALD of a metal to a substrate, for example,
deposition of a thin film of copper to a substrate.
[0200] As described above, there are five principles used in
designing ALD precursors. The identification of precursors having
sufficient volatility and thermal stability can be achieved by
various means. A specific example of a useful technique is
thermogravimetric ("TG") analysis.
[0201] TG analysis measures the amount and rate of change in the
mass of a sample as a function of temperature (".DELTA.m/.DELTA.T")
or time (".DELTA.m/.DELTA.t") in a controlled atmosphere. As used
in the present application, the measurements are used primarily to
determine the thermal stabilities of precursor compounds, as well
as their volatility.
[0202] TG analysis measurements provide valuable information that
can be used to select precursor compounds useful in ALD and to
predict precursor performance. In a typical TG analysis, a
precursor compound under study is subjected to increasing
temperatures with mass measurements obtained at set time
intervals.
[0203] A TG graph can be used to demonstrate the volatility of a
potential precursor compound. In a TG graph, a volatile compound
will produce a curve demonstrating a slow onset of weight loss
followed by a rapid drop off. A low residual mass (e.g., <2%)
following a TG experiment, is a definite indicator of compound
volatility. A residual mass that is >2%, but less than the metal
content of the complex is indicative of, at least, partial
volatility of a metal-containing species during the experiment.
[0204] A TG graph can also be used to demonstrate the thermal
stability of a potential precursor compound. A single featured
weight loss curve that is characteristic of volatility and has a
residual mass of <2% is an indicator that the compound was
thermally stable within the temperature range and time span of the
weight loss event.
[0205] TG analyses performed using sNHC-containing mono-metallic
precursor compounds as described herein and an unsaturated analog
thereof, have shown that the sNHC-containing compounds have
superior volatility and thermal stability in comparison to an
unsaturated analog. Details of these analyses are provided in the
Examples below.
[0206] Synthesis
[0207] The DAC precursor compounds can be prepared using a variety
of synthetic methods. The synthetic reactions shown in the below
scheme and described herein, are illustrative only. Other synthetic
routes can be employed, as would be within the abilities of a
worker skilled in the art, based on the disclosure herein.
[0208] In accordance with one embodiment, the metal precursor
compounds can be prepared using a method that employs salt
metathesis. A specific example of such a synthetic method is
depicted in the scheme below:
##STR00012##
where X is a anionic ligand;
[0209] M is a group 11 metal, for example, copper, silver or
gold;
[0210] B is a halide, such as a chloride, bromide or iodide;
[0211] Y is CR.sup.5R.sup.6, (CR.sup.5R.sup.6).sub.2, or
NR.sup.5;
[0212] R.sup.1 and R.sup.2 are each independently H, or an
optionally substituted linear, branched or cyclic aliphatic group,
wherein R.sup.1 and R.sup.2 do not comprise any halide atoms;
and
[0213] R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently
H, or an optionally substituted linear, branched or cyclic
aliphatic group.
[0214] In one embodiment, R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5 and R.sup.6 are each independently H, a C.sub.1 to C.sub.12
alkyl or heteroalkyl, or a C.sub.3 to C.sub.12 cycloalkyl or cyclic
heteroalkyl.
[0215] As would be appreciated by a worker skilled in the art,
although the above method includes the use of a lithium salt, the
method can also be performed using a different salt of the anionic
ligand, such as a sodium or potassium salt.
[0216] The carbene metal halide compound can be provided as an
isolated starting material or an unisolated intermediate. In either
option the carbene metal halide can be synthesized by treating a
carbene salt, such as a carbene halide salt, with a group 11 metal
halide, such as CuCl, under basic conditions.
[0217] In accordance with another embodiment, the compounds can be
synthesized by a method including the step of cleaving a metal
oligomer, or metal dimer, with a saturated NHC.
[0218] Alternatively, the mono-metallic precursor compounds can be
prepared using a synthetic route analogous to the method used in
U.S. Patent Publication No. 2009/0004385 to prepare copper
precursors that contain an unsaturated NHC.
[0219] In another alternative, the mono-metallic precursor
compounds can be prepared using a methane elimination and ligand
exchange as described in Inorg. Chem, 2006, 45(22), 9032-9045.
[0220] In an alternative approach, the starting materials are
sNHC.HCl, CuCl, and two equivalents of base to make the final
complex. In this approach, the base would be the amide salt.
[0221] Following synthesis, the precursor compounds can be purified
if the product of the synthetic method is not sufficiently pure to
be used in ALD. For example, the precursor compounds can be
purified by recrystallization, distillation, sublimation in a
sublimation apparatus, or any combination thereof. Examples of
suitable sublimation apparatuses are depicted in FIGS. 4-6. In
accordance with one embodiment, the precursor compounds are
sufficiently pure to be used in ALD, for example, to produce a film
of at least about 95% purity. In accordance with a specific
embodiment, the precursor compounds are at least 95% pure.
Preferably, the precursor compounds are at least 98% pure. More
preferably, the precursor compounds are 99.98% pure (e.g., when
prepared as electronic grade chemicals).
[0222] Metal Deposition
[0223] The DAC metal precursor compounds disclosed herein are
useful in deposition of metal thin films by any deposition methods
known to those of skill in the art. Examples of suitable deposition
techniques include, without limitation chemical vapour deposition
(CVD), plasma enhanced chemical vapour deposition (PE-CVD), atomic
layer deposition (ALD), plasma enhanced atomic layer deposition
(PE-ALD) and the like. Accordingly, another aspect provides a
method and system for deposition of a thin film of metal on a
substrate using a DAC metal precursor compound.
[0224] In an embodiment, a first precursor is introduced into a
reactor in vapour form. The precursor in vapour form can be
produced by vaporizing a liquid precursor solution, through a
conventional vaporization step such as direct vaporization,
distillation, or by bubbling an inert gas (e.g. N.sub.2, He, Ar,
etc.) into the precursor solution and providing the inert gas plus
precursor mixture as a precursor vapour solution to the reactor.
Bubbling with an inert gas can also remove any dissolved oxygen
present in the precursor solution. In other alternatives, the
precursor is introduced into the reactor via liquid injection or an
aerosol-assisted bubbler.
[0225] The reactor can be any enclosure or chamber within a device
in which deposition methods take place such as without limitation,
a cold-wall type reactor, a hot-wall type reactor, a single-wafer
reactor, a multi-wafer reactor, or other types of deposition
systems, under conditions suitable to cause the precursors to react
and form the layers. Specific, non-limiting, example of reactors
suitable for ALD using an DAC metal precursor are the F-120 ALD
reactor (ASM Microchemistry Ltd., Finland; for thermal ALD) and the
TFS 200 ALD reactor (BENEQ, Finland; for plasma ALD) and the
SUNALE.TM. R-200 ALD reactor (Picosun, Finland; for plasma
ALD).
[0226] Generally, the reactor contains one or more substrates onto
which the thin films will be deposited. The one or more substrates
can be any suitable substrate used, for example, in semiconductor,
photovoltaic, flat panel, or LCD-TFT device manufacturing, or
non-electronic applications such as optics, catalysis, sensors and
so on. Alternatively, a thin film/substrate composite material is
useful in microelectromechanical systems (MEMS), such as sensors,
thermal actuators, voltaic actuators, accelerometers, microfluidic
devices, etc.
[0227] Examples of suitable substrates include without limitation,
glass, TaN, TiN, sapphire, indium tin oxide (ITO), SiO.sub.2,
silicon, silicon nitride, silicon oxy nitride, silicon oxycarbide,
fused silica, polymeric materials, tungsten, tantalum, ruthenium,
other metals, organic materials or combinations thereof. The
substrate can also have one or more layers of differing materials
already deposited upon it from a previous manufacturing step.
Optionally, the surface of the substrate is cleaned, using standard
methods, prior to the film deposition process.
[0228] In some embodiments, in addition to the first precursor, a
reactant gas or a secondary precursor, can be introduced into the
reactor at the appropriate time. In some of these embodiments, the
reactant gas can be an oxidizing gas such as one of oxygen, ozone,
water, hydrogen peroxide, nitric oxide, nitrogen dioxide, radical
species of these, as well as mixtures of any two or more of these.
In some other of these embodiments, the reactant gas can be a
reducing agent such as one of hydrogen, a forming gas (i.e.,
.about.5% hydrogen, .about.95% nitrogen mixture) ammonia, a silane,
a borane, an amino borane, an alane, formic acid, a hydrazine
(e.g., dimethylhydrazine), a radical species of thereof, or a
mixture of any two or more of these reducing agents.
[0229] In an alternative embodiment, the reactant gas can be a
formic acid/hydrazine combination (Knisley, T. J., et al., Chem.
Mater., 2011, 23, 4417-4419) or ethyl iodide (Au, Y., Lin, Y., and
Gordon, R. G., J. Elect. Soc., 2011, 158(5), D248-D253). When ethyl
iodide is employed as the reactant gas, the method is useful for
bottom-up filling. Bottom-up filling of features with high aspect
ratios is an improvement for CVD to fill features without seams or
voids. It has been shown that pre-treatment of suitable substrates
with ethyl iodide vapour leads to accelerated film growth for
copper CVD processes using copper(I) diketonates and copper(I)
amidinates. Without wishing to be bound by theory, it is thought
that dissociated iodine atoms on the surface weaken the copper
ligand bond and ease the reduction to copper metal by a reducing
agent. When an ethyl iodide pre-treatment step is used to fill
features of high aspect ratios, growth at the bottom of the feature
continuously accelerates as the surface area decreases and the
iodine atom concentration increases there by allowing for bottom-up
filling and eliminating seems and voids in the feature.
[0230] In some embodiments, and depending on what type of film is
desired to be deposited, a second metal-containing precursor can be
introduced into the reactor. Such a second metal-containing
precursor can comprise a metal source, such as, but not limited to,
copper, silver, gold, praseodymium, manganese, ruthenium, titanium,
tantalum, bismuth, zirconium, hafnium, lead, niobium, magnesium,
aluminum, tungsten, lanthanum, or mixtures of these, which is the
same or different as the metal in the first precursor. In
embodiments where a second metal-containing precursor is utilized,
the resultant film deposited on the substrate can contain at least
two different metal types in separate layers of a multilayer film,
where the first metal-containing precursor, the second
metal-containing precursor, or both, is a DAC metal containing
precursor as described herein. Alternatively, in embodiments where
a second metal-containing precursor is used, the film deposited on
the substrate comprises at least two different metals within one or
more layers of a multilayer film.
[0231] The first precursor and any optional reactants or precursors
can be introduced sequentially (as in ALD) or simultaneously (as in
CVD) into the reaction chamber. In some embodiments, the reaction
chamber is purged with an inert gas between the introduction of the
precursor and the introduction of the reactant. In some
embodiments, the reactant can be excited species contained in a
plasma. One of skill in the art would generally recognize methods
and apparatus suitable for plasma reaction with an ALD or CVD
precursor.
[0232] Depending on the particular process parameters, deposition
can take place for a varying length of time. Generally, deposition
can be allowed to continue as long as desired or necessary to
produce a film with the necessary properties. Typical film
thicknesses may vary from several angstroms to several hundreds of
microns, depending on the specific deposition process. The
deposition process can be performed as many times as necessary to
obtain the desired film properties or thickness.
[0233] In some embodiments, the temperature and the pressure within
the reactor are held at conditions suitable for ALD or CVD
depositions. For instance, the pressure in the reactor may be held
between about 1 Pa and about 10.sup.5 Pa, or preferably between
about 25 Pa and 10.sup.3 Pa, as required per the deposition
parameters. Likewise, the temperature in the reactor may be held
between about 50.degree. C. and about 500.degree. C., preferably
between about 50.degree. C. and about 400.degree. C.
[0234] In some embodiments, the precursor vapour solution and the
reaction gas, can be pulsed sequentially or simultaneously (e.g.,
pulsed CVD) into the reactor. Each pulse of precursor can last for
a time period ranging from about 0.01 seconds to about 10 seconds,
alternatively from about 0.3 seconds to about 8 seconds,
alternatively from about 1 seconds to about 6 seconds. In another
embodiment, the reaction gas may also be pulsed into the reactor.
In such embodiments, the pulse of each gas may last for a time
period ranging from about 0.01 seconds to about 10 seconds,
alternatively from about 0.3 seconds to about 8 seconds,
alternatively from about 1 seconds to about 6 seconds.
[0235] As described above, ALD is an alternative method to CVD for
depositing conformal, ultra-thin films at comparatively lower
temperatures. ALD is similar to CVD except that the substrate is
sequentially exposed to one reactant at a time, or one dose of a
reactant at a time. This means that the films are expected to be
more uniform and more readily controlled when manufactured using
ALD rather than CVD.
[0236] ALD is described in Finnish patent publications 52,359 and
57,975 and in U.S. Pat. Nos. 4,058,430 and 4,389,973. Apparatuses
suited to implement these methods are disclosed in U.S. Pat. Nos.
5,855,680, 6,511,539, and 6,820,570, Finnish Patent No. 100,409
Material Science Report 4(7)(1989), p. 261, and Tyhijiotekniikka
(Finnish publication for vacuum techniques), ISBN 951-794-422-5,
pp. 253-261, which are incorporated herein by reference in their
entirety. A basic ALD apparatus includes a reactant chamber, a
substrate holder, a gas flow system including gas inlets for
providing reactants to a substrate surface and an exhaust system
for removing used gases. Apparatuses for ALD are commercially
available.
[0237] Thermal ALD of metals relies on thermally-activated
reactions between two precursors: a metal-containing precursor
compound and a reactant precursor, such as a reducing agent. This
method may be preferred in situations in which a clean process is
required and/or where specialized equipment is not available. FIG.
1 provides a general schematic of a thermal deposition process
using a copper precursor compound and a reducing agent.
[0238] In one example of thermal ALD using, for example, an ASM
F-120 reactor, a small amount of precursor (0.3-0.5 g) is loaded
into an open-topped precursor boat. This boat is inserted into the
source tube of the reactor. Another source tube is fitted with
hydrogen gas using a vacuum flange, and the flow is controlled to
about 10 sccm with a mass flow controller. In a specific example, a
5 cm.times.5 cm silicon substrate (with its native oxide intact) is
submitted to the deposition zone, and the entire apparatus is
brought down to roughing pump vacuum. The precursor boat is heated
to 90.degree. C., and the substrate is heated to 225.degree. C.
Generally, there is a uniform ramp of temperature between the
precursor boat and the deposition zone to prevent condensation of
the precursor in the apparatus. Nitrogen gas, or another inert gas,
is used in a continual purge of about 100 sccm to purge the
reactor, and through controlling the valving, this purge gas is
also used as a carrier gas for the precursor and a reducing gas,
such as hydrogen. The valving can be programmed to deliver a pulse
of precursor for 2 seconds, with a purge of 2 seconds. This can be
followed by a pulse of hydrogen for 2 seconds, followed by a purge
of 2 seconds. In a typical experiment, this pulse sequence (i.e.,
the ALD cycle) is repeated for anywhere between 300 and 3000
times.
[0239] An alternative to thermal ALD is plasma-enhanced ALD
(PE-ALD). It is generally known in substrate deposition processes
to employ excited species, particularly radicals, to react with
and/or decompose chemical species at the substrate surface to form
the deposited layer. In PE-ALD, the reactant precursor is a plasma,
which contains radicals, ions, electrons and photons. Radical
enhanced plasma ALD is a subset of PE-ALD, which includes the step
of screening out the ions (which can lead to undesired effects)
leaving the radicals to reduce the surface monolayer. FIG. 2
provides a schematic of radical enhanced plasma ALD.
[0240] In one example of PE-ALD in, for example, a BENEQ TFS 200
reactor, a small amount of precursor (0.3-0.5 g) is loaded into an
open-topped precursor boat. This boat is inserted into the source
tube of the reactor. Through internal valving, a pressure of about
140 sccm nitrogen, or other inert gas, is used as the carrier gas
for the precursor, while the reactor is purged with 330 sccm of
nitrogen. A flow of 20 sccm H.sub.2 in 140 sccm nitrogen is used as
the plasma source. In a specific example, a silicon substrate with
its native oxide intact is introduced on a wafer plate through a
load lock. The precursor boat is heated to, for example, about
90.degree. C., and the substrate is heated to, for example, about
225.degree. C. Selection of the appropriate heating temperatures of
the precursor boat and the substrate can be made by any person
skilled in the art, based, at least in part, on the nature of the
precursor and/or substrate. Generally, there is a uniform ramp of
temperature between the precursor boat and the deposition zone to
prevent condensation of the precursor in the apparatus. Preferably,
the plasma employs screens to prevent ions from reaching the
substrate. It should be noted that, in this example, the reaction
chamber always has about 160 sccm of H.sub.2/N.sub.2 flowing
through it, and this gas is not pulsed. The valving is programmed
to deliver a 1 second pulse of precursor followed by 3 seconds of
purging with nitrogen. The plasma pulse is controlled by the plasma
generator, which is programmed to deliver a 6 second pulse of
hydrogen plasma after the precursor purge, followed by 3 seconds of
purging. Typically, this pulse sequence (i.e., the ALD cycle) was
repeated for anywhere between 300 and 3000 times.
[0241] In one embodiment of the present invention, there is
provided a metal deposition process that combines ALD and CVD
processes, for example, in the manufacture of a product having
layers of different metals.
[0242] Also provided herein are systems and compositions comprising
a mono-metallic DAC precursor compound. In specific embodiments the
mono-metallic DAC precursor compound is in an air-tight container,
such as a flame sealed ampule, or a vial, or tube having a cap that
is removably attached to the vial or tube to produce an air-tight
seal. In an alternative embodiment, the mono-metallic precursor
compound is conveniently packaged in a bubbler configured for use
with an ALD tool. Optionally, the DAC precursor compound is
packaged under an inert atmosphere (such as, e.g., nitrogen or
argon gas). In an alternative embodiment, the DAC precursor
compound is in a composition comprising a desiccant, an
anti-oxidant or an additive for inhibiting spontaneous
decomposition of the DAC precursor compound.
[0243] To gain a better understanding of the invention described
herein, the following example is set forth. It should be understood
that these examples are for illustrative purposes only. Therefore,
they should not limit the scope of this invention in any way.
EXAMPLES
Example 1
Reference Example--ALD studies using
1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper(I)
hexamethyldisilazide
[0244] 1,3-Diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper(I)
hexamethyldisilazide (compound of Formula III) was tested as an ALD
precursor. In this example, the thermal ALD tests were performed
using a SUNALE.TM. R series ALD (Picosun, Finland).
[0245] In each test, a small amount of the compound was loaded into
an open-topped precursor boat. This boat was inserted into the
source tube of the reactor and the ALD test was performed as
detailed below.
[0246] Test 1:
[0247] Test 1 was performed using the following conditions: [0248]
Reducing gas: Forming gas, 5% hydrogen in nitrogen [0249]
Temperatures: 110.degree. C. source temperature [0250] 200.degree.
C. reactor temperature [0251] Pulse sequence: 300 cycles of: 0.5
seconds of precursor flow [0252] 5 seconds of nitrogen purge [0253]
4 seconds of forming gas [0254] 10 seconds of nitrogen purge [0255]
Substrate: Si wafer with 50 nm of Al.sub.2O.sub.3
[0256] No change in the appearance of the substrate was observed
after completion of the test, which indicated that no copper film
formed on the substrate.
[0257] Test 2:
[0258] Test 2 was performed using the following conditions: [0259]
Reducing gas: Forming gas, 5% hydrogen in nitrogen [0260]
Temperatures: 120.degree. C. source temperature [0261] 300.degree.
C. reactor temperature [0262] Pulse sequence: 300 cycles of: 1
seconds of precursor flow [0263] 5 seconds of nitrogen purge [0264]
4 seconds of forming gas [0265] 10 seconds of nitrogen purge [0266]
Substrate: Si wafer with 50 nm of Al.sub.2O.sub.3
[0267] No change in the appearance of the substrate was observed
after completion of the test, which again indicated that no copper
film formed on the substrate.
[0268] Test 3:
[0269] Test 3 was performed using the following conditions: [0270]
Reducing gas: Forming gas, 5% hydrogen in nitrogen [0271]
Temperatures: 120.degree. C. source temperature [0272] 350.degree.
C. reactor temperature [0273] Pulse sequence: 300 cycles of: 2
seconds of precursor flow [0274] 5 seconds of nitrogen purge [0275]
4 seconds of forming gas [0276] 10 seconds of nitrogen purge [0277]
Substrate: Si wafer with 50 nm of Al.sub.2O.sub.3
[0278] No change in the appearance of the substrate was observed
after completion of the test, which again indicated that no copper
film formed on the substrate.
[0279] Test 4:
[0280] Test 4 was performed using the following conditions: [0281]
Reducing gas: Forming gas, 5% hydrogen in nitrogen [0282]
Temperatures: 130.degree. C. source temperature [0283] 400.degree.
C. reactor temperature [0284] Pulse sequence: 300 cycles of: 2
seconds of precursor flow [0285] 5 seconds of nitrogen purge [0286]
4 seconds of forming gas [0287] 10 seconds of nitrogen purge [0288]
Substrate: Si wafer with 50 nm of Al.sub.2O.sub.3
[0289] No change in the appearance of the substrate was observed
after completion of the test, which again indicated that no copper
film formed on the substrate.
[0290] Test 5:
[0291] Test 5 was performed using the following conditions: [0292]
Reducing gas: Forming gas, 5% hydrogen in nitrogen [0293]
Temperatures: 160.degree. C. source temperature [0294] 450.degree.
C. reactor temperature [0295] Pulse sequence: 300 cycles of: 2
seconds of precursor flow [0296] 5 seconds of nitrogen purge [0297]
4 seconds of forming gas [0298] 10 seconds of nitrogen purge [0299]
Substrate: Si wafer with 50 nm of Al.sub.2O.sub.3
[0300] No change in the appearance of the substrate was observed
after completion of the test, which again indicated that no copper
film formed on the substrate.
[0301] Test 6:
[0302] Test 6 was performed using the following conditions: [0303]
Reactant gas: H.sub.2O [0304] Temperatures: 160.degree. C. source
temperature [0305] 300.degree. C. reactor temperature [0306] Pulse
sequence: 400 cycles of: 1.5 seconds of precursor flow [0307] 5
seconds of nitrogen purge [0308] 0.4 seconds of water [0309] 10
seconds of nitrogen purge [0310] Substrate: Si wafer with 50 nm of
Al.sub.2O.sub.3
[0311] A slight brown film was observed on the substrate after
completion of the test. Copper was detected in the brown film using
X-ray photoelectron spectroscopy.
[0312] These tests demonstrated that the
1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene copper(I)
hexamethyldisilazide was not successful as an ALD precursor. The
fact that a copper-containing film was generated using water as a
reactant gas suggests that the first five tests failed as a result
of a lack of surface reactivity of the unsaturated compound
monolayer with hydrogen.
Example 2
Synthesis of Mono-Metallic Precursor Compounds with Symmetrically
Substituted sNHC
[0313] A. Synthesis of Symmetrical sNHC-Containing Precursor
Compounds
[0314] Targeted symmetrically substituted precursor compounds 1a,
2a and 3a, were synthesized using a process comprising salt
metathesis. Details of the synthetic steps, from the diamine
starting materials are provided below.
[0315] Materials and Methods
[0316] All manipulations involving a copper-containing reagent or
product were performed in an MBraun Labmaster.TM. 130 Dry box
(mBraun, Stratham, N.H., U.S.A.) under a nitrogen atmosphere. NMR
spectra were recorded on a 400 MHz Bruker AMX spectrometer. NMR
spectra that were measured in CDCl.sub.3 were referenced against
TMS. NMR spectra measured in C.sub.6D.sub.6 or DMSO-d.sub.6 were
referenced against residual protonated solvent.
N,N'-ditertbutyl-ethylenediamine, N,N'-diisopropyl-ethylenediamine,
and N,N'-diethyl-ethylenediamine, triethyl orthoformate were
purchased from Alfa Aesar (VWR, Mississauga, Ontario, Canada).
Sodium tert-butoxide, copper(I) chloride, formic acid were
purchased from Sigma Aldrich Inc. (Oakville, Ontario, Canada).
Hydrochloric acid (11.6 M) was obtained from Anachemia Canada Inc.
(Montreal, Quebec, Canada) and was diluted as necessary. The
diethyl ether adduct of lithium hexamethyldisilazide was prepared
according to Lappert et al. JACS 1983, 105, 302.
[0317] Acetone, diethyl ether, and toluene were purchased from
Caledon Laboratories Ltd. (Georgetown, Ontario, Canada) as reagent
grade. Diethyl ether and toluene were purified from an MBraun
Solvent Purifier System, and stored over 3 A molecular sieves.
Anhydrous tetrahydrofuran and anhydrous pentane were purchased from
Sigma Aldrich Inc. (Oakville, Ontario, Canada) and used as
received.
Synthesis of N,N'-dialkyl ethylenediamines
##STR00013##
[0318] N,N'-diethyl-ethylenediamine dihydrochloride
[0319] N,N'-diethyl-ethylenediamine (4.71 g, 40.5 mmol) was
dissolved in 60 ml of ethanol and cooled in an ice bath. Seven
millilitres of 11.6 M HCl.sub.(aq) was diluted to 20 mL with
ethanol and added dropwise to a stirring solution of the diamine in
ethanol. After the addition of HCl.sub.(aq), the solution was
removed from the ice bath and stirred for 30 minutes while warming
to room temperature ("RT"). Volatiles were evaporated under a flow
of air leaving a colourless solid. This solid was washed with
acetone and then with diethyl ether and dried in air to afford a
quantitative yield. .sup.1H NMR (DMSO-d6): .delta. 9.44 (s, 4H),
.delta. 3.25 (sept, 4H), .delta. 2.97 (q, 4H), .delta. 1.22 (t,
6H).
N,N'-diisopropylethylenediamine dihydrochloride
[0320] The same general procedure used to synthesize
N,N'-diethyl-ethylenediamine dihydrochloride was used to synthesize
N,N'-diisopropylethylenediamine dihydrochloride.
N,N'-diisopropylethylenediamine
[0321] (13.32 g, 92.3 mmol) was dissolved in 100 ml of ethanol.
Next, 31.2 mL of 6 M HCl.sub.(aq) was added dropwise to a stirring
solution of the diamine in ethanol. The resulting solid was
obtained, washed with acetone and dried in an oven at 90.degree. C.
(19.67 g, 98%). .sup.1H NMR (DMSO-d6): .delta. 9.46 (s, 4H),
.delta. 3.35 (s, 4H), .delta. 3.28 (sept, 2H), .delta. 1.26 (d,
12H).
N,N'-ditertbutyl-ethylenediamine dihydrochloride
[0322] The same general procedure detailed above for synthesizing
N,N'-diethyl-ethylenediamine dihydrochloride was used to synthesize
N,N'-ditertbutyl-ethylenediamine dihydrochloride.
N,N'-ditertbutyl-ethylenediamine
[0323] (7.026 g, 40.78 mmol) was dissolved in 100 ml of ethanol.
Next, 30 mL of 3 M HCl.sub.(aq) was added dropwise a stirring
solution of the diamine in ethanol. Volatiles were evaporated under
a flow of air leaving a colourless solid. The yield was
quantitative. The NMR data of the isolated solid matched with the
literature reference in Artensen et al. Tetrahedron 2005, 61,
9710.
Synthesis of 1,3-dialkyl-4,5-dihydro-imidazolium chloride salts
##STR00014##
[0324] 1,3-Diethyl-4,5-dihydro-3H-imidazol-1-ium chloride
[0325] N,N'-diethyl-ethylenediamine dihydrochloride (7.67 g, 40.6
mmol) was suspended in 80 mL of triethyl orthoformate. 12 drops of
formic acid were added and the suspension was refluxed with
stirring at 130.degree. C. for 24 hours. During reflux the
suspension dissolved to give a clear solution. The solution was
cooled to RT and the volatiles were removed in vacuo to afford a
discoloured solid. The solid was dissolved in a minimum of acetone
and 200 mL of diethylether ("Et.sub.2O") was added to precipitate a
solid. The solid was collected by filtration, washed with
Et.sub.2O, and dried under vacuum to afford 5.31 g, 80% yield, of a
hygroscopic solid. .sup.1H NMR (CDCl.sub.3): .delta. 10.05 (s, 1H),
.delta. 4.05 (s, 4H), .delta. 3.71 (q, 4H), .delta. 1.36 (t, 6H).
.sup.13C NMR (CDCl.sub.3): .delta. 158.04, .delta. 47.82, .delta.
43.07, .delta. 12.98.
1,3-Diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride
[0326] The same general procedure used to synthesize
1,3-Diethyl-4,5-dihydro-3H-imidazol-1-ium chloride, except
N,N'-diisopropylethylenediamine dihydrochloride (19.67 g, 90.5
mmol) was suspended in 180 mL of triethyl orthoformate and 20 drops
of formic acid were added before reflux of the resulting
suspension. Following removal of the volatiles from the reaction
mixture, the product was dissolved in 50 mL of acetone and
precipitated by addition of 200 mL of Et.sub.2O (15 g, 88% yield).
.sup.1H NMR (CDCl.sub.3): .delta. 10.16 (s, 1H), .delta. 4.33
(sept, 2H), .delta. 3.96 (s, 4H), .delta. 1.37 (d, 12H). .sup.13C
NMR (CDCl.sub.3): .delta. 162.63, .delta. 50.05, .delta. 38.46,
.delta. 21.76.
1,3-Ditertbutyl-4,5-dihydro-3H-imidazol-1-ium chloride
[0327] The same general procedure used to synthesize
1,3-Diethyl-4,5-dihydro-3H-imidazol-1-ium chloride was used to
synthesize 1,3-Ditertbutyl-4,5-dihydro-3H-imidazol-1-ium chloride,
except N,N'-ditertbutyl-ethylenediamine dihydrochloride (5.00 g,
20.39 mmol) was suspended in 40 mL of triethyl orthoformate and 10
drops of formic acid were added before reflux of the resulting
suspension. Reflux was maintained for 72 h. Volatiles were removed
in vacuo to afford a discoloured solid (4.20 g, 94.2%). .sup.1H NMR
(DMSO-d.sub.6): .delta. 8.19 (s, 1H), .delta. 3.93 (s, 4H), .delta.
1.36 (s, 18H). .sup.13C NMR (CDCl.sub.3): .delta. 154.20, .delta.
57.11, .delta. 45.22, .delta. 28.15.
Synthesis of 1,3-dialkyl-imidazolin-2-ylidene copper chloride
salts
##STR00015##
[0328] 1,3-diethyl-imidazolin-2-ylidene copper chloride
[0329] 1,3-Diethyl-4,5-dihydro-3H-imidazol-1-ium chloride (2.875 g,
17.7 mmol) was suspended in 50 mL of tetrahydrofuran ("THF"). CuCl
(1.804 g, 18.2 mmol) was added and the resulting cloudy solution
was stirred for 30 minutes. Sodium tert-butoxide (1.751 g, 18.2
mmol) was dissolved in 20 mL of THF and added dropwise to the
stirring solution. Stirring was continued overnight. The cloudy
solution was filtered through Celite.TM. to remove the NaCl
precipitate. Volatiles of the clear filtrate were removed in vacuo
until a light brown solid remained. The crude product was of
sufficient purity to proceed without purification (3.78 g, 95.0%).
.sup.1H NMR (CDCl.sub.3): .delta. 3.61 (q, 4H), .delta. 3.60 (s,
4H), .delta. 1.23 (t, 6H). .sup.13C NMR (CDCl.sub.3): .delta.
198.81, .delta. 47.93, .delta. 45.33, .delta. 14.10.
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper
chloride
[0330] The same general procedure as above was used.
1,3-Diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride (4.404 g,
23.1 mmol) was suspended in 100 mL THF. CuCl (2.20, 22.2 mmol) and
sodium tert-butoxide (2.260 g, 23.5 mmol) in 45 mL of THF were
used. The solid was washed with pentane until the washings were
colourless and then dried under vacuum (4.989 g, 88.3%). .sup.1H
NMR (CDCl.sub.3): .delta. 4.39 (sept, 2H), .delta. 3.51 (s, 4H),
.delta. 1.24 (d, 12H). .sup.13C NMR (CDCl.sub.3): .delta. 197.42,
.delta. 51.80, .delta. 42.78, .delta. 21.15.
1,3-ditertbutyl-4,5-dihydro-imidazolin-2-ylidene copper
chloride
[0331] 1,3-Ditertbutyl-4,5-dihydro-3H-imidazol-1-ium chloride
(1.745 g, 7.98 mmol) was suspended in 30 mL of THF. Sodium
tert-butoxide (0.766 g, 7.97 mmol) was dissolved in 20 mL of THF
and added dropwise to the suspension and stirred for 30 min. CuCl
(0.789, 7.97 mmol) was added and stirring continued overnight. The
cloudy solution was filtered through Celite.TM. to remove the NaCl
precipitate. Volatiles of the clear filtrate were removed in vacuo
to afford a slightly pink solid (2.195 g, 97.8%). .sup.1H NMR
(CDCl.sub.3): .delta. 3.54 (s, 4H), .delta. 1.53 (s, 18H). .sup.13C
NMR (CDCl.sub.3): .delta. 197.58, .delta. 55.12, .delta. 45.63,
.delta. 30.80.
Synthesis of 1,3-dialkyl-imidazolin-2-ylidene copper
hexamethyldisilazide
##STR00016##
[0332] 1,3-diethyl-imidazolin-2-ylidene copper hexamethyldisilazide
(1a)
[0333] 1,3-diethyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
(0.938 g, 4.15 mmol) was dissolved in 40 mL of toluene in a flask.
The flask was wrapped in aluminum foil and then cooled to
-35.degree. C. in a freezer. The diethyl ether adduct of lithium
hexamethyldisilazide (1.006 g, 4.17 mmol) was dissolved in 20 mL of
toluene and added dropwise to the -35.degree. C. solution as it
gradually warmed to room temperature. Stirring was continued
overnight. The cloudy solution was filtered and then volatiles were
removed from the clear filtrate under reduced pressure to afford a
slightly discoloured liquid. This liquid was purified by
distillation from 130 to 150.degree. C. at 40 mtorr to obtain 1.287
g, 88%, of a colourless liquid. .sup.1H NMR (C.sub.6D.sub.6):
.delta. 3.23 (q, 4H), .delta. 2.37 (s, 4H), .delta. 0.76 (t, 6H),
.delta. 0.58 (s, 18H). .sup.13C NMR (C.sub.6D.sub.6): .delta.
201.26, .delta. 47.11, .delta. 44.81, .delta. 13.83, .delta.
7.22.
1,3-diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide
(2a)
[0334] The same reaction as above was used substituting
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
(4.456 g, 17.52 mmol) dissolved in 130 mL of toluene and the
diethyl ether adduct of lithium hexamethyldisilazide (4.248 g, 17.6
mmol) dissolved in 70 mL of toluene. Volatiles were removed to
afford a solid which was purified by sublimation at 90.degree. C.
and 35 mtorr using a dry ice/acetone cold finger (6.322 g, 95%).
.sup.1H NMR (C.sub.6D.sub.6): .delta. 4.48 (sept, 2H), .delta. 2.48
(s, 4H), .delta. 0.80 (d, 12H), .delta. 0.57 (s, 18H). .sup.13C NMR
(C.sub.6D.sub.6): .delta. 200.39, .delta. 51.15, .delta. 41.86,
.delta. 20.67, .delta. 7.21.
1,3-ditertbutyl-imidazolin-2-ylidene copper hexamethyldisilazide
(3a)
[0335] The same reaction as above was used substituting
1,3-ditertbutyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
(0.489 g, 1.74 mmol) dissolved in 30 mL of toluene and the diethyl
ether adduct of lithium hexamethyldisilazide (0.420 g, 1.74 mmol)
dissolved in 10 mL of toluene. Volatiles were removed in vacuo to
afford an off-white solid which was redissolved in 3 mL of pentane
and held at -35.degree. C. for 24 hours. The solution was decanted
to afford colourless needle crystals (0.610 g, 86.4%). .sup.1H NMR
(C.sub.6D.sub.6): .delta. 2.56 (s, 4H), .delta. 1.32 (s, 18H),
.delta. 0.56 (s, 18H). .sup.13C NMR (C.sub.6D.sub.6). .delta.
201.50, .delta. 55.04, .delta. 45.24, .delta. 30.78, .delta.
6.87.
[0336] B: Modified Synthesis of sNHC-Containing Precursor
Compound
[0337] The following procedure details a modified synthesis of the
sNHC-containing precursor compounds. This process removes an
additional isolation step (of the intermediate dialkylamine
dihydrochloride) in making the starting 1,3-dialkyl-imidazolium
salt prior to the addition of NaN(TMS).sub.2.
Step 1: Preparation of 1,3-dialkyl-imidazolium salts
[0338] In comparison to the procedure detailed above in Example 2,
this procedure reduces the number of isolation steps by one (4
steps in the above synthesis; 3 in this sequence), and was found to
improve upon the yield of the alkyl-imidazolium salt,
1,3-diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride (i.e., from
about 78% to about 93%).
##STR00017##
[0339] To a nitrogen purged flask was added 2.299 g (15.94 mmol) of
N,N'-diisopropylethylenediamine, which was diluted in 35 mL of
trimethyl orthoformate. The solution was cooled to 0.degree. C.
before 8 mL of HCl (4.0 M in 1,4-dioxane, 32.0 mmol) was added
dropwise, resulting in a thick white slurry. Once the addition of
HCl was finished the solution was gradually warmed to room
temperature and stirred vigorously for 2 hours. After this time, 3
drops of formic acid were added to the suspension. A condenser was
attached to the reaction flask, and the suspension was heated to
100.degree. C. for a period of 16 hours. The slurry gradually
dissolved in heated trimethyl orthoformate, resulting in a clear
orange solution. After the 16 hour reaction period, the solution
was cooled to room temperature.
[0340] To isolate the product, 150 mL of heptanes were added to the
orange solution, causing a dark orange oil to separate from the
solution. The top portion was decanted to isolate the orange oil.
In order to precipitate the product from the oil, 30 mL of toluene
was added and the mixture was concentrated under vacuum.
Approximately 5 mL were removed before a solid material
precipitated from solution. The remaining solvent was then decanted
and the solid dried under vacuum, yielding 2.829 g (14.83 mmol,
93%), of the product, 1,3-diisopropyl-4,5-dihydro-3H-imidazol-1-ium
chloride.
Step 2: Preparation of 1,3-dialkyl-imidazolin-2-ylidene copper
chloride salts
##STR00018##
[0342] Under an inert atmosphere, 0.6613 g (3.47 mmol) of
1,3-diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride were added
to a 250 mL round bottomed flask. To the same flask was added 0.378
g (3.81 mmol) of CuCl. The reagents were suspended in 50 mL of
tetrahydrofuran and cooled to 0.degree. C. A KOtBu solution (0.428
g, 3.81 mmol in 20 mL of THF) was added dropwise to the cooled
solution of 1,3-diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride
with CuCl, resulting in the formation of a green suspension. The
suspension was kept cooled until the addition of base was
completed. Once finished, the combined solution was gradually
warmed to room temperature and stirred vigorously for 24 hours. The
reaction was filtered over a layer of Celite to remove the
insoluble material. The
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
was then isolated by the addition of hexanes (approximately 2
volume equivalents of hexanes). The supernatant solution was
decanted to isolate an off-white powder. The powder was pumped to
dryness under vacuum to yield 0.705 g (2.77 mmol, 80%) of
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper
chloride.
Step 3: Preparation of 1,3-dialkyl-imidazolin-2-ylidene copper
hexamethyldisilazide
##STR00019##
[0344] Under inert atmosphere, 9.0805 g (35.7 mmol) of
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
was dissolved in 250 mL of dry toluene. In a separate flask, 6.55 g
(35.7 mmol) of NaN(TMS).sub.2 were dissolved in 100 mL of dried
toluene. The solution containing
1,3-diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper chloride
was cooled to 0.degree. C. and then the amide solution was added
dropwise over the course of one hour. The combined solution was
gradually warmed to room temperature once the addition was
completed, and the solution was stirred for 24 hours. The initially
green coloured solution became a dark brown solution as the
reaction proceeded. After 24 hours, the solution was filtered under
inert atmosphere through a layer of Celite. The filtrate was clear
and colourless, and collected in a nitrogen purged flask. The
insoluble material was washed with 3.times.20 mL of toluene. The
washings were combined with the filtrate. The solvent was removed
from the combined washings and filtrate, yielding 11.3631 g (30
mmol, 84%) of product, 1,3-diisopropyl-imidazolin-2-ylidene copper
hexamethyldisilazide (2a).
Example 3
Synthesis of Mono-Metallic Precursor Compounds with Asymmetrically
Substituted sNHC
[0345] The targeted asymmetric carbene copper amide complexes 12a,
13a and 14a are depicted below,
##STR00020##
where TMS is a trimethylsilyl group. These compounds were prepared
according to the procedure detailed below.
[0346] Materials and Methods
[0347] NMR spectra were recorded on a Varian 400-MR NMR
spectrometer (Agilent, Mississauga, Ontario, Canada). All NMR
spectra are referenced against residual protonated solvent.
2-(tert-butylamino)ethanol, methylamine, ethylamine, formic acid,
and copper (I) chloride were obtained from Sigma Aldrich Inc.
(Oakville, Ontario, Canada). Hydrochloric acid was obtained from
Fisher Scientific (Ottawa, Ontario, Canada) and was diluted to 6M
in water. Thionyl chloride, potassium tert-butoxide, and sodium
bis(trimethylsilyl)amide were obtained from Alfa Aesar (VWR,
Mississauga, Ontario, Canada).
[0348] Dichloromethane, acetone, and diethyl ether was obtained
from Fisher Scientific. Anhydrous ethanol was obtained from
Commercial Alcohols Inc (Brampton, Ontario, Canada).
Tetrahydrofuran and toluene were obtained from EMD Chemicals
(Gibbstown, N.J., USA) and purified using a VAC Solvent Purifier
(Vacuum Atmospheres Company, Hawthorne, Calif., USA).
Synthesis of N-tert-butyl N'-alkyl ethylenediamines
##STR00021##
[0350] The diamines were synthesized according to a literature
procedure (Morley, J. S. ICI LTD (1963) Substituted
Ethylenediamines, GB919177 (A)) and characterized from data
outlined by Denk. (Denk, M. K.; Hezarkhani, A.; Zheng. F. L. Eur.
J. Inorg. Chem. 2007, 3527-3534). After isolation of the diammonium
salts all manipulations were carried out under inert atmosphere
(Nitrogen--99.99%, supplied by Air Liquide, Toronto, Ontario,
Canada).
Synthesis of 1-tert-butyl-3-alkyl-imidazolium salts
##STR00022##
[0352] Asymmetric imidazolium salts have not been previously
reported, however, a modified version of a literature procedure
(Arentsen, K.; Caddick, S.; Cloke, G. N. Tetrahedron, 2005, 61,
9710-9715) was found to be useful in the synthesis of these
intermediates (outlined in the scheme above).
3-(tert-butyl)-1-methyl-4,5-dihydro-imidazol-3-ium chloride
[0353] White solid, 25%. .sup.1H NMR (CDCl.sub.3): 10.26 ppm (s,
1H), 3.91 ppm (s, 4H), 3.45 ppm (s, 3H), 1.48 ppm (s, 9H).
3-(tert-butyl)-1-ethyl-4,5-dihydro-imidazol-3-ium chloride
[0354] White solid, 48%. .sup.1H NMR (CDCl.sub.3): 10.13 ppm (s,
1H), 3.89 ppm (s, 4H), 3.86 ppm (q, 2H), 1.30 ppm (s, 9H), 1.28 ppm
(t, 3H). .sup.13C NMR (CDCl.sub.3): 157.2 ppm, 56.8 ppm, 47.4 ppm,
45.1 ppm, 43.2 ppm, 28.3 ppm, 13.1 ppm.
3-(tert-butyl)-1-isopropyl-4,5-dihydro-imidazol-3-ium chloride
[0355] White solid, 48%. .sup.1H NMR (CDCl.sub.3): 10.09 ppm (s,
1H), 4.73 ppm (m, 1H), 3.89 ppm (s, 4H), 1.33 ppm (s, 9H), 1.31 ppm
(d, 6H).
Synthesis of 1-tert-butyl-3-alkyl-imidazolidin-2-ylidene copper (I)
chloride compounds
##STR00023##
[0356] 1-tert-Butyl-3-ethyl-imidazolidin-2-ylidene copper (I)
chloride
[0357] 1.8816 g (9.87 mmol) of
3-tert-butyl-1-ethyl-4,5-dihydro-imidazol-3-ium chloride was
combined with 0.9913 g (10.01 mmol) of CuCl in a 250 mL Schlenk
flask, and dissolved in 100 mL of THF. In a separate flask was
added 1.1106 g (9.90 mmol) of potassium tert-butoxide, which was
dissolved in 50 mL of tetrahydrofuran. Each solution was stirred
for 30 minutes before the potassium tert-butoxide solution was
transferred dropwise via cannula to the CuCl/imidazolium chloride
solution. The resultant mixture gradually became dark brown over
the course of an hour. Mixing was continued at room temperature for
24 hours. The brown suspension was filtered through Celite.TM. over
a medium porosity glass frit. The insoluble material was washed
with 4.times.10 mL of THF. The washings were combined with the
brown filtrate and the solvent was removed under vacuum, yielding a
brown oil. A brown powder was isolated after diluting the oil in 20
mL of toluene followed by the addition of 30 mL of hexanes. The
supernatant solution was decanted to yield 1.989 g (7.85 mmol, 80%
yield) of 1-tert-Butyl-3-ethyl-imidazolidin-2-ylidene copper (I)
chloride as a brown solid. .sup.1H NMR (C.sub.6D.sub.6): 3.25 ppm
(q, 2H), 2.82 ppm (t, 3H), 2.63 ppm (t, 3H), 1.19 ppm (s, 9H), 0.77
ppm (t, 3H). .sup.13C NMR (C.sub.6D.sub.6): 198.5 ppm, 54.5 ppm,
46.7 ppm, 46.3 ppm, 41.7 ppm, 30.3 ppm, 13.9 ppm.
1-tert-Butyl-3-methyl-imidazolidin-2-ylidene copper (I)
chloride
[0358] 1-tert-Butyl-3-methyl-imidazolidin-2-ylidene copper (I)
chloride was synthesized from
3-(tert-butyl)-1-methyl-4,5-dihydro-imidazol-3-ium chloride using
the same method as set out above for the 3-ethyl compound. The
product was a white solid with a yield of 65.4%. .sup.1H NMR
(C.sub.6D.sub.6): 3.65 ppm (t, 3H), 3.48 ppm (t, 3H), 3.26 ppm (s,
3H), 1.50 ppm (s, 9H). .sup.13C NMR (CDCl.sub.3): 198.7 ppm, 54.9
ppm, 50.3 ppm, 46.9 ppm, 38.8 ppm, 30.6 ppm.
1-tert-Butyl-3-isopropyl-imidazolidin-2-ylidene copper (I)
chloride
[0359] 1-tert-Butyl-3-isopropyl-imidazolidin-2-ylidene copper (I)
chloride was synthesized from
3-(tert-butyl)-1-isopropyl-4,5-dihydro-imidazol-3-ium chloride
using the same method as set out above for 3-ethyl compound. The
product was a white solid, with a yield of 92%. .sup.1H NMR
(C.sub.6D.sub.6): 4.56 ppm (m, 1H), 3.59 ppm (t, 3H), 3.40 ppm (t,
3H), 1.46 ppm (s, 9H), 1.20 ppm (d, 6H).
Synthesis of
bis(trimethylsilyl)amino-1-tert-butyl-3-alkyl-imidazolidin-2-ylidene
copper (I)
##STR00024##
[0360] 1-tert-butyl-3-ethyl-imidazolidin-2-ylidene copper (I)
hexamethyldisilazide (13a)
[0361] 0.906 g (3.58 mmol) of
1-tert-butyl-3-ethyl-imidazolidin-2-ylidene copper (I) chloride was
dissolved in 60 mL of toluene and cooled to 0.degree. C. In a
separate flask was added 0.656 g (3.58 mmol) of sodium
bis(trimethylsilyl)amide which was dissolved in 60 mL of toluene.
The bis(trimethylsilyl)amide solution was added dropwise to the
solution of the imidazolidin-2-ylidene copper chloride compound via
cannula. The resultant mixture was gradually warmed to room
temperature and stirred for 60 hours. The product suspension was
filtered over a layer of Celite.TM. through a medium porosity glass
frit. The insoluble fraction was washed with 3.times.15 mL of
toluene. The washings were combined with the colourless filtrate,
and the solvent was removed under vacuum affording 0.9513 g (2.52
mmol, 70.3% yield) of 13a as an amber oil. .sup.1H NMR
(C.sub.6D.sub.6): 3.40 ppm (q, 2H), 2.54 ppm (t, 3H), 2.33 ppm (t,
3H), 1.21 ppm (s, 9H), 0.79 ppm (t, 3H), 0.56 ppm (s, 18H).
.sup.13C NMR (C.sub.6D.sub.6): 201.0 ppm, 54.5 ppm, 46.3 ppm, 46.2
ppm, 45.9 ppm, 30.4 ppm, 13.8 ppm, 7.1 ppm.
1-tert-butyl-3-methyl-imidazolidin-2-ylidene copper (I)
hexamethyldisilazide (12a)
[0362] 1-tert-butyl-3-methyl-imidazolidin-2-ylidene copper (I)
hexamethyldisilazide 12a was synthesized from
1-tert-Butyl-3-methyl-imidazolidin-2-ylidene copper (I) chloride
using the same method as set out above for the synthesis of
compound 13a. The reaction afforded 12a as a brown oil (44% yield).
.sup.1H NMR (C.sub.6D.sub.6): 2.75 ppm (s, 3H), 2.53 ppm (t, 3H),
2.19 ppm (t, 3H), 1.20 ppm (s, 9H), 0.56 ppm (s, 18H). .sup.13C NMR
(C.sub.6D.sub.6): 201.5 ppm, 54.5 ppm, 49.3 ppm, 46.2 ppm, 38.2
ppm, 30.4 ppm, 7.2 ppm.
1-tert-butyl-3-isopropyl-imidazolidin-2-ylidene copper (I)
hexamethyldisilazide (14a)
[0363] 1-tert-butyl-3-isopropyl-imidazolidin-2-ylidene copper (I)
hexamethyldisilazide (14a) was synthesized from
1-tert-Butyl-3-isopropyl-imidazolidin-2-ylidene copper (I) chloride
using the same method as set out above for the synthesis of
compound 13a. The reaction afforded 14a as a colourless solid (86%
yield). .sup.1H NMR (C.sub.6D.sub.6): 4.78 ppm (m, 1H), 2.58 ppm
(t, 3H), 2.42 ppm (t, 3H), 1.22 ppm (s, 9H), 0.81 ppm (d, 6H), 0.56
ppm (s, 18H). .sup.13C NMR (C.sub.6D.sub.6): 200.7 ppm, 54.5 ppm,
52.3 ppm, 45.3 ppm, 41.4 ppm, 30.3 ppm, 20.6 ppm, 7.1 ppm.
Example 4
X-Ray Structural Analysis of Metal Precursor Compounds
[0364] X-ray structural analysis was performed for compound 2c
according to the following method.
[0365] Crystals of the compound were selected and mounted on
plastic mesh using viscous oil flash-cooled to the data collection
temperature. Data were collected on a Bruker-AXS APEX CCD
diffractometer with graphite-monochromated Mo-K.alpha. radiation
(.lamda.=0.71073 .ANG.). Unit cell parameters were obtained from 60
data frames, 0.3.degree. .omega., from three different sections of
Ewald sphere. The systematic absences in the data and the unit cell
parameters were consistent to C2/c and Cc for 2c. In the non-unique
systematic absence cases, the centrosymmetric space group option
yielded chemically reasonable and computationally stable results of
refinement. The data-sets were treated with SADABS absorption
corrections based on redundant multiscan data (Sheldrick, G. M.
2008. Acta Cryst. A64, 112-122). The structure was solved using
direct methods and refined with full-matrix, least-squares
procedures on F2. The compound molecule is located on a two-fold
rotation axis. All non-hydrogen atoms were refined with anisotropic
displacement parameters. All hydrogen atoms were treated as
idealized contributions. Atomic scattering factors are contained in
the SHELXTL 6.12 program library (Sheldrick, G. M., 2008. Acta
Cryst. A64, 112-122).
[0366] An ORTEP drawing of the X-ray structure is depicted in FIG.
7.
Example 5
Thermogravimetric Analysis of Metal Precursor Compounds
[0367] Vapour pressures of a variety of symmetrical and
unsymmetrical copper precursor compounds were measured on a TA
Instruments Q50 thermogravimetric (TG) analyser located in an
MBraun Labmaster 130 Dry box under a nitrogen atmosphere. The TG
was run in a stepped isotherm using the following sequence: [0368]
Ramp 40.00.degree. C./min to 110.00.degree. C. [0369] Isothermal
for 10.00 min [0370] Ramp 40.00.degree. C./min to 120.00.degree. C.
[0371] Isothermal for 10.00 min [0372] Ramp 40.00.degree. C./min to
130.00.degree. C.
[0373] Isothermal for 10.00 min
[0374] Ramp 40.00.degree. C./min to 140.00.degree. C.
[0375] Isothermal for 10.00 min
[0376] Ramp 40.00.degree. C./min to 150.00.degree. C.
[0377] Isothermal for 10.00 min
[0378] Ramp 40.00.degree. C./min to 160.00.degree. C.
[0379] Isothermal for 10.00 min
[0380] Ramp 40.00.degree. C./min to 170.00.degree. C.
[0381] Isothermal for 10 min
[0382] Ramp 40.00.degree. C./min to 180.00.degree. C.
[0383] Isothermal for 10 min
[0384] Ramp 40.00.degree. C./min to 190.00.degree. C.
[0385] Isothermal for 10.0 min
[0386] Ramp 40.00.degree. C./min to 200.00.degree. C.
[0387] Isothermal for 10.0 min
[0388] Ramp 10.00.degree. C./min to 600.00.degree. C.
[0389] The slope was determined for each isotherm interval, and if
the data was linear for that interval, that was used as the
".DELTA.m/.DELTA.t" value for that temperature. The pressure was
calculated using the Langmuir equation following the method of
Umarji [G. V. Kunte, S. A. Shivashanker, A. M. Umarji Meas. Sci.
Tech. 2008, 19, 025704] for estimation of vapour pressure. Benzoic
acid was used as a standard to determine the .alpha. coefficient of
the Langmuir equation (i.e., the Langmuir adsorption constant), and
copper bis (2,2,6,6-tetramethyl-3,5-heptadionate)
("Cu(tmhd).sub.2") was used as a benchmark to demonstrate the
method's validity.
[0390] The results from vapour testing of four symmetrical copper
precursor compounds and three unsymmetrical copper precursor
compound are provided in the Table 1 and depicted in FIGS. 8 and 9.
The compound, Cu(tmhd).sub.2, was used as a control as it is a
known CVD precursor. The structure of Cu(tmhd).sub.2 is shown
below:
##STR00025##
TABLE-US-00001 TABLE 1 Vapour Testing of Symmetrical and
Unsymmetrical Copper Precursor Compounds Temperature (.degree. C.)
for Compound 1 Torr of Pressure Cu(tmhd).sub.2 155
Et.sub.2--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (1a) 134
.sup.iPr.sub.2--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (2a) 131
.sup.tBu.sub.2--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (3a) 153
Me.sub.2.sup.tBu.sub.2--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (4a) 144
Me.sup.tBu--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (12a) 140
Et.sup.tBu--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (13a) 137
.sup.iPr.sup.tBu--sNHC--Cu(I)--N(SiMe.sub.3).sub.2 (14a) 132
[0391] In similar studies performed using similar copper-containing
compounds that include an unsaturated NHC, the present inventors
found that the unsaturated NHC compounds tested decomposed during
the most basic thermogravimetric analysis (i.e., as temperature was
increased 10.degree. C. per minute up to 400.degree. C.).
[0392] In contrast, the results provided herein, demonstrate good
thermal stability and volatility for the copper precursor compounds
that include the sNHC. In addition, the copper precursor compounds
tested were found to have vapour pressure properties superior to
those of Cu(tmhd).sub.2. First, the slopes of the vapour pressure
lines are more shallow for the copper precursor compounds described
herein than for Cu(tmhd).sub.2, which indicates that these
compounds have higher vapour pressures at lower temperatures than
Cu(tmhd).sub.2. Furthermore, all of the sNHC precursor compounds
tested volatised to 1 Torr of pressure at a lower temperature than
did Cu(tmhd).sub.2. These characteristics are desirable for
successful ALD precursors.
Example 6
Thermogravimetric Analysis of Compounds Containing Saturated and
Unsaturated N-Heterocyclic Diaminocarbene Moieties
[0393] TG analysis was performed on a TA Instruments Q50
thermogravimetric (TG) analyser located in an MBraun Labmaster 130
Dry box under a nitrogen atmosphere (99.999% at a flow rate of 100
mL/min). During testing the furnace was heated at 10.degree. C./min
from 30 to 600.degree. C. Samples of the compounds to be studied
were provided in platinum pans with diameters of 1 cm. The mass of
each sample tested was within the range of from about 10 to about
30 mg. The mass ("weight") of the sample was obtained as the
temperature was increased and plotted.
[0394] The results are provided in FIGS. 10-21. The residual mass
(% mass that remains in the platinum pan after 600.degree. C.) is
displayed in bottom right corner of each graph.
[0395] FIG. 10 shows a weight loss curve for an unsaturated
N-heterocyclic diaminocarbene-containing copper compound
(1,3-di-tert-butyl-imidazol-2-ylidene copper hexamethyldisilazide).
It is clear that this compound is thermally unstable since there
are two weight loss events and a high residual mass of 14.7%, which
indicate decomposition.
[0396] FIG. 11 shows an improvement of volatility and thermal
stability of an unsaturated N-heterocyclic
diaminocarbene-containing copper compound
(1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene copper
hexamethyldisilazide; the compound of Formula III). This was
achieved by chemically modifying the unsaturated bond with methyl
groups. The residual mass was 7.4% which again indicates
decomposition of the compound. This suggests that this compound
will not be useful in ALD. The data obtained using the two
unsaturated compounds suggested that the unsaturated bond is
undesirable in an ALD precursor.
[0397] FIGS. 12-21 show weight loss curves for various
sNHC-containing copper compounds.
[0398] The results obtained from the saturated analogue of
1,3-di-tert-butyl-imidazol-2-ylidene copper hexamethyldisilazide
are depicted in FIG. 14. It is clear, from this direct comparison,
that the sNHC-containing compound is volatile and has better
thermal stability then the unsaturated analogue. The residual mass
of 1.4% shows there was negligible decomposition of the compound
during the experiment.
[0399] The results obtained from
1,3-diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide
(2a) are depicted in FIG. 13. This compound is not a full analogue
of the unsaturated 1,3-diisopropyl-imidazol-2-ylidene compound
referred to above, since it does not comprise the 4,5-dimethyl
substituents. However, even without these stabilizing substituents,
the saturated analogue was found to exhibit better volatility and
thermal stability. The residual mass of 1.6% shows there was
negligible decomposition of the compound during the experiment.
[0400] These examples show that a saturated NHC Cu compound has
superior behaviour with respect to volatility and thermal stability
than an unsaturated NHC Cu compound. Furthermore, all the
sNHC-containing copper compounds tested had a residual mass of less
than 7.4% or, more particularly, less than 5%, which was indicative
of good volatility.
[0401] FIGS. 19 and 21 show weight loss curves for sNHC-containing
silver and gold compounds, respectively. These compounds also show
good volatility since the residual masses were lower than the metal
content of the compound. In order to confirm the usefulness of
these compounds in ALD, further tests were performed.
[0402] A single isothermal experiment was performed using
1,3-diisopropyl-imidazolin-2-ylidene silver hexamethyldisilazide
(2b) whereby the furnace was heated 10.degree. C./min to a low
temperature (140.degree. C.) and held for several hours (see FIG.
20A). The residual mass from this experiment was 10.15%, less than
half the residual mass observed in the weight loss curve analysis,
demonstrating that more of the compound volatilised at hold
temperature rather than decomposing in the pan.
[0403] With respect to 1,3-diisopropyl-imidazolin-2-ylidene gold
hexamethyldisilazide (2c), 3 g of this compound was readily
purified by sublimation, which also provides evidence of good
volatility.
[0404] Another single isothermal experiment was performed using
1,3-diisopropyl-imidazolin-2-ylidene gold hexamethyldisilazide (2c)
whereby the furnace was heated 10.degree. C./min to a low
temperature (140.degree. C.) and held for several hours (see FIG.
20B). The residual mass from this experiment was 17.66%,
significantly less than the residual mass observed in the weight
loss curve analysis, demonstrating that a significant amount of the
compound volatilised at hold temperature rather than decomposing in
the pan.
[0405] These studies, thus, provided additional evidence of thermal
stability and volatility of the sNHC-containing silver and gold
compounds at the lower temperatures.
Example 7
Metal Deposition Saturation Curve
[0406] 1,3-Diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper (I)
hexamethyldisilazide (2a) was used in the preparation of a
saturation curve to demonstrate an example of successful copper
film deposition on a substrate.
[0407] In this example, the copper films were deposited by ALD
using an ALD system TFS 200 (BENEQ, Finland) employing
capacitively-coupled plasma.
[0408] A small amount of precursor (0.3-0.5 g) was loaded into an
open-topped precursor boat. This boat was inserted into the source
tube of the reactor. A flow of 20 sccm H.sub.2 in 140 sccm argon
was used as the plasma source. A silicon substrate with its native
oxide intact was introduced on a 200 mm wafer plate through a load
lock. The plasma used was a capacitively coupled plasma using
screens to prevent ions from reaching the substrate. It should be
noted that the reaction chamber always had 160 sccm of
H.sub.2/N.sub.2 flowing through it, which was not pulsed.
[0409] Pulse length was determined by the ALD deposition
experiment. Thus, each data point on the saturation curve can be
considered a separate deposition experiment.
[0410] The saturation curve obtained using
1,3-isopropylimidazolin-2-ylidene copper(I) hexamethyldisilazide
(2a) is shown in FIG. 22. A description of the process used for
each point on the curve is provided below.
[0411] Film thickness was determined by modelling the K-ratios from
the energy dispersive X-ray (EDS) spectrum measured using an Oxford
INCA 350 energy dispersive X-ray microanalysis system equipped on
the scanning electron microscope (SEM). Thickness was modelled
using GMRFILM, a research grade, shareware DOS program for thin
film analysis (created by Richard Waldo of General Motors Research
Labs; Waldo, R. A., Militello, M. C. and Gaarenstroom, S. W.,
Surface and Interface Analysis 20: 111-114 (1993)). Growth rate was
calculated by dividing the measured thickness by the number of
cycles.
[0412] An image of the thickest film profile (FIG. 23) was
collected using a Hitachi S-4800 field emission scanning electron
microscope (SEM) and the following conditions:
[0413] Accelerating Voltage: 5000 Volt
[0414] Magnification: 220,000.times.
[0415] Working Distance: 3 mm
[0416] The film was measured at 35.+-.2 nm thickness over nine
images. The correction of 350/205.2=1.71 has been applied to the
saturation curve values measured by EDS. This gives a film (mass)
density of 5.24 gcm.sup.-3 compared to 8.96 gcm.sup.-3 for bulk
copper.
[0417] At point 1 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0418] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0419] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0420] Carrier gases: 330 sccm nitrogen to the reactor
[0421] 220 sccm nitrogen to the tool [0422] Pulse sequence: 600
cycles of: 1 seconds of precursor flow [0423] 3 seconds of nitrogen
purge [0424] 6 seconds of hydrogen plasma [0425] 3 seconds of
nitrogen purge
[0426] At this point no copper could be detected by EDS or seen by
SEM.
[0427] At point 2 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0428] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0429] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0430] Carrier gases: 330 sccm nitrogen to the reactor
[0431] 220 sccm nitrogen to the tool [0432] Pulse sequence: 500
cycles of: 2 seconds of precursor flow [0433] 3 seconds of nitrogen
purge [0434] 6 seconds of hydrogen plasma [0435] 3 seconds of
nitrogen purge
[0436] Following this run no copper could be detected by EDS.
However, the SEM showed nanocrystals that were determined to be a
heavy element by using backscattered electrons, which, given the
reagents used, was considered to be copper.
[0437] FIGS. 24 and 25 show micrographs of the 0 .ANG. film
produced at point 2. The image shown in FIG. 24 was obtained using
a Hitachi S-4800 field emission SEM (Accelerating Voltage: 20000
Volt; Magnification: 120000.times.; Working Distance: 14.7 mm). The
image shown in FIG. 25 was obtained using a Hitachi S-4800 field
emission SEM (Accelerating Voltage: 3000 Volt; Magnification:
100000.times.; Working Distance: 4.4 mm). This image is made by
backscattered electrons, and shows the nanocrystals to be composed
of a heavy element.
[0438] At point 3 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0439] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0440] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0441] Carrier gases: 330 sccm nitrogen to the reactor
[0442] 220 sccm nitrogen to the tool [0443] Pulse sequence: 800
cycles of: 3 seconds of precursor flow [0444] 3 seconds of nitrogen
purge [0445] 6 seconds of hydrogen plasma [0446] 3 seconds of
nitrogen purge
[0447] The film at point 3 on the saturation curve was
approximately 106 .ANG. thick.
[0448] At point 4 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0449] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0450] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0451] Carrier gases: 330 sccm nitrogen to the reactor
[0452] 220 sccm nitrogen to the tool [0453] Pulse sequence: 700
cycles of: 4 seconds of precursor flow [0454] 3 seconds of nitrogen
purge [0455] 6 seconds of hydrogen plasma [0456] 3 seconds of
nitrogen purge
[0457] FIGS. 26 and 27 show micrographs of the approximately 141
.ANG. film produced at point 4. The image shown in FIG. 26 was
obtained using a Hitachi S-4800 field emission SEM (Accelerating
Voltage: 20000 Volt; Magnification: 50000.times.; Working Distance:
14.8 mm). The image shown in FIG. 27 was obtained using a Hitachi
S-4800 field emission SEM (Accelerating Voltage: 20000 Volt;
Magnification: 120000.times.; Working Distance: 14.8 mm).
[0458] At point 5 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0459] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0460] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0461] Carrier gases: 330 sccm nitrogen to the reactor
[0462] 220 sccm nitrogen to the tool [0463] Pulse sequence: 600
cycles of: 5 seconds of precursor flow [0464] 3 seconds of nitrogen
purge [0465] 6 seconds of hydrogen plasma [0466] 3 seconds of
nitrogen purge
[0467] The film at point 5 on the saturation curve was
approximately 134 .ANG. thick.
[0468] At point 6 on the saturation curve the Beneq TFS 200 was
employed using capacitively coupled plasma and the following
conditions: [0469] Plasma: 170 W power with 140 sccm argon carrier
gas and 20 sccm hydrogen. [0470] Temperatures: 90.degree. C. source
temperature using a Beneq HS 500 hot source 225.degree. C. reactor
temperature. [0471] Carrier gases: 330 sccm nitrogen to the reactor
[0472] 220 sccm nitrogen to the tool [0473] Pulse sequence: 1600
cycles of: 6 seconds of precursor flow [0474] 3 seconds of nitrogen
purge [0475] 6 seconds of hydrogen plasma [0476] 3 seconds of
nitrogen purge
[0477] FIGS. 28 and 29 show micrographs of the approximately 350
.ANG. film produced at point 6. The image shown in FIG. 28 was
obtained using a Hitachi S-4800 field emission SEM (Accelerating
Voltage: 20000 Volt; Magnification: 120000.times.; Working
Distance: 15 mm). The image shown in FIG. 29 was obtained using a
Hitachi S-4800 field emission SEM (Accelerating Voltage: 20000
Volt; Magnification: 50000.times.; Working Distance: 15 mm).
[0478] The results of this study demonstrate the successful use of
an sNHC metal precursor in ALD. The compound tested was found to
perform better than, or equivalent to, two known precursors when
evaluated using the parameters listed in Table 2 below, where the
"best" values are indicated in bold. The data from the above study
are provided under the heading "Example 6".
TABLE-US-00002 TABLE 2 Comparison of ALD Parameters using sNHC
Metal Precursor and Previously Known Alternatives Parameters
Gordon.sup.1 Eisenbraun.sup.2 Example 6 ALD type thermal plasma
plasma mp (C.) 77 101 45 bubbler (C.) 100 100 90 process
(C.).sup..dagger. 150 100 225 stability (C.) 225 n/a >300 growth
rate, varying Cu (.ANG.) 0.1 0.2 0.21 plasma power (W) n/a 60 170
plasma time (s) n/a 16 6 .sup.1Li, Z.; Rahtu, A.; Gordon, R. G. J.
Electrochem. Soc. 2006, 153, C787. .sup.2Mao, J.; Eisenbraun, E.;
Omarjee, V.; Lansalot, C.; Dussarrat, C. Mat. Res. Soc. Symp. Proc.
2010, 1195, B12-05. .sup..dagger.There isn't a "best" value in this
category.
Example 8
Copper Film Deposition at Ambient Temperature
[0479] Mono-metallic precursor compounds 13a and 14a have been
shown to successfully deposit copper films from a solution of
deuterated benzene. The deuterated benzene was previously dried by
treating with sodium metal and benzophenone, degassing by a cycle
of freeze-pump-thaw; and vacuum distilling in an air-free solvent
storage flask. The dried, deuterated benzene was handled only in a
dry, oxygen-free glovebox after distillation.
[0480] Samples of the precursor compounds 13a and 14a were prepared
for .sup.1H NMR analysis inside of the glovebox (under nitrogen
atmosphere, 99.99%). Each sample was dissolved in dried
C.sub.6D.sub.6 and transferred to an NMR tube. The NMR tube was
capped inside the glovebox and heavily wrapped in Parafilm
immediately after removing from the glovebox in order to avoid
exposure of the solution to air.
[0481] The solutions of the compounds were maintained as prepared
(capped, heavily wrapped in Parafilm) under ambient conditions for
7 days. After 7 days a copper-coloured film was observed deposited
on the wall of the NMR tubes. A small amount of precipitated green
solid was also observed in solution in each case (see, FIGS. 30A
and B).
[0482] These results indicated that precursor compounds 13a and 14a
were able to successfully deposit copper metal films on a
substrate.
Example 9
Metal Deposition on Silicon and TiN Substrates
[0483] 1,3-Diisopropyl-4,5-dihydro-imidazolin-2-ylidene copper (I)
hexamethyldisilazide (2a) was used to demonstrate successful copper
film deposition to form composite materials comprising two
different substrate materials.
[0484] In this example, copper films were deposited by ALD using,
as the ALD tool, a Picosun SUNALE.TM. R200 employing an inductively
coupled plasma source. The metal depositions were performed as
described above (Example 6), at three reactor temperatures, under
the following conditions: [0485] Plasma: 1600 W power, 100 sccm,
90% argon, 10% hydrogen [0486] Temperatures: 140.degree. C. source
temperature using a Picosun Picosolid booster; [0487] 150.degree.
C., 180.degree. C., and 225.degree. C. reactor temperature [0488]
Pulse sequence: 1000 cycles of: 2 seconds of precursor flow [0489]
5 seconds of nitrogen purge [0490] 10 seconds of hydrogen plasma
[0491] 5 seconds of nitrogen purge
[0492] Film thickness was determined and modelled as described
above in Example 6. Growth rate was calculated by dividing the
thickness by the number of cycles. The results are provided in
Table 3, below:
TABLE-US-00003 TABLE 3 ALD with Varying Reactor Temperatures
Reactor Temperature (.degree. C.) Substrate Thickness (.ANG.) GR
(.ANG./cycle) 225 Si 231 0.231 TiN 164 0.164 180 Si 79 0.079 TiN
107 0.107 150 Si 37 0.037 TiN 32 0.032
[0493] Each of the composite materials formed by the above metal
deposition process was subjected to a Scotch tape test, wherein a
strip of Scotch tape was adhered to the copper film and then
removed. The tape was then examined for evidence of copper film. No
peeling of the copper film was observed from any of the composite
materials. These results were indicative of good adhesion of the
copper films to both substrates.
[0494] The results of this study demonstrate the successful use of
an sNHC metal precursor in ALD copper metal deposition on an Si and
a TiN substrate, using three different reactor temperatures.
Example 10
Synthesis and Characterization of Acyclic Diaminocarbenes
[0495] Materials and Methods
[0496] All manipulations were performed in an MBraun Labmaster.TM.
130 Dry box under a nitrogen atmosphere or in nitrogen filled
Schlenk lines. NMR spectra were recorded on a 400 MHz Bruker AMX.
NMR spectra that were measured in CDCl.sub.3 were referenced
against TMS. NMR spectra measured in C.sub.6D.sub.6 were referenced
against residual protonated solvent. Diisopropylformamide,
dimethylformamide, dimethylcarbamyl chloride, and phosphoryl
chloride were purchased from Alfa Aesar (VWR, Mississauga, Ontario,
Canada). Copper(I) chloride, sodium tert-butoxide, diisopropylamine
and hexamethyldisilazane were purchased from Sigma Aldrich Inc.
(Oakville, Ontario, Canada). The diethyl ether adduct of lithium
hexamethyldisilazide was prepared according to Lappert et al. JACS
1983, 105, 302.
[0497] Diethyl ether and toluene were purchased from Caledon
Laboratories Ltd. (Georgetown, Ontario, Canada) as reagent grade
and were purified from an MBraun Solvent Purifier System and stored
over 3 A molecular sieves. Anhydrous tetrahydrofuran, anhydrous
pentane and anhydrous dichloromethane were purchased from Sigma
Aldrich Inc. (Oakville, Ontario, Canada) and used as received.
[0498] N,N,N',N'-tetramethylformamidinium chloride was prepared
according to Wasserman, H. H., Ives, J. L. J. Org. Chem. 1985,
50(19), 3573-3579.
[0499] N,N,N',N'-tetraisopropylformamidinium chloride was prepared
according to Alder, R. W.; Allen, P. R.; Murray, M.; Orpen, A. G.
Angew. Chem. Int. Ed. Engl. 1996, 35(10), 1121-1123
Synthesis of N,N,N',N'-tetra isopropyl formamidinylidene copper(I)
hexamethyldisilazide 19a
##STR00026##
[0500] N,N,N',N'-tetraisopropylformamidinylidene copper(I)
hexamethyldisilazide 19a
[0501] N,N,N',N'-Tetraisopropylformamidinium chloride (0.569 g,
2.29 mmol) was suspended in 30 ml of tetrahydrofuran and copper(I)
chloride (0.233 g, 2.35 mmol) was added to the suspension. The
suspension was stirred for 18 h. A light pink solid was collected
by filtration, washed with 3.times.2 mL of tetrahydrofuran and then
dried under vacuum. (This solid was presumed to be of equal ratio
of the formamidinium chloride and copper(I) chloride). The solid
was treated with 2 molar equivalents of the diethyl ether adduct of
lithium hexamethyldisilazide. The pink solid (0.645 g, 1.85 mmol)
was suspended in 30 ml of toluene and cooled to -35.degree. C. The
diethyl ether adduct of lithium hexamethyldisilazide (0.895 g, 3.71
mmol) was dissolved in 10 ml of toluene and 10 ml of diethyl ether
and added dropwise. The resultant mixture was allowed to warm to
room temperature and was stirred for 18 h. The cloudy solution was
filtered and the insoluble fraction was washed with 2.times.2 ml of
toluene. The clear filtrate was combined with the washings and
concentrated under vacuum to 15 ml. The solution was chilled to
-35.degree. C. for 4 days to allow for the crystallization of a
colourless solid. The solid was collected by decanting the solution
and was dried under vacuum (0.598 g, 59.9%). .sup.1H NMR
(C.sub.6D.sub.6): .delta. 3.28 (4H, sept), .delta. 1.20 (24H, d),
.delta. 0.54 (s, 18H). .sup.13C NMR (C.sub.6D.sub.6): .delta.
220.95, .delta. 51.68, .delta. 24.04, .delta. 6.83.
[0502] An X-ray structure of compound 19a was obtained. The
crystals of 19a were mounted on thin glass fibers using paraffin
oil and the sample was cooled to 200.degree. K. prior to data
collection. Data were collected on a Bruker AXS SMART single
crystal diffractometer equipped with a sealed Mo tube source
(wavelength 0.71073 .ANG.) APEX II CCD detector. Raw data
collection and processing were performed with APEX II software
package from BRUKER AXS (APEX Software Suite v.2010, Bruker AXS:
Madison, Wis., 2005). Diffraction data for 19a sample were
collected with a sequence of 0.5.degree. .omega. scans at 0, 90,
180, and 270.degree. in .phi.. Initial unit cell parameters were
determined from 60 data frames collected at the different sections
of the Ewald sphere. Semi-empirical absorption corrections based on
equivalent reflections were applied (Blessing, R. Acta Cryst. 1995,
A51, 33).
[0503] Systematic absences in the diffraction data-set and
unit-cell parameters were consistent with triclinic C2/c (15) space
group. Solutions in centrosymmetric space group yielded chemically
reasonable and computationally stable results of refinement. The
structure was solved by direct methods, completed with difference
Fourier synthesis, and refined with full-matrix least-squares
procedures based on F.sup.2. In the structure, compound molecules
were located on two fold symmetry operator. Molecular packing
demonstrated positional disorder of SiMe.sub.3 groups and
N(i-Pr).sub.2 moieties. For the positions of SiMe.sub.3 units,
disorder was successfully modeled and computationally stable with
the ratio of 50%:50%. However, for the bis-amino part of the
structure disorder ration was refining to 55%:45%. All non-hydrogen
atoms were refined anisotropically with satisfactory thermal
parameter values. Positions of all hydrogen atoms were obtained
from the Fourier map analysis. After initial positioning all
hydrogen atoms were treated as idealized contributions. All
scattering factors were contained in several versions of the
SHELXTL program library, with the latest version used being v.6.12
(Sheldrick, G. M. Acta Cryst. 2008, A64, 112). Crystallographic
data and selected data collection parameters are reported in Table
4a below.
TABLE-US-00004 TABLE 4a Crystallographic data and selected data
collection parameters. Compound 19a Empirical formula
CuC.sub.19H.sub.46N.sub.3Si.sub.2 Formula weight 436.31 Crystal
size, mm 0.27 .times. 0.20 .times. 0.14 Crystal system Monoclinic
Space group C2/c No15 Z 4 a, .ANG. 15.3322(5) b, .ANG. 12.6279(4)
c, .ANG. 14.4925(5) .alpha., .degree. 90 .beta., .degree.
107.7560(10) .gamma., .degree. 90 Volume, .ANG..sup.3 2672.28(15)
Calculated density, Mg/m.sup.3 1.084 Absorption coefficient,
mm.sup.-1 0.914 F(000) 952 .THETA. range for data collection,
.degree. 2.13 to 28.32 Limiting indices h = .+-.20, k = .+-.15, l =
.+-.19 Reflections collected/unique 208365/3282 R(int) 0.0188
Completeness to .THETA. = 28.32, % 98.4 Max. and min. transmission
0.8827 and 0.7904 Data/restraints/parameters 3282/116/214
Goodness-of-fit on F.sup.2 1.059 Final R indices [I >
2.sigma.(I)] R.sub.1 = 0.0223, wR.sub.2 = 0.0559 R indices (all
data) R.sub.1 = 0.0262, wR.sub.2 = 0.0582 Largest diff. peak/hole,
e .ANG..sup.-3 0.268 and -0.152
[0504] An ORTEP drawing of the X-ray crystal structure of compound
19a is depicted in FIG. 31A.
Synthesis I of N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide 17a
##STR00027##
[0505] N,N,N',N'-tetramethylformamidinylidene copper(I)
chloride
[0506] In 80 ml of tetrahydrofuran,
N,N,N',N'-tetramethylformamidinium chloride (3.018 g, 22.1 mmol)
was suspended and copper(I) chloride (2.255 g, 22.8 mmol) was
added. The resultant mixture stirred for 15 min. A solution of
sodium tert-butoxide (2.188 g, 22.8 mmol) was dissolved in 20 ml of
tetrahydrofuran and added dropwise. The resultant mixture was
stirred for 24 h. The product suspension was filtered through a pad
of Celite.TM. and the insoluble fraction was washed with 3.times.10
ml of tetrahydrofuran. The filtrate and washings were combined and
the volatiles were stripped under reduced pressure. The solid
residue was dissolved in 15 ml of CH.sub.2Cl.sub.2 and concentrated
under reduced pressure to 10 ml. The solution was chilled to
-35.degree. C. for 24 h. Light brown crystals were collected by
decanting the solution and drying under vacuum (1.731 g, 39.3%). 1H
NMR (CDC.sub.3): .delta. 3.24 (12H, s). .sup.13C NMR (CDCl.sub.3):
.delta. 211.13, .delta. 45.07.
N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide 17a
##STR00028##
[0507] N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide
[0508] N,N,N',N'-tetramethylformamidinylidene copper(I) chloride
(0.369 g, 1.85 mmol) was suspended in 30 mL of toluene and chilled
to -35.degree. C. The diethyl ether adduct of lithium
hexamethyldisilazide (0.447 g, 1.85 mmol) was dissolved in 10 ml of
toluene and 5 ml of diethyl ether and added dropwise. The resultant
mixture was allowed to warm to room temperature and was stirred for
24 h. The cloudy solution was filtered and the insoluble fraction
was washed with 2.times.2 ml of toluene. The clear filtrate was
combined with the washings and concentrated under vacuum to 1 ml. 6
ml of pentane was added and the solution was chilled to -35 for 2
h. Colourless needle crystals were collected by decanting the
solution and drying under vacuum (0.298 g, 49.7%). .sup.1H NMR
(C.sub.6D.sub.6): .delta. 2.43 (12H, s), .delta. 0.56 (18H, s).
.sup.13C NMR (C.sub.6D.sub.6): .delta. 214.14, .delta. 44.01,
.delta. 7.23.
Synthesis II of N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide 17a
[0509] This synthesis of compound 17a is similar to the Synthesis I
above, except that in this procedure the intermediate carbene
copper chloride was not isolated.
N,N,N',N'-tetramethylformamidinylidene copper(I)
hexamethyldisilazide
[0510] N,N,N',N'-tetramethylformamidinium chloride (4.21 g, 30.8
mmol) was suspended in 100 mL of tetrahydrofuran. Copper(I)
chloride (3.15 g, 31.8 mmol) was added to the suspension. The
diethyl ether adduct of lithium hexamethyldisilazide (14.90 g, 61.7
mmol) was dissolved in 60 ml of tetrahydrofuran and added dropwise
to the suspension. The resultant mixture was stirred for 15 h.
Volatiles were stripped under reduced pressure. The residue was
extracted with 30 ml of pentane and then filtered through a medium
porosity frit. The insoluble fraction was washed with 3.times.10 ml
of pentane. The filtrate and washings were combined and the
solution was stripped to dryness under reduced pressure. The solid
residue was sublimed (20 mtorr, 90.degree. C.) to afford a product
yield of 8.746 g, 87.5%. .sup.1H NMR (C.sub.6D.sub.6): .delta. 2.43
(12H, s), .delta. 0.56 (18H, s). .sup.13C NMR (C.sub.6D.sub.6):
.delta. 214.14, .delta. 44.01, .delta. 7.23.
[0511] An X-ray structure of compound 17a was obtained. A crystal
of compound 17a was mounted on thin glass fibers using paraffin oil
and the sample was cooled to 200.degree. K prior to data
collection. Data were collected on a Bruker AXS SMART single
crystal diffractometer equipped with a sealed Mo tube source
(wavelength 0.71073 .ANG.) APEX II CCD detector. Raw data
collection and processing were performed with APEX II software
package from BRUKER AXS (APEX Software Suite v.2010; Bruker AXS:
Madison, Wis., 2005.). Diffraction data for the compound 17a sample
were collected with a sequence of 0.5.degree. .omega. scans at 0,
90, 180, and 270.degree. in .phi.. Initial unit cell parameters
were determined from 36 data frames collected at the different
sections of the Ewald sphere. Semi-empirical absorption corrections
based on equivalent reflections were applied (Blessing, R. Acta
Cryst. 1995, A51, 33). Systematic absences in the diffraction
data-set and unit-cell parameters were consistent with triclinic
P-1 (2) space group. Solutions in centrosymmetric space group
yielded chemically reasonable and computationally stable results of
refinement. The structure was solved by direct methods, completed
with difference Fourier synthesis, and refined with full-matrix
least-squares procedures based on F.sup.2. In the structure
compound molecules are situated in the general position. All
non-hydrogen atoms were refined anisotropically with satisfactory
thermal parameters values. Positions of all hydrogen atoms were
obtained from the Fourier map analysis. After initial positioning
all hydrogen atoms were treated as idealized contributions. All
scattering factors are contained in several versions of the SHELXTL
program library, with the latest version used being v.6.12
(Sheldrick, G. M. Cell_Now, 2004, Bruker-AXS, Inc., Madison, Wis.).
Crystallographic data and selected data collection parameters are
reported in Table 4b below.
TABLE-US-00005 TABLE 4b Crystallographic data and selected data
collection parameters. Compound 17a Empirical formula
CuC.sub.11H.sub.30N.sub.3Si.sub.2 Formula weight 324.10 Crystal
size, mm 0.19 .times. 0.17 .times. 0.13 Crystal system Triclinic
Space group P-1 No2 Z 2 a, .ANG. 8.6287(5) b, .ANG. 9.6320(5) c,
.ANG. 11.7862(6) .alpha., .degree. 80.207(2) .beta., .degree.
82.472(2) .gamma., .degree. 67.289(2) Volume, .ANG..sup.3 888.15(8)
Calculated density, Mg/m.sup.3 1.212 Absorption coefficient,
mm.sup.-1 1.352 F(000) 348 .THETA. range for data collection,
.degree. 2.31 to 28.30 Limiting indices h = .+-.10, k = .+-.11, l =
.+-.15 Reflections collected/unique 8286/4305 R(int) 0.0131
Completeness to .THETA. = 28.34, % 97.2 Max. and min. transmission
0.8438 and 0.7832 Data/restraints/parameters 4305/0/154
Goodness-of-fit on F.sup.2 1.042 Final R indices [I >
2.sigma.(I)] R.sub.1 = 0.0232, wR.sub.2 = 0.0642 R indices (all
data) R.sub.1 = 0.0265, wR.sub.2 = 0.0664 Largest diff. peak/hole,
e .ANG..sup.-3 0.354 and -0.266
[0512] An ORTEP drawing of the X-ray crystal structure of compound
17a is depicted in FIG. 31B.
Example 11
Thermogravimetric Analysis of Compounds Containing Acyclic
Diaminocarbenes
[0513] Vapour pressures of a two acyclic diaminocarbene-containing
copper precursor compounds were measured on a TA Instruments Q50
thermogravimetric (TG) analyser located in an MBraun Labmaster 130
Dry box under a nitrogen atmosphere. The TG analyzer was run in a
stepped isotherm as set out below.
[0514] Ramp program for N,N,N',N'-tetramethylformamidinylidene
copper(I) hexamethyldisilazide 17a:
[0515] 1: Ramp 40.00.degree. C./min to 110.00.degree. C.
[0516] 2: Isothermal for 15.00 min
[0517] 3: Ramp 40.00.degree. C./min to 120.00.degree. C.
[0518] 4: Isothermal for 15.00 min
[0519] 5: Ramp 40.00.degree. C./min to 130.00.degree. C.
[0520] 6: Isothermal for 15.00 min
[0521] 7: Ramp 40.00.degree. C./min to 140.00.degree. C.
[0522] 8: Isothermal for 15.00 min
[0523] 9: Ramp 40.00.degree. C./min to 150.00.degree. C.
[0524] 10: Isothermal for 15.00 min
[0525] 11: Ramp 40.00.degree. C./min to 160.00.degree. C.
[0526] 12: Isothermal for 15.00 min
[0527] 13: Ramp 40.00.degree. C./min to 170.00.degree. C.
[0528] 14: Isothermal for 15.00 min
[0529] 15: Ramp 40.00.degree. C./min to 180.00.degree. C.
[0530] 16: Isothermal for 120.00 min
[0531] 17: Ramp 40.00.degree. C./min to 600.00.degree. C.
[0532] Ramp program for N,N,N',N'-tetra isopropyl formamidinylidene
copper(I) hexamethyldisilazide 19a:
[0533] 1: Ramp 40.00.degree. C./min to 110.00.degree. C.
[0534] 2: Isothermal for 15.00 min
[0535] 3: Ramp 40.00.degree. C./min to 120.00.degree. C.
[0536] 4: Isothermal for 10.00 min
[0537] 5: Ramp 40.00.degree. C./min to 130.00.degree. C.
[0538] 6: Isothermal for 10.00 min
[0539] 7: Ramp 40.00.degree. C./min to 140.00.degree. C.
[0540] 8: Isothermal for 10.00 min
[0541] 9: Ramp 40.00.degree. C./min to 150.00.degree. C.
[0542] 10: Isothermal for 10.00 min
[0543] 11: Ramp 40.00.degree. C./min to 160.00.degree. C.
[0544] 12: Isothermal for 10.00 min
[0545] 13: Ramp 40.00.degree. C./min to 170.00.degree. C.
[0546] 14: Isothermal for 10.00 min
[0547] 15: Ramp 40.00.degree. C./min to 180.00.degree. C.
[0548] 16: Isothermal for 10.00 min
[0549] 17: Ramp 40.00.degree. C./min to 190.00.degree. C.
[0550] 18: Isothermal for 10.00 min
[0551] 19: Ramp 40.00.degree. C./min to 200.00.degree. C.
[0552] 20: Isothermal for 10.00 min
[0553] 21: Ramp 10.00.degree. C./min to 600.00.degree. C.
[0554] As in Example 5, the slope was determined for each isotherm
interval, and if the data was linear for that interval, that was
used as the ".DELTA.m/.DELTA.t" value for that temperature. The
pressure was calculated using the Langmuir equation following the
method of Umarji [G. V. Kunte, S. A. Shivashanker, A. M. Umarji
Meas. Sci. Tech. 2008, 19, 025704] for estimation of vapour
pressure. Benzoic acid was used as a standard to determine the
.alpha. coefficient of the Langmuir equation (i.e., the Langmuir
adsorption constant), and Cu(tmhd).sub.2 was used as a
benchmark.
[0555] The results from vapour testing of the two acyclic
diaminocarbene-containing copper precursor compounds are depicted
in FIG. 32. The compound, Cu(tmhd).sub.2, was used as a control.
The temperatures at which compounds 17a and 19a have a vapour
pressure of 1 torr were 126.degree. C. and 157.degree. C.,
respectively.
[0556] Further TG analysis was performed on the TA Instruments Q50
thermogravimetric (TG) analyser located in an MBraun Labmaster 130
Dry box under a nitrogen atmosphere (99.9990/% at a flow rate of
100 mL/min) to obtain weight loss curves. During testing the
furnace was heated at 10.degree. C./min from 30 to 600.degree. C.
Samples of the compounds to be studied were provided in platinum
pans with diameters of 1 cm. The mass of each sample tested was
within the range of from about 10 to about 30 mg. The mass
("weight") of the sample was obtained as the temperature was
increased and plotted.
[0557] The results are provided in FIGS. 33 and 34. The residual
mass (% mass that remains in the platinum pan after 600.degree. C.)
is displayed in bottom right corner of each graph. These results
demonstrated that the acyclic diaminocarbene-containing copper
precursors tested had good volatility and thermal stability. The
residual masses of less than 5% was indicative of good volatility
and negligible decomposition.
Example 12
Synthesis and Characterization of Silver and Gold sNHC
Precursors
[0558] Materials and Methods
[0559] All manipulations were performed in an MBraun Labmaster.TM.
130 Dry box under a nitrogen atmosphere or in nitrogen filled
Schlenk lines. All reaction vessels were wrapped in aluminum foil
to exclude light. NMR spectra were recorded on a 400 MHz Bruker
AMX. NMR spectra that were measured in CDCl.sub.3 were referenced
against TMS. NMR spectra measured in C.sub.6D.sub.6 were referenced
against residual protonated solvent. Hydrogen tetrachloroaurate
(III) hydrate and silver(I) chloride were purchased from Strem
Chemicals (NewburyPort, Mass., USA). Tetrahydrothiophene and
hexamethyldisilazane were purchased from Sigma Aldrich Inc.
(Oakville, Ontario, Canada). The diethyl ether adduct of lithium
hexamethyldisilazide was prepared according to Lappert et al. JACS
1983, 105, 302.
[0560] Diethyl ether, and toluene were purchased from Caledon
Laboratories Ltd. (Georgetown, Ontario, Canada) as reagent grade
and were purified from an MBraun Solvent Purifier System and stored
over 3 A molecular sieves. Anhydrous tetrahydrofuran, anhydrous
pentane and anhydrous dichloromethane were purchased from Sigma
Aldrich Inc. (Oakville, Ontario, Canada) and used as received.
Tetrahydrothiophene gold(I) chloride
##STR00029##
[0562] Au(THT)Cl (THT=tetrahydrothiophene) was prepared according
to a literature procedure with small modifications (Melgarejo, D.
Y.; Chiarella, G. M.; Fackler, J. P. Jr.; Perez, L. M.;
Rodrigue-Witchel, A.; Reber, C. Inorg. Chem. 2011, 4238-4240).
[0563] Hydrogen tetrachloroaurate (III) hydrate (8.22 g, 49% Au,
20.45 mmol of Au) was dissolved in 20 mL of water and 100 mL of
ethanol (approx. a 1:5 mixture) in a 400 mL beaker. The colour of
the solution was orange. Tetrahydrothiophene (4.2 mL, 47.64 mmol)
was added dropwise while the solution was stirred. A deep red
colour occurred with each drop of THT, but quickly dissipated. A
colourless precipitate gradually formed and the solution cleared to
a pale yellow. The suspension was stirred for 1 hour. The white
solid was filtered off and washed 3 times with 20 mL of ethanol and
then 3 times with 20 mL of diethyl ether. The solid was dried under
high vacuum overnight to obtain 6.36 g, 97.1%.
1,3-diisopropyl-imidazolidin-2-ylidene gold(I) chloride and
1,3-diisopropyl-imidazolidin-2-ylidene silver(I) chloride
##STR00030##
[0564] 1,3-Diisopropyl-imidazolidin-2-ylidene gold(I) chloride
[0565] 1,3-Diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride
(1.654 g, 8.08 mmol) was suspended in 100 mL of THF to which a
solution of the diethyl ether adduct of lithium
hexamethyldisilazide (1.951 g, 8.08 mmol) in 80 mL of Et.sub.2O was
added dropwise. The suspension was stirred for 1 hour during which
a clear solution formed. This solution was then cooled in a dry
ice/acetone bath to -78.degree. C. and Au(THT)Cl (2.590 g, 8.08
mmol), was added as a solid in 5 portions five minutes apart.
Stirring proceeded for 4 h at -78.degree. C. The cooling bath was
then removed and the reaction was warmed in an ice water bath.
Volatiles were then stripped under high vacuum at 0.degree. C. When
the solid residue appeared dry, the reaction vessel was allowed to
warm to r.t and drying under vacuum continued for 1 h. The solid
was extracted 3 times with 20 mL of CH.sub.2Cl.sub.2. The combined
CH.sub.2Cl.sub.2 extractions were filtered and volatiles were
stripped under vacuum. The solid residue was washed with pentane
until the washings were colourless. 3.03 g, 97.0%, of an off white
solid was obtained. .sup.1H NMR (CDCl.sub.3): .delta. 4.76 (sept,
2H), .delta. 3.54 (s, 4H), .delta. 1.23 (d, 12H) .sup.13C NMR
(CDCl3): .delta. 190.41, .delta. 81.82, .delta. 42.23, .delta.
20.52.
1,3-Diisopropyl-imidazolidin-2-ylidene silver(I) chloride
[0566] 1,3-Diisopropyl-4,5-dihydro-3H-imidazol-1-ium chloride
(0.266 g, 1.39 mmol) was suspended in 10 ml of THF. A solution of
the diethyl ether adduct of lithium hexamethyldisilazide (0.333 g,
1.38 mmol) dissolved in 20 ml of toluene was added and the mixture
was stirred for 1 h. The solution was cooled in a dry ice/acetone
bath to -78.degree. C. and silver(I) chloride (0.180 g, 1.26 mmol)
was added. Stirring proceeded for 2.5 h as the solution gradually
warmed from -78.degree. C. to 0.degree. C. Volatiles were stripped
under reduced pressure to afford a pale yellow solid. The solid was
extracted with 15 ml of CH.sub.2Cl.sub.2 and then filtered. The
filtrate was concentrated to 4 ml and 15 ml of Et.sub.2O was added.
The solution was kept at -35.degree. C. for 24 h. Colourless
needles were collected by decanting the solution and drying the
crystals under vacuum; obtained 0.282 g, 78%. .sup.1H NMR
(CDCl.sub.3): .delta. 4.32 (sept, 2H), .delta. 3.55 (s, 4H),
.delta. 1.22 (d, 12H) .sup.13C (CDCl.sub.3): .delta. 52.52, .delta.
42.69, .delta. 21.00, carbenic carbon not observed.
Synthesis of 1,3-diisopropyl-imidazolidin-2-ylidene gold(I)
hexamethyldisilazide 2c and 1,3-diisopropyl-imidazolidin-2-ylidene
silver(I) 2b hexamethyldisilazide
##STR00031##
[0567] 1,3-Diisopropyl-imidazolidin-2-ylidene gold(I)
hexamethyldisilazide, 2c
[0568] 1,3-diisopropyl-imidazolidin-2-ylidene gold(I) chloride
(3.01 g, 7.79 mmol) was suspended in 150 mL of toluene and cooled
to -35.degree. C. in a freezer. The suspension was removed from the
freezer and a solution of the diethyl ether adduct of lithium
hexamethyldisilazide (1.951 g 8.08 mmol) in 70 mL of toluene was
added dropwise. The reaction vessel was allowed to warm to room
temperature and stirring was continued for 18 h. The obtained
cloudy solution was filtered and volatiles were stripped from the
filtrate under high vacuum. The crude solid was sublimed at
90.degree. C. at 40 mtorr employing a -78.degree. C. cold finger.
3.55 g, 89.1%, of a pale yellow solid was obtained. .sup.1H NMR
(C.sub.6D.sub.6): .delta. 4.81 (sept, 2H), .delta. 2.38 (s, 4H),
.delta. 0.77 (d, 12H), .delta. 0.62 (s, 18H). .sup.13C NMR
(C.sub.6D.sub.6): .delta. 197.68, .delta. 50.70, .delta. 41.55,
.delta. 20.04, .delta. 6.90.
1,3-Diisopropyl-imidazolidin-2-ylidene silver(I)
hexamethyldisilazide, 2b
[0569] 1,3-Diisopropyl-imidazolidin-2-ylidene silver(I) chloride
(0.278 g, 0.99 mmol) was stirred in 20 ml of a 1:1 mixture of
toluene to THF and cooled to -35.degree. C. in a freezer. The
solution was removed from the freezer and a solution of the diethyl
ether adduct of lithium hexamethyldisilazide (0.226 g, 0.94 mmol)
dissolved in 10 ml of Et.sub.2O was added dropwise. The solution
was allowed to warm to room temperature and stirring was continued
for 18 h. Volatiles were stripped under reduced pressure and the
residue was stirred with 10 ml of pentane and then filtered. The
pentane solution was concentrated to 2 ml under vacuum and kept in
a -35.degree. C. freezer for several days. Colourless needle
crystals (0.261 g, 66%) were collected by decanting the solution
and drying the crystals under vacuum. .sup.1H NMR (C.sub.6D.sub.6):
.delta. 4.25 (sept, 2H), .delta. 2.43 (s, 4H), .delta. 0.72 (d,
12H), .delta. 0.61 (s, 18H). .sup.13C NMR (C.sub.6D.sub.6): .delta.
204.80, .delta. 204.66, .delta. 202.88, .delta. 202.75, .delta.
51.80, .delta. 42.00, .delta. 41.94, .delta. 20.52, .delta.
7.42.
Example 13
Thermogravimetric Analysis of Silver and Gold Precursor
Compounds
[0570] Vapour pressures of a silver and a gold precursor compound
were measured on a TA Instruments Q50 thermogravimetric (TG)
analyser located in an MBraun Labmaster 130 Dry box under a
nitrogen atmosphere. The TG analyzer was run in a stepped isotherm
as set out below, using lower temperatures than used in the
Examples above in order to minimize the amount of decomposition of
the silver and gold precursor compounds.
[0571] Ramp program for 1,3-diisopropyl-imidazolidin-2-ylidene
gold(I) hexamethyldisilazide 2c:
[0572] 1: Ramp 40.00.degree. C./min to 80.00.degree. C.
[0573] 2: Isothermal for 20.00 min
[0574] 3: Ramp 40.00.degree. C./min to 90.00.degree. C.
[0575] 4: Isothermal for 15.00 min
[0576] 5: Ramp 40.00.degree. C./min to 100.00.degree. C.
[0577] 6: Isothermal for 15.00 min
[0578] 7: Ramp 40.00.degree. C./min to 110.00.degree. C.
[0579] 8: Isothermal for 15.00 min
[0580] 9: Ramp 40.00.degree. C./min to 120.00.degree. C.
[0581] 10: Isothermal for 15.00 min
[0582] 11: Ramp 40.00.degree. C./min to 130.00.degree. C.
[0583] 12: Isothermal for 15.00 min
[0584] 13: Ramp 40.00.degree. C./min to 140.00.degree. C.
[0585] 14: Isothermal for 15.00 min
[0586] 15: Ramp 40.00.degree. C./min to 150.00.degree. C.
[0587] 16: Isothermal for 15.00 min
[0588] 17: Ramp 40.00.degree. C./min to 160.00.degree. C.
[0589] 18: Isothermal for 240.00 min
[0590] 19: Ramp 40.00.degree. C./min to 600.00.degree. C.
[0591] Ramp program for 1,3-diisopropyl-imidazolidin-2-ylidene
silver(I) hexamethyldisilazide 2b:
[0592] 1: Ramp 40.00.degree. C./min to 70.00.degree. C.
[0593] 2: Isothermal for 40.00 min
[0594] 3: Ramp 40.00.degree. C./min to 80.00.degree. C.
[0595] 4: Isothermal for 20.00 min
[0596] 5: Ramp 40.00.degree. C./min to 90.00.degree. C.
[0597] 6: Isothermal for 20.00 min
[0598] 7: Ramp 40.00.degree. C./min to 100.00.degree. C.
[0599] 8: Isothermal for 20.00 min
[0600] 9: Ramp 40.00.degree. C./min to 110.00.degree. C.
[0601] 10: Isothermal for 20.00 min
[0602] 11: Ramp 40.00.degree. C./min to 120.00.degree. C.
[0603] 12: Isothermal for 20.00 min
[0604] 13: Ramp 40.00.degree. C./min to 130.00.degree. C.
[0605] 14: Isothermal for 20.00 min
[0606] 15: Ramp 40.00.degree. C./min to 140.00.degree. C.
[0607] 16: Isothermal for 20.00 min
[0608] 17: Ramp 40.00.degree. C./min to 150.00.degree. C.
[0609] 18: Isothermal for 20.00 min
[0610] 19: Ramp 10.00.degree. C./min to 600.00.degree. C.
[0611] As in Example 5, the slope was determined for each isotherm
interval, and if the data was linear for that interval, that was
used as the ".DELTA.m/.DELTA.t" value for that temperature. The
pressure was calculated using the Langmuir equation following the
method of Umarji [G. V. Kunte, S. A. Shivashanker, A. M. Umarji
Meas. Sci. Tech. 2008, 19, 025704] for estimation of vapour
pressure. Benzoic acid was used as a standard to determine the
.alpha. coefficient of the Langmuir equation (i.e., the Langmuir
adsorption constant), and Cu(tmhd).sub.2 was used as a
benchmark.
[0612] The results from vapour testing of the sNHC-containing
silver and gold precursor compounds are depicted in FIG. 35. The
compound, Cu(tmhd).sub.2, was used as a control. The temperature at
which both compounds 2b and 2c have a vapour pressure of 1 torr was
142.degree. C.
Example 14
ALD of Gold Using a Gold Precursor Compound
[0613] 1,3-Diisopropyl-4,5-dihydro-imidazolin-2-ylidene gold (I)
hexamethyldisilazide (2c) was used to demonstrate successful gold
film deposition to form composite materials from two substrate
materials.
[0614] In this example, gold films were deposited by ALD using, as
the ALD tool, a Picosun SUNALE.TM. R200 employing an inductively
coupled plasma source. A small amount of precursor (0.3-0.5 g) was
loaded into a bubbler and attached to the ALD tool. A mixture of
10% H.sub.2 in Ar (balance) was used as the plasma source. A 200 mm
silicon substrate with a previously-deposited ruthenium film was
introduced to the deposition chamber. The plasma used was a
capacitively coupled plasma using screens to prevent ions from
reaching the substrate. The conditions used for ALD were as
follows: [0615] Plasma: 2500 W power, 20 sccm, 90% argon, 10%
hydrogen [0616] Temperatures: 100.degree. C. source temperature
using a Picosun Picosolid.TM. booster with 80 sccm of nitrogen;
[0617] 200.degree. C. reactor temperature [0618] Pulse sequence:
2000 cycles of: [0619] 3 seconds of precursor flow [0620] 5 seconds
of nitrogen purge [0621] 10 seconds of hydrogen plasma [0622] 4
seconds of nitrogen purge
[0623] Under the above conditions, gold was successfully deposited
by ALD to form a thin gold film on the ruthenium-silicon
substrate.
Example 15
Thermal Stress Study of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a)
[0624] A 0.8 g sample of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) was loaded into a stainless steel vessel,
which was inlet capped with a VCR.RTM. gasket. The vessel was then
heated in an oven at 92.degree. C. and maintained in the oven for
two weeks. Every two days, a sample of the compound was removed and
tested. In order to obtain a sample for testing, the vessel was
removed from the oven and cooled to room temperature in a glovebox.
Following removal of the sample, the vessel was returned to the
92.degree. C. oven.
[0625] Approximately twenty milligrams of each two-day sample was
tested by thermogravimetric analysis. In each case, the
approximately 20 mg sample was loaded onto a 1 cm platinum pan and
heated at a heating rate of 10.degree. C./min up to 500.degree. C.
In addition, 5-10 mg of the initial sample (i.e., prior to heating)
and the final sample (i.e., tested on day 15 of heating) were
tested using .sup.1H NMR.
[0626] The results of the thermogravimetric analysis are shown in
FIG. 36 and summarized in Table 5 below.
TABLE-US-00006 TABLE 5 Thermal Stress results Time (h) Sample Mass
(mg) Residual Mass (%) 0 20.97 2.11 24 20.44 3.03 72 27.00 3.45 120
21.59 1.69 168 21.13 2.11 216 20.33 2.01 264 21.52 2.23 312 20.49
2.57 360 20.26 2.96
[0627] These results showed that the residual mass varied between
2-3.5%, with no clear increase in residual mass observed from the
compound following heating for two weeks.
[0628] FIG. 37 shows the .sup.1H NMR spectrum of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) prior to heating. FIG. 38 shows the
.sup.1H NMR spectrum of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) after heating at 92.degree. C. for 360
hours (15 days). The spectrum from the sample following heating for
15 days was identical to the starting spectrum. The minor peaks in
the spectra were from impurities present in the initial sample
(they are visible in both spectra).
[0629] The results of the thermogravimetric analysis and the
.sup.1H NMR studies demonstrated that there was no detectable
decomposition of
(1,3-diisopropyl-4,5-dihydro-1H-imidazolin-2-ylidene) copper
hexamethyldisilazide (2a) following heating at 92.degree. C. for
two weeks.
[0630] All publications, patents and patent applications mentioned
in this Specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
[0631] Modifications and improvements to the above-described
embodiments of the present invention may become apparent to those
skilled in the art. The foregoing description is intended to be
exemplary rather than limiting. The scope of the present invention
is therefore intended to be limited solely by the scope of the
appended claims.
* * * * *