U.S. patent application number 15/691893 was filed with the patent office on 2018-06-21 for leveling additives for electrodeposition.
This patent application is currently assigned to Xtalic Corporation. The applicant listed for this patent is Xtalic Corporation. Invention is credited to Joshua Garth Abbott, Evgeniya Freydina.
Application Number | 20180171498 15/691893 |
Document ID | / |
Family ID | 55454198 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180171498 |
Kind Code |
A1 |
Abbott; Joshua Garth ; et
al. |
June 21, 2018 |
LEVELING ADDITIVES FOR ELECTRODEPOSITION
Abstract
Leveling additives, their use in electrodeposition, and
regeneration are described. In one embodiment, an electrodeposition
bath may include a non-aqueous liquid and an optionally substituted
aromatic hydrocarbon. The optionally substituted aromatic
hydrocarbon may be protonated.
Inventors: |
Abbott; Joshua Garth;
(Marlborough, MA) ; Freydina; Evgeniya; (Acton,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xtalic Corporation |
Marlborough |
MA |
US |
|
|
Assignee: |
Xtalic Corporation
Marlborough
MA
|
Family ID: |
55454198 |
Appl. No.: |
15/691893 |
Filed: |
August 31, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14489107 |
Sep 17, 2014 |
9752242 |
|
|
15691893 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/56 20130101; C25D
3/44 20130101; C25C 3/06 20130101; C25D 21/18 20130101; C25D 21/14
20130101; C25D 3/665 20130101; C25D 5/18 20130101 |
International
Class: |
C25D 3/44 20060101
C25D003/44; C25D 5/18 20060101 C25D005/18; C25C 3/06 20060101
C25C003/06; C25D 3/56 20060101 C25D003/56; C25D 3/66 20060101
C25D003/66 |
Claims
1. An electrodeposition bath comprising: a non-aqueous liquid; and
an optionally substituted aromatic hydrocarbon.
2-5. (canceled)
6. The electrodeposition bath of claim 1, wherein the optionally
substituted aromatic hydrocarbon has a concentration in the
electrodeposition bath between or equal to about 0.5 weight percent
and 10 weight percent relative to the non-aqueous liquid.
7. The electrodeposition bath of claim 1, wherein the optionally
substituted aromatic hydrocarbon is a polymer.
8. The electrodeposition bath of claim 1, wherein a substituent of
the optionally substituted aromatic hydrocarbon includes at least
one of an alkyl, aryl, and polyalkoxy chain.
9. (canceled)
10. A method comprising: electrodepositing a material in an
electrodeposition bath, wherein the electrodeposition bath includes
a non-aqueous liquid and an optionally substituted aromatic
hydrocarbon.
11-45. (canceled)
46. An electrodeposition system comprising: an electrodeposition
bath including a non-aqueous liquid; and an optionally substituted
aromatic hydrocarbon; an anode at least partially immersed in the
electrodeposition bath; and a cathode at least partially immersed
in the electrodeposition bath.
47. (canceled)
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/489,107, filed Sep. 17, 2014, which is incorporated herein
by reference in its entirety.
FIELD
[0002] Disclosed embodiments are related to leveling additives for
electrodeposition.
BACKGROUND
[0003] In order to obtain smooth and dense metallic deposits during
electrodeposition, it is a common practice to utilize additives
that act as leveling additives. The additives are usually surface
active, and adsorb onto areas of the surface with the highest
charge density. This leads to the suppression of deposition at high
energy sites, while making deposition at lower energy sites more
favorable providing a more even deposition across the surface.
SUMMARY
[0004] In one embodiment, an electrodeposition bath may include a
non-aqueous liquid and an optionally substituted aromatic
hydrocarbon.
[0005] In another embodiment, a method may include:
electrodepositing a material in an electrodeposition bath including
a non-aqueous liquid and an optionally substituted aromatic
hydrocarbon.
[0006] In yet another embodiment, a method for preparing an
electrodeposition bath with a leveling additive may include: adding
an optionally substituted basic aromatic hydrocarbon to a
non-aqueous liquid; and protonating the basic aromatic hydrocarbon
in the non-aqueous liquid.
[0007] In another embodiment, a method may include: adding protons
to an electrodeposition bath including a non-aqueous liquid and an
optionally substituted basic aromatic hydrocarbon. The protons may
react with the optionally substituted basic aromatic hydrocarbon to
form an optionally substituted protonated aromatic hydrocarbon.
[0008] In yet another embodiment, a method for reducing the acidity
of an electrodeposition bath may include: adding an optionally
substituted basic aromatic hydrocarbon to a non-aqueous liquid,
wherein the optionally substituted basic aromatic hydrocarbon
reacts with one or more protons in the electrodeposition bath to
form an optionally substituted protonated aromatic hydrocarbon.
[0009] In another embodiment, an electrodeposition system may
include an electrodeposition bath with a non-aqueous liquid and an
optionally substituted protonated aromatic hydrocarbon. The
electrodeposition system may also include an anode at least
partially immersed in the electrodeposition bath and a cathode at
least partially immersed in the electrodeposition bath.
[0010] It should be appreciated that the foregoing concepts, and
additional concepts discussed below, may be arranged in any
suitable combination, as the present disclosure is not limited in
this respect. Further, other advantages and novel features of the
present disclosure will become apparent from the following detailed
description of various non-limiting embodiments when considered in
conjunction with the accompanying figures.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The accompanying drawings are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component that is illustrated in various figures may be represented
by a like numeral. For purposes of clarity, not every component may
be labeled in every drawing. In the drawings:
[0012] FIG. 1 is a schematic representation of an electrodeposition
system;
[0013] FIG. 2 is a schematic representation of anthracene
(C.sub.14H.sub.10) undergoing a reaction with a proton (H.sup.+) to
form protonated anthracene (C.sub.14H.sub.11).sup.+;
[0014] FIG. 3 is a schematic representation of protonated
anthracene (C.sub.14H.sub.11).sup.+ being reduced to form
anthracene (C.sub.14H.sub.10) and a proton (H.sup.+);
[0015] FIG. 4 is a graph of ultraviolet/visible absorption spectra
for increasing concentrations of protonated leveling additive in an
electrodeposition bath;
[0016] FIGS. 5A-5C depict electrodeposited an aluminum manganese
alloy on copper samples where the electrodeposition bath was
regenerated between electrodeposition cycles; and
[0017] FIG. 6 depicts electrodeposited an aluminum manganese alloy
on copper samples where the electrodeposition bath was regenerated
continuously during electrodeposition.
DETAILED DESCRIPTION
[0018] Many types of coatings may be applied on a base material.
Electrodeposition is a common technique for depositing such
coatings. Electrodeposition generally involves applying a voltage
to a base material placed in an electrodeposition bath to reduce
metal ionic species within the bath which deposit on the base
material in the form of a metal, or metal alloy, coating. The
voltage may be applied between an anode and a cathode using a power
supply. The anode or cathode may serve as the base material to be
coated. In some electrodeposition processes, the voltage may be
applied as a complex waveform such as in pulse deposition,
alternating current deposition, or reverse-pulse deposition.
[0019] Oftentimes leveling additives are used to obtain smooth
dense deposits during electrodeposition by suppressing the
formation of dendrites. Without wishing to be bound by theory,
leveling additives are usually surface active, and adsorb onto
areas of the surface with the highest charge density. While many
types of leveling additive functionalities may lead to this
behavior, in some instances a leveling additive including a
positively charged compound is attracted towards high energy sites
on the negatively charged cathode during electrodeposition. By
adsorbing onto the high energy sites, the leveling additives may
make electrodeposition at the lower energy sites more favorable
leading to a more even deposition across the surface.
[0020] The inventors have recognized that the lack of effective
surface leveling additives for non-aqueous liquids, including ionic
liquids, to suppress dendritic growth and enable the formation of
smooth dense deposits has hampered the development of high rate
deposition methods. Furthermore, given the differences between
these non-aqueous electrodeposition baths and previous aqueous
based electrodeposition baths, it is not clear that additives and
methods used for aqueous based electrolyte baths are capable of
working in ionic liquid based electrodeposition systems.
[0021] In view of the above, the inventors recognized the benefits
associated with aromatic hydrocarbons that are sufficiently basic
to be stable proton addition complexes capable of forming a stable
protonated species in a non-aqueous liquid and functioning as
leveling additives. This is in comparison to the use of aromatic
hydrocarbons in aqueous electrodeposition baths where the
protonated species are not stable and the non-protonated compounds
are only used as surfactants. In some embodiments, the aromatic
hydrocarbons described herein may be optionally substituted as
described in more detail below. For example, possible substituents
include, but are not limited to, alkyls, aryls, and polyalkoxy
chains. For the purposes of this application, aromatic hydrocarbons
should be understood to include polyaromatic hydrocarbons.
[0022] In some embodiments, an aromatic hydrocarbon capable of
being protonated in the non-aqueous electrodeposition bath may be a
polymer. Suitable polymers include, but are not limited to
polystyrenes.
[0023] In view of the above, in one embodiment, the inventors have
recognized the benefits associated with a leveling additive
including a protonated aromatic hydrocarbon used in an
electrodeposition bath including a non-aqueous liquid. Without
wishing to be bound by theory, the protonated additives are charged
cations that are attracted to the negatively charged cathode.
Therefore, the protonated additives form a surface active layer
which may suppress electrodeposition in regions of high current
density thus aiding in obtaining level deposits. During use, the
protonated additives may undergo a reduction reaction as described
in more detail below. After being reduced, the additives may no
longer function as leveling additives. Therefore, in some
embodiments, it may be desirable to regenerate the
electrodeposition bath by introducing protons, or a source of
protons such as an acid, to react with the leveling additives to
form the previously noted protonated aromatic hydrocarbons.
[0024] For the purposes of this application, the terms
"protonation", "protonated molecule", "reactions with protons", and
similar phrases refer to a molecule that has reacted with a proton
(H.sup.+) to form a positive cation. It should be understood, that
a proton may correspond to any positive hydrogen isotope including,
but not limited to, .sup.1H.sup.+, .sup.2H.sup.+, and
.sup.3H.sup.+.
[0025] It should be understood that the protonated aromatic
hydrocarbons may be provided in any number of ways. For example, in
one embodiment, a protonated aromatic hydrocarbon may be formed
prior to introduction into an electrodeposition bath.
Alternatively, in another embodiment, a basic aromatic hydrocarbon
may be added to an electrodeposition bath including a non-aqueous
liquid where it reacts with protons already in, or that may be
added to, the electrodeposition bath to form the protonated
compounds. Similarly, previously protonated additives that have
been reduced may be regenerated by reacting with protons either
already in, or that may be added to, an electrodeposition bath to
form the protonated compounds. Without wishing to be bound by
theory, it is not well understood whether or not the protons are
completely disassociated within the non-aqueous electrodeposition
bath. For example, in a chloroaluminate ionic liquid the chloride
cation may be partially bound to both an aluminum anion and/or a
proton from a partially disassociated acid such as HCl. However, in
either case, once a sufficiently basic aromatic hydrocarbon is
introduced, it may react with the proton to become a protonated
aromatic hydrocarbon.
[0026] Without wishing to be bound by theory, a measure of the
basicity of an aromatic hydrocarbon may be given by the basicity
constant, K, more generally given as log(K). The range of log(K)
for aromatic hydrocarbons typically varies from -9.4 to 6.5. A more
negative value of log(K) is less basic, and a more positive value
of log(K) is more basic. Aromatic hydrocarbons with strong negative
values are thus more difficult to protonate. However, compounds
with large positive log(K) values may be too reactive for use as a
leveling additive. Therefore, in some embodiments the log(K) value
of an aromatic hydrocarbon for use as a leveling additive in a
non-aqueous electrodeposition bath may be between or equal to -3 to
5, -1 to 3, or any other appropriate range both greater than and
less than those noted above.
[0027] In embodiments where it is desirable to add protons to an
electrodeposition bath to either initially prepare or regenerate a
leveling additive, the protons may be added in any number of ways.
In one embodiment, an acid may be added to the electrodeposition
bath to provide the protons. The acid may be added to the
electrodeposition bath by bubbling a dry gaseous acid through the
electrodeposition bath, adding a more acidic non-aqueous liquid to
the electrodeposition bath, and/or any other appropriate method. In
such an embodiment, the acid may be a strong acid such as hydrogen
chloride, hydrogen bromide, hydrogen iodide, and other appropriate
acids that disassociate to form acidic protons in the
electrodeposition bath.
[0028] In another embodiment, materials may be added to an
electrodeposition bath that react with the electrodeposition bath
to form an acid to provide the desired protons. For example,
compounds including hydroxyl (--OH) groups may be added to the
electrodeposition bath to form an acid. In one embodiment, water
and/or hydrates, such as aluminum chloride hydrate, may be added to
the electrodeposition bath. In some embodiments, the hydrate may
include elements that are already present within the
electrodeposition bath. In another embodiment, alumina, silica,
and/or other materials including surface hydroxyl groups capable of
reacting with the electrodeposition bath to form an acid, and that
are compatible with an electrodeposition process, may be added to
an electrodeposition bath to form an acid and provide the desired
protons. The materials including surface hydroxyl groups may be
provided in any desirable form including, but not limited to,
particles, flakes, foams, and/or any other appropriate form.
Without wishing to be bound by theory, the surface area to volume
ratio increases with decreasing particle size. Therefore, smaller
size scale materials may exhibit more surface hydroxyl groups
relative to their volume than larger size scale materials. While
any appropriate size material may be used, in some embodiments, a
material including surface hydroxyl groups may have a size that is
between or equal to about 10 .mu.m and 200 .mu.m, though sizes both
less than and greater than that noted above are contemplated. In
yet another embodiment, compounds including hydroxyl groups, such
as cellulose, may be added to the electrodeposition bath to undergo
a reaction to form the desired acid. Again, compounds including a
hydroxyl group may be provided in any form and size including
particles, foams, and/or flakes.
[0029] Depending on the electrodeposition process, protons may be
added to the electrodeposition bath either continuously, or in
batches, as the disclosure is not so limited. For example, a dry
gaseous acid may be bubbled continuously through the
electrodeposition bath at a predetermined rate, or the dry gaseous
acid may be bubbled through the electrodeposition bath at
predetermined intervals to maintain a desired acidity of the
electrodeposition bath. While a single example is given above, it
should be understood that any appropriate method for introducing
protons into, or forming protons in, an electrodeposition bath may
be used either continuously or at predetermined intervals to
maintain the desired acidity of the electrodeposition bath.
[0030] Without wishing to be bound by theory, as described herein,
ionic liquids, such as chloraluminate ionic liquids, are Lewis
acids due to the presence of Lewis acidic (electron accepting)
species such as Lewis acidic aluminum species. Additionally, the
protons (H.sup.+) present in the electrodeposition bath are
Bronsted acids (proton donation). Similarly, the aromatic
hydrocarbons that accept the protons are Bronsted bases (proton
accepting).
[0031] In some instances it may be desirable to reduce the acidity
(i.e. decrease the H.sup.+ concentration) of a non-aqueous
electrodeposition bath. For example, a particular leveling additive
being used in an electrodeposition process may not function
appropriately if the electrodeposition bath becomes too acidic. In
such an embodiment, a sufficiently basic non-protonated aromatic
hydrocarbon may be added to the electrodeposition bath to react
with the protons (H.sup.+) and form protonated aromatic
hydrocarbons. This reaction with the protons in the non-aqueous
electrodeposition bath may reduce the acidity of the bath. In some
embodiments, the now protonated aromatic hydrocarbons may also
provide an additional function as leveling additives in the
electrodeposition bath as noted above.
[0032] Examples of appropriate aromatic hydrocarbons which are
useful as protonated leveling additives include 4-tertbutyltoluene,
4-isopropyltoluene, 1,4-diisopropylbenzene, mesitylene,
1,2,4,5-tetramethylbenzene, 1,2,3-tetramethylbenzene,
pentamethylbenzene, hexamethylbenzene, tertbutylbenzene,
1,3,5-tritertbutylbenzene, 3,5-ditertbutyltoluene, benzethonium
chloride, anthracene, 9,10-dimethylanthracene, 2-methylanthracene,
9-ethylanthracene, 1,2-benzanthracene, acenapthene, naphthacene,
pyrene, 3,4-benzopyrene, perylene, polystyrene,
4-tertbutylpolystyrene, and polyethoxylated alkyl phenols (Trade
names: Triton X-100, IGEPAL CA-210, IGEPAL CO-520, IGEPAL CO-890,
IGEPAL DM-970 and others). While specific aromatic hydrocarbons are
noted above, it should be understood that the current disclosure is
not limited to only these compounds. Instead, the current
disclosure should be read generally as applying to any appropriate
aromatic hydrocarbon that is sufficiently basic to be capable of
forming a protonated species that functions as a leveling additive
in a non-aqueous electrodeposition bath.
[0033] Several general structures that may form protonated aromatic
hydrocarbons include, but are not limited to, the following
structures.
##STR00001##
[0034] In the above noted structures, the each incidence of a
substituent R is independently selected from alkyls, aryls, and
polyalkoxy chains. Additionally, the number of substituents n can
range from 0 to (2z+4) where z is the number of rings, or any other
appropriate number of substituents. Additionally, depending on the
embodiment, the number of rings may be 1, 2, 3, 4, or any
appropriate number of rings as the disclosure is not so
limited.
[0035] It should be understood that the desired concentration of an
aromatic hydrocarbon within a particular non-aqueous
electrodeposition bath may depend on the particular non-aqueous
liquids present within the bath, the types of materials being
deposited, the deposition currents and voltages, and other
considerations. Therefore, the use of the leveling additives
described herein should not be limited to any particular
concentration range. However, in some embodiments, a leveling
additive may have a concentration greater than about 0.5 wt. %, 1
wt. %, 2 wt. %, 3 wt. %, 4 wt. %, or 5 wt. %. Similarly, the
leveling additive may have a concentration less than about 10 wt.
%, 9 wt. %, 8 wt. %, 7 wt. %, 6 wt. %, or 5 wt. %. Combinations of
the above ranges are possible. For example, the leveling additives
described herein may be present in the electrodeposition bath in a
concentration between about 0.5 wt. % to 10 wt. %. The above noted
weight percentages are given relative to the non-aqueous liquid,
which in some embodiments is an ionic liquid, present in the
electrodeposition bath. Additionally, concentrations both greater
than and less than those noted above are also contemplated.
[0036] As noted above, the leveling additives may be deprotonated
through a reduction reaction during electrodeposition. However, the
leveling additives may also be reprotonated by reacting with acidic
protons in the electrodeposition bath. The percentage of leveling
additive in the protonated state will be dependent on the reduction
rate and reprotonation rate of the leveling additive. In view of
the above, in some embodiments, it may be desirable to maintain a
sufficient electrodeposition bath acidity, i.e. acidic proton
concentration, to maintain a particular amount of the leveling
additive in protonated form. The particular concentrations
necessary to maintain a desired amount of the leveling additive in
its protonated state will vary depending on the particular leveling
additive being used, the rate at which the leveling additive
deprotonates, as well as various electrodeposition operating
parameters. However, in some embodiments, the proton concentration
is selected such that at least a majority of the leveling additive,
i.e. more than 50%, is maintained in its protonated state. For
example, in one embodiment, the proton concentration is selected
such that the percentage of leveling additive in the protonated
state is between about 70% and 99%. In other embodiments, the
percentage of the leveling additive in the protonated state may be
greater than about 70%, 80%, or 90%. Similarly, the percentage of
the leveling additives in the protonated state may be less than
about 99%, 90%, or 80%. Combinations of the above ranges are
envisioned. While particular percentages of the leveling additive
in the protonated state are provided above, percentages both
greater than and less than those noted above are contemplated.
[0037] The protonated aromatic hydrocarbons used as leveling
additives may be used at any appropriate temperature. For example,
the leveling additives may be used between the electrodeposition
bath melting temperature and a temperature corresponding to the
stability limit of the leveling additive. For example, a leveling
additive might be used at temperatures that are greater than about
10.degree. C., 20.degree. C., 50.degree. C., 100.degree. C., or any
other appropriate temperature. In one particular embodiment, the
operating temperature is less than about 150.degree. C.
corresponding to the stability limit of the carbon ring in the
aromatic hydrocarbon. In such an embodiment, the electrodeposition
bath might be operated at temperatures between about 10.degree. C.
and 150.degree. C. While particular temperatures are given above,
it should be understood that other temperatures both greater than
and less than those noted above are also contemplated.
[0038] It should be appreciated that the aromatic compounds, as
described herein, may be substituted with any number of
substituents which confer suitable properties (i.e. basicity) to
permit the additive to exist in a protonated form in a non-aqueous
electrodeposition bath. That is, any of the above noted groups may
be optionally substituted. As used herein, the term "substituted"
is contemplated to include all permissible substituents of organic
compounds, "permissible" being in the context of the chemical rules
of valence known to those of ordinary skill in the art. In general,
the term "substituted" whether preceded by the term "optionally" or
not, and substituents contained in formulas of this disclosure,
refer to the replacement of hydrogen radicals in a given structure
with the radical of a specified substituent. When more than one
position in any given structure may be substituted with more than
one substituent selected from a specified group, the substituent
may be either the same or different at every position. It will be
understood that "substituted" also includes that the substitution
results in a stable compound, e.g., which does not spontaneously
undergo transformation such as by rearrangement, cyclization,
elimination, etc. In some cases, "substituted" may generally refer
to replacement of a hydrogen with a substituent as described
herein. However, "substituted," as used herein, does not encompass
replacement and/or alteration of a key functional group by which a
molecule is identified, e.g., such that the "substituted"
functional group becomes, through substitution, a different
functional group. In a broad aspect, the permissible substituents
include acyclic and cyclic, branched and unbranched, carbocyclic
and heterocyclic, aromatic and nonaromatic substituents of organic
compounds. Illustrative substituents for the aromatic hydrocarbons
described herein include, but are not limited to: alkyls, aryls,
and polyalkoxy chains. For purposes of this disclosure, the
heteroatoms such as nitrogen may have hydrogen substituents and/or
any permissible substituents of organic compounds described herein
which satisfy the valencies of the heteroatoms. Furthermore, this
disclosure is not intended to be limited in any manner by the
permissible substituents of organic compounds.
[0039] As used herein, "aromatic hydrocarbon" refers to monocyclic
or polycyclic (e.g., bicyclic, tricyclic, etc. . . . ) unsaturated
hydrocarbon having from 6 to 18 carbon atoms ("C.sub.6-18 aromatic
hydrocarbon"), 6 to 22 carbon atoms ("C.sub.6-22 aromatic
hydrocarbon"), or any other appropriate number of carbon atoms.
Unless otherwise specified, each instance of an aromatic
hydrocarbon is independently unsubstituted (an "unsubstituted
aromatic hydrocarbon") or substituted (a "substituted aromatic
hydrocarbon") with one or more substituents. In certain
embodiments, the aromatic hydrocarbon is an unsubstituted
C.sub.6-18 aromatic hydrocarbon. In certain embodiments, the
aromatic hydrocarbon is a substituted C.sub.6-18 aromatic
hydrocarbon. In some embodiments, the aromatic hydrocarbon is a
substituted or unsubstituted C.sub.6-22 aromatic hydrocarbon.
[0040] As used herein, "alkyl" refers to a radical of a
straight-chain or branched saturated hydrocarbon group having from
1 to 18 carbon atoms ("C.sub.1-18 alkyl"). In some embodiments, an
alkyl group has 1 to 9 carbon atoms ("C.sub.1-9 alkyl"). Unless
otherwise specified, each instance of an alkyl group is
independently unsubstituted (an "unsubstituted alkyl") or
substituted (a "substituted alkyl") with one or more substituents.
In certain embodiments, the alkyl group is an unsubstituted
C.sub.1-18 alkyl (e.g., --CH.sub.3). In certain embodiments, the
alkyl group is a substituted C.sub.1-18 alkyl. In some embodiments,
the alkyl group is a substituted or unsubstituted C.sub.12-16 alkyl
group. Without wishing to be bound by theory, a longer tail may
help to provide a bifunctional molecule capable of orienting a
hydrophobic tail group away from the negatively charged cathode
during electrodeposition. However, any of the above alkyl groups
may still be used.
[0041] As used herein, "aryl" refers to a radical of a monocyclic
or polycyclic (e.g., bicyclic, tricyclic, etc. . . . ) 4n+2
aromatic ring system (e.g., having 6, 10, or 14 r electrons shared
in a cyclic array) having 6-14 ring carbon atoms and zero
heteroatoms provided in the aromatic ring system ("C.sub.6-14
aryl"). "Aryl" also includes ring systems wherein the aryl ring is
fused with one or more carbocyclyl or heterocyclyl groups wherein
the radical or point of attachment is on the aryl ring, and in such
instances, the number of carbon atoms continue to designate the
number of carbon atoms in the aryl ring system. Unless otherwise
specified, each instance of an aryl group is independently
unsubstituted (an "unsubstituted aryl") or substituted (a
"substituted aryl") with one or more substituents. In certain
embodiments, the aryl group is an unsubstituted C.sub.6-14 aryl. In
certain embodiments, the aryl group is a substituted C.sub.6-14
aryl.
[0042] As used herein, a "polyalkoxy chain" refers to a substituent
group including 1 to 40 repeating units of an alkyl group bonded to
an oxygen atom. For example, a polyalkoxy chain might include a
polymethoxy chain including (CH.sub.3O--) units or a polyethoxy
chain including (CH.sub.2CH.sub.2O--) units. In some embodiments, a
polyalkoxy chain terminates in an --OH group. However, embodiments
in which a polyalkoxy chain terminates in an alkyl, aryl,
substituted phenol, or quaternary ammonium group instead of an --OH
group are also contemplated. While any length polyalkoxy chain may
be used, in some embodiments, the polyalkoxy chain includes between
or equal to 5 and 10 repeating units. Without wishing to be bound
by theory, polyalkoxy chains with these lengths may be more readily
dissolved within a nonaqueous electrodeposition bath. Unless
otherwise specified, each instance of a polyalkoxy chain is
independently unsubstituted (an "unsubstituted polyalkoxy chain")
or substituted (a "substituted polyalkoxy chain") with one or more
substituents.
[0043] The above noted leveling additives and methods may be used
with any appropriate non-aqueous electrodeposition bath. However,
in one embodiment, the electrodeposition bath includes an ionic
liquid with one or more metal ionic species. The electrodeposition
bath may also include one or more appropriate co-solvents.
Appropriate ionic liquid, metal ionic species, and co-solvents are
described in more detail below. The metal ionic species present in
the bath may be selected for depositing pure metals or alloys as
the disclosure is not so limited.
[0044] Non-limiting examples of types of metal ionic species
include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Rh,
Ru, Ag, Cd, Pt, Pd, Ir, Hf, Ta, W, Re, Os, Li, Na, K, Mg, Be, Ca,
Sr, Ba, Ra, Zn, Au, U, Al, Si, Ga, Ge, In, Tl, Sn, Sb, Pb, Bi, and
Hg. In one specific embodiment, the metal ionic species include at
least aluminum or aluminum and manganese for depositing pure
aluminum and an aluminum manganese alloy respectively. The metal
ionic species may be provided in any suitable amount relative to
the total bath composition. Additionally, the metal ionic species
may be provided in any appropriate form. For example, aluminum
might be provided in the form of an aluminum chloride (AlCl.sub.3)
added to the electrodeposition bath.
[0045] Those of ordinary skill in the art will be aware of suitable
ionic liquids to use in connection with the electrodeposition baths
and methods described herein. The term "ionic liquid" as used
herein is given its ordinary meaning in the art and refers to a
salt in the liquid state. In embodiments wherein an
electrodeposition bath comprises an ionic liquid, this is sometimes
referred to as an ionic liquid electrolyte. The ionic liquid
electrolyte may optionally comprise other liquid components, for
example, a co-solvent, as described herein. An ionic liquid
generally comprises at least one cation and at least one anion. In
some embodiments, the ionic liquid comprises an imidazolium,
pyridinium, pyridazinium, pyrazinium, oxazolium, triazolium,
pyrazolium, pyrrolidinium, piperidinium, tetraalkylammonium or
tetraalkylphosphonium salt. In some embodiments, the cation is an
imidazolium, a pyridinium, a pyridazinium, a pyrazinium, a
oxazolium, a triazolium, or a pyrazolium. In some embodiments, the
ionic liquid comprises an imidazolium cation. In some embodiments,
the anion is a halide. In some embodiments, the ionic liquid
comprises a halide anion and/or a tetrahaloaluminate anion. In some
embodiments, the ionic liquid comprises a chloride anion and/or a
tetrachloroaluminate anion. In some embodiments, the ionic liquid
comprises tetrachloroaluminate or
bis(trifluoromethylsulfonyl)imide. In some embodiments, the ionic
liquid comprises butylpyridinium, 1-ethyl-3-methylimidazolium
[EMIM], 1-butyl-3-methylimidazolium [BMIM],
benzyltrimethylammonium, 1-butyl-1-methylpyrrolidinium,
1-ethyl-3-methylimidazolium, or trihexyltetradecylphosphonium. In
some embodiments, the ionic liquid comprises
1-ethyl-3-methylimidazolium chloride. In one specific embodiment a
chloroaluminate ionic liquid such as [EMIM]Cl/AlCl.sub.3 and/or
[BMIM]Cl/AlCl.sub.3 may be used in the electrodeposition bath.
[0046] In some embodiments, the co-solvent is an organic solvent
which may, or may not be, an aromatic solvent. In some embodiments,
the co-solvent is selected from the group consisting of toluene,
benzene, tetralin (or substituted versions thereof), ortho-xylene,
meta-xylene, para-xylene, mesitylene, halogenated benzenes
including chlorobenzene and dichlorobenzene, and methylene
chloride. In some embodiments, the co-solvent is toluene. The
co-solvent may be present in any suitable amount. In some
embodiments, the co-solvent is present in an amount between about 1
vol % and 99 vol %, between about 10 vol % and about 90 vol %,
between about 20 vol % and about 80 vol %, between about 30 vol %
and about 70 vol %, between about 40 vol % and about 60 vol %,
between about 45 vol % and about 55 vol %, or about 50 vol % versus
the total bath composition. In some embodiments, the co-solvent is
present in an amount greater than about 50 vol %, 55 vol %, 60 vol
%, 65 vol %, 70 vol %, 80 vol %, or 90 vol % versus the total bath
composition. In some embodiments, the co-solvent and the ionic
liquid form a homogenous solution.
[0047] The specific co-solvent to be used may be selected based
upon any number of desired characteristics including, for example,
viscosity, conductivity, boiling point, and other characteristics
as would be apparent to one of ordinary skill in the art.
[0048] One or more co-solvents may be mixed with the ionic liquid
in any desired ratio to provide the desired electrodeposition bath
properties. For example, in some embodiments, the co-solvent may
also be selected based on its boiling point. In some cases, a
higher boiling point co-solvent may be employed as it can reduce
the amount and/or rate of evaporation from the electrolyte, and
thus, may aid in stabilizing the process. Those of ordinary skill
in the art will be aware of the boiling points of the co-solvents
described herein (e.g., toluene, 111.degree. C.; methylene
chloride, 41.degree. C.; 1,2-dichlorobenzene, 181.degree. C.;
o-xylene, 144.degree. C.; and mesitylene, 165.degree. C.). While
specific co-solvents and their boiling points are listed above,
other co-solvents are also possible. Furthermore, in some
embodiments the co-solvent is selected based upon multiple criteria
including, but not limited to, conductivity, boiling point, and
viscosity of the resulting electrodeposition bath.
[0049] Turning now to the figures, several non-limiting embodiments
of leveling additives, their methods of use, and methods for
regenerating an electrodeposition bath are discussed in more
detail.
[0050] FIG. 1 shows an electrodeposition system 10 according to an
embodiment. System 10 includes a electrodeposition bath 12. An
anode 14 and cathode 16 are provided in the bath. The bath may
include metal sources either in the form of metal ionic species
added directly to the bath and/or the anode itself may be used as a
source for the metal ionic species present in the bath that are
used for electrodepositing a metal layer on the cathode. The bath
may also include one or more additives and/or co-solvents as
described herein. A power supply 18 is connected to the anode and
the cathode. During use, the power supply generates a waveform
which creates a voltage difference between the anode and cathode.
The voltage difference leads to reduction of metal ionic species in
the bath which deposit in the form of a coating on the cathode, in
this embodiment, which may also function as the deposition
substrate in some embodiments. It should be understood that the
illustrated system is not intended to be limiting and may include a
variety of modifications as known to those of skill in the art.
[0051] Without wishing to be bound by theory, the proposed basic
aromatic hydrocarbons function as proton-addition complexes within
a non-aqueous electrodeposition bath, such as a chloroaluminate
ionic liquid bath. For example, FIG. 2 depicts a protonation
reaction of anthracene (C.sub.14H.sub.10) with a proton (H.sup.+)
located within the electrodeposition bath. In the depicted
embodiment, the compound accepts the positively charged proton to
form a protonated anthracene (C.sub.14H.sub.11).sup.+. The now
protonated aromatic hydrocarbon is a charged cation that may
interact strongly with the negatively charged cathode during the
electrodeposition process. The leveling additive consequently forms
a surface active layer on the deposition surface which suppresses
electrodeposition in regions of high current density which may
result in more level deposits. However, and without wishing to be
bound by theory, during electrodeposition, part or all of the
protonated aromatic hydrocarbons may themselves be
electrochemically reduced. Such a reaction is shown in FIG. 3 where
a protonated arene ring of the protonated anthracene
(C.sub.14H.sub.11).sup.+ loses a proton by reacting with an
electron (e.sup.-) to form anthracene (C.sub.14H.sub.10) and
hydrogen gas (H.sub.2).
[0052] Once a leveling additive has been deprotonated, the additive
is no longer a positively charged cation. Therefore, the additive
may not be attracted towards the cathode and thus would not behave
as a leveling additive. However, the additive may be protonated
again by a chemical reaction with protons (H.sup.+), which may be
introduced into the electrodeposition bath in any number of ways.
Since reduction of the protonated leveling additive may occur
continuously during electrodeposition, the introduction of acid
into the bath may either be carried out continuously or in batches
as the disclosure is not so limited.
[0053] In one embodiment, a dry gaseous acid, such as HCl, may be
bubbled through the electrodeposition bath to introduce protons
without introducing additional water to the non-aqueous
electrodeposition bath.
[0054] In another embodiment, the electrodeposition bath may be
replenished by carrying out a controlled hydrolysis of compounds
including hydroxyl (--OH) groups added to the electrodeposition
bath to produce an acid, such as HCl. Compounds containing hydroxyl
groups may be added to the electrodeposition bath in a number of
ways including, but not limited to, the measured addition of
H.sub.2O to the electrodeposition bath, as a liquid, or as a solid
hydrate. While any appropriate hydrate may be used, in some
instances, the hydrate may be selected to correspond with the
electrodeposition bath chemistry. For example, AlCl.sub.3.6H.sub.2O
might be used for an electrodeposition bath including a
chloroaluminate ionic liquid. Similarly, alumina, silica, and/or
other materials compatible with the electrodeposition bath that
include surface hydroxyl groups capable of reacting to form an
acid, such as HCl, may be added to the electrodeposition bath.
These materials may be provided in any appropriate form including,
but not limited to, powders, particles, foams, flakes, and/or any
other appropriate form as the disclosure is not so limited. After
reacting with the electrodeposition bath, in some embodiments, the
remaining material may be filtered out of the electrodeposition
bath using any appropriate method. An example of an alumina powder
including a surface hydroxyl group reacting with a chloroaluminate
ionic liquid to form HCl is provided below. While a particular
reaction is shown below, it should be understood that any number of
reactions capable of forming different acids in the
electrodeposition bath might be used.
Al.sub.2O.sub.3--OH[surf]+Al.sub.xCl.sub.y.fwdarw.Al.sub.2O.sub.3--O--Al-
.sub.xCl.sub.(y-1)[surf]+HCl
[0055] In another embodiment, protons are added to the
electrodeposition bath through a chemical reaction of a compound
including a hydroxyl group with a component of the
electrodeposition bath. In one specific embodiment, cellulose,
which may be in the form of cellulose powder or any other
appropriate form, is added to a non-aqueous electrodeposition bath
to form an acid therein. In instances where the electrodeposition
bath includes a chloroaluminate ionic liquid, HCl is formed in the
electrodeposition bath according to the reaction provided
below.
[C.sub.6H.sub.7O.sub.2(OH).sub.3].sub.n+3(n)Al.sub.xCl.sub.y.fwdarw.[C.s-
ub.6H.sub.7O.sub.2(OAl.sub.xCl.sub.(y-1)).sub.3].sub.n+3(n)HCl
[0056] U.S. patent application Ser. No. 13/830,521, filed on Mar.
14, 2013, entitled "Electrodeposition in Ionic Liquid
Electrolytes," is incorporated by reference in its entirety for all
purposes including electrodeposition bath chemistries,
electrodeposition systems, and electrodeposition methods. In
instances where the disclosure of the current application and a
reference incorporated by reference conflicts, the current
disclosure controls.
[0057] Depending on the particular compound being protonated, an
electrodeposition bath may change colors according to the amount of
protonated leveling additive present in the bath. For example, some
protonated leveling additives may exhibit a yellow or red color.
Therefore, in some embodiments, an intensity of the coloration, or
conversely the amount of absorption, at a particular wavelength may
be used to determine the amount of protonated leveling additive in
a bath which may then be used to adjust and/or control the
regeneration rate of the bath. FIG. 4 presents an overlay of
several ultraviolet/visible spectra that exhibit increasing
absorption at a wavelength of about 460 nm for an electrodeposition
bath including increasing concentrations of protonated
4-tertbutyltoluene species in an ionic liquid/toluene bath.
Example: Batch Electrodeposition Bath Regeneration
[0058] A 40 ml bath containing [EMIM].Al.sub.2Cl.sub.7 ionic
liquid, 0.4 wt. % MnCl.sub.2, 50 vol. % toluene as a co-solvent,
and 2 wt. % 4-tertbutyltoluene as a leveling additive, was used to
plate aluminum-manganese alloy on a copper substrate. The above
noted weight percentages are given relative to the ionic liquid
weight. The initial HCl concentration of the ionic liquid was
sufficient to protonate about 75-100% of the tert-butyltoluene
present in the bath, as confirmed by separate experiments. The
electrodeposition was carried out using a reverse pulse technique.
The electrodeposited samples were 40 .mu.m thick. The appearance of
the samples served as an indicator of the additive activity.
[0059] In this example, the electrodeposition bath was regenerated
after every 10 Ah/L by adding about 0.175 mMol of HCl to the
electrodeposition bath. This amount was selected to be enough to
protonate about 10% of the tert-butyltoluene present within the
electrodeposition bath.
[0060] Initially, 4-tertbutyltoluene was considered to be
protonated by the HCl initially present in the ionic liquid. As
shown in FIG. 5A, the electrodeposited alloy initially formed a
smooth shiny surface during the initial plating. As the plating
continued, the additive slowly deprotonated, and the samples become
more matte in appearance as shown for the samples corresponding to
electrodeposition from aged electrodeposition baths containing
reduced levels of the protonated additive, see FIG. 5A.
[0061] After 10 Ah/l, the additive was regenerated with the
indicated amount of HCl. For regeneration, a part of the bath
solution was brought into contact with a silica gel powder, which
reacted with the ionic liquid to form HCl. The silica was then
filtered out, and the solution was mixed back into the bath. The
plating was then continued for another 10 Ah/l, then the bath was
regenerated again. FIG. 5B shows the electrodeposited samples with
increasing electrodeposition bath age after the first bath
regeneration. Similar to the initial electrodeposition, the
electrodeposited alloy initially formed a smooth shiny surface
during the initial deposition which proceeded to a more matte
appearance with increasing time indicating deprotonation of the
additive. The process was repeated for a third time and similar
results were obtained, see FIG. 5C.
[0062] In view of the successful regeneration of the
electrodeposition bath using HCl, it is possible to restore the
activity of the leveling additive by reprotonating the leveling
additive already present within the bath without the need to add
any additional leveling additive.
Example: Continuous Electrodeposition Bath Regeneration
[0063] An electrodeposition bath and plating process similar to
that described above was prepared. However, in this example, the
bath regeneration was carried out continuously by adding smaller
amounts of HCl to the bath during electrodeposition. The same
methods for adding the HCl to the bath as used in the prior example
were employed in this example as well. The resulting samples versus
increasing electrodeposition bath age for the first 20 Ah/l are
shown in FIG. 6. As shown in the figure, the appearance of the
samples did not noticeably change during this experiment, although
the amount of HCl added to the electrodeposition bath per Ah/l was
equivalent to that added in the prior example. Therefore,
continuous regeneration of the leveling additive is a viable method
for maintaining the electrodeposition bath.
[0064] While the present teachings have been described in
conjunction with various embodiments and examples, it is not
intended that the present teachings be limited to such embodiments
or examples. On the contrary, the present teachings encompass
various alternatives, modifications, and equivalents, as will be
appreciated by those of skill in the art. Accordingly, the
foregoing description and drawings are by way of example only.
* * * * *