Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROLYTIC COPPER PLATING SOLUTIONS
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of United States Provisional
Application
Serial No. 60/403,954, filed August 16, 2002.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates to copper electroplating solutions, methods for
using the
solutions and products formed by using such methods and solutions. More
particularly, the
invention provides electrolytic copper plating solutions that have sulfonic
acid anions and use
of same for effective plating of electronic features such as trenches and vias
with aspect ratios
of about 1:1 and diameters of 1 to 500 microns.
Description of the Prior Art
[0003] Electroplating articles with copper coatings is well known in the
industry.
Electroplating methods involve passing a current between two electrodes in a
plating solution
where one electrode, the cathode, is the article to be plated. A common
plating solution
would be an acid copper plating solution containing (1) a dissolved copper
salt such as cupric
sulfate, (2) an acid typically of the same anion used with the copper salt
such as sulfuric acid
in an amount sufficient to impart conductivity to the electrolyte and (3)
additives such as
surfactants, brighteners, levelers and suppressants to enhance the
effectiveness and quality of
plating. See generally U.S. Pat. Nos. 5,068,013; 5,174,886; 5,051,154 and
5,068,013 for a
discussion of copper plating baths.
[0004] Commercial copper solutions include copper sulfate, copper
pyrophosphate,
copper fluoroborate and copper cyanide. Copper sulfate and fluoroborate
solutions are
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typically used at medium and high current densities whereas copper
pyrophosphate and
copper cyanide are used to deposit copper at low to medium current densities.
Because of
health concerns associated with handling cyanide and fluoroboric acid and
waste-treatment
concerns with pyrophosphate, the most widely used commercial copper plating
solution is
copper sulfate. Copper sulfate solutions are used to deposit a copper coating
on substrates
such as printed circuit boards, automobile parts and household fixtures. The
copper ion
concentration varies from about 10 grams per liter to about 75 grams per
liter. The sulfuric
acid concentration may very from about 10 grams per liter to about 300 grams
per liter.
Copper plating for electronic components usually use low copper metal
concentrations and
high free acid concentrations.
[0005] The use of sulfonic acids in electroplating has been described
previously.
[0006] Proell, W. A. in U.S. Patent # 2,525,942 claims the use of
alkanesulfonic acid
electrolytes in electroplating. However, only mixed alkanesulfonic acids were
used and only
specific claims were made for lead, nickel, cadmium, silver and zinc.
[0007] Proell, W. A in U.S. Patent # 2,525,943 specifically claims the use of
alkanesulfonic acid electrolytes in copper electroplating. However, only mixed
alkanesulfonic acids were used and the exact composition of the mixture was
not disclosed.
[0008] Proell, W. A.; Faust, C. L.; Agruss, B.; Combs, E. L. in The Monthly
Review
of the American Electroplaters Society 1947, 34, 541-9 describes preferred
formulations for
copper plating from mixed alkanesulfonic acid based electrolytes. Again,
however, only
mixed alkanesulfonic acids were used.
[0009] Dahms, W. and Wunderlich, C. in a German Patent # 4,338,148 discloses a
methanesulfonate-based copper plating system which incorporates organic sulfur
compounds
as additives.
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(0010] Jiqing, Cai, Diandu Yu Huanbao 1995, 15(2), 20-2 dislcosed some
benefits of
using methanesulfonate-based acid copper plating formulations. The greatest
benefit was stated
to be superior surface cleaning and etching prior to the actual plating step.
[0011] Bernards, R. F.; Fisher, G.; Sonnenberg, W.; Cerwonka, E. J.; Fisher
S., U.S.
Patent # 5,051,154, describes surface active additives for copper plating with
only minor mention
of MSA as one of a number of possible electrolytes. However, no examples
employing MSA are
included.
(0012] Andricacos, P. C., Chang, I. C., Hariklia, D. and Horkans, J. in U.S.
Patent #
5,385,661 discuss a process which allows for the electrodeposition of Cu
alloys containing small
amounts of tin and lead via under-potential deposition. The patent discloses
MSA is
exceptionally well suited for allowing this type of process to occur properly,
owing mostly to the
weakly complexing nature of methanesulfonic acid/methanesulfonate. A paper on
this subject (J.
Electrochem. Soc.; 1995; 142(7); 2244-2249) was also published.
[0013] Recently, copper plating has been used in semiconductor chip
manufacture to
provide chip interconnections. Semiconductors have been interconnected through
aluminum
conductors. However, industrial advances calls for enhanced performance,
including ultra large-
scale integration (ULSI) and faster circuits with interconnects as small as
200 nm and less. At
these small feature sizes, the resistivity of aluminum is too high to allow
the electronic signal to
pass at required speeds. Copper has an inherently small resistivity and as
such is a more suitable
metal to meet the demand for next generation of semiconductor devices.
[0014] Typical processes for aluminum interconnects in semiconductor chips may
involve ion etching of metal layers, e.g. a process that includes metal
deposition,
photolithographic patterning, line definition through reactive ion etching and
dielectric
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deposition. Use of copper in advanced interconnects precludes the use of
reactive ion etching
due to the paucity of copper compounds with vapor pressures sufficient to
enable removal of the
copper as may be desired.
(0015] The damascene process has evolved in the semiconductor industry as a
method to
pattern and deposit metal in-laid structures into electronic features such as
trenches and vias.
The damascene process starts with deposition of dielectric usually by chemical
vapor deposition
of silicon materials or organic dielectrics followed by curing, or spin
coating silicon materials or
other inorganic or organic dielectrics. Patterning is next done using
photolithographic processes
and then reactive ion etching defines the vias and trenches (interconnects) in
the dielectric.
Barrier layers made from refractory-type materials are deposited into the
features using a
chemical vapor deposition method. A thin copper seed layer is deposited on the
barrier layer to
impart conductivity to the features. This is followed by copper electroplating
to fill the small
features. Excess copper and barrier layer materials may be removed by chemical
or mechanical
polishing processes.
[0016] Several improvements in electroplating solutions and techniques have
been made
as the small electronic features to be plated evolved in degree of difficulty
and standards for
plating increased. Even with the improvements in electroplating processes,
circumstances may
exist that can lead to plating defects due to inadequate copper fill in the
vias or trenches or
through-holes. These defects are incomplete fill in the via or through-hole
(e.g., dimples),
overplating (e.g., mounds above the features), inclusion of non-metals and
voids (e.g., holes in
the copper coating).
[0017] Although conventional copper plating systems can be suitable for
plating vias and
trenches as larges as 1 micron and even larger such as 1 to 500 microns with
aspect ratios
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varying from less than 1:1 to about 5:1, defects such as dimples, overplates,
seams, voids and
inclusions can occur with conventional copper electrolytes and methods when
attempting to plate
features that are relatively small or low to moderate aspect ratios. These
defects can occur as a
result of conformal copper plating, i.e., where all surfaces that must be
plated with copper at the
same rate. Defects may also arise due to non-conformal fill as a result of
inadequate wetting of
the electronic features by the copper plating solution, adsorption of gas
bubbles on the side walls
of the features, too rapid of plating rates of the features leading to over-
plate structures due to
non-uniform adsorption of the sulfur-containing accelerating agent or dimples
in the copper fill
deposit because of preferential adsorption of the suppressor additive in the
vias or through-holes.
[0018] It thus would be desirable to have new electroplating compositions. It
would be
particularly desirable to have new copper electroplating compositions that can
plate copper
effectively (e.g., absence of dimples, overplates, voids, inclusions and
seams) in low (<3:1)
aspect ratio apertures, including trenches and vias or through-holes.
SUMMARY OF THE INVENTION
[0019] Copper electroplating compositions have been found that effectively
plate a wide
variety of articles, including integrated circuits such as those with
damascene structures, printed
circuit boards and other electronic packaging devices.
(0020] Compositions of the invention contain a copper alkanesulfonate salt and
free
alkanesulfonic acid, wherein the free acid has a concentration from about 0.05
to about 2.50 M.
The compositions additionally may contain an halide ion, and, optionally, one
or more additives
such as a suppressor agent, a brightener agent, a leveler agent or a
surfactant. The compositions
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are intended for the metallization of micron-sized dimensioned trenches or
vias, through-holes
and microvias.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The compositions and methods of the invention are particularly useful
for filling
vias, microvias and trenches and through-holes required by today's and future
semiconductor
and printed circuit board fabrication requirements (including vias having
aspect ratios of at least
0.5:1 and up to 4:1 and diameters of 0.5 microns to about 500 microns or more)
by reliably
plating copper deposits from electrolytes containing sulfonate anions (and
other acid anions such
as sulfate) that are essentially or completely free of dimples, overplates,
voids, inclusions or
other plating imperfections.
[0022] The present invention has found that it is better to use a pure
alkanesulfonate
solution rather than the mixed sulfonate solutions of the prior art since the
shorter chain
alkanesulfonates have been found to deposit better at higher free acid
concentration and the
longer carbon chain sulfonates work better at lower free acid.
[0023] The alkanesulfonic acids are distinguished from sulfuric acid by their
unique balance
of physical properties. For instance, the surface tension lowering capability
of the alkanesulfonic
acids increases up with chain length. However, so also does a general decrease
in the aqueous
solubility of metal alkanesulfonates go up with chain length.
[0024] The most preferred embodiment of the invention focuses on the
unexpected
superiority of C~ to C3 alkanesulfonic acids and derivatives thereof as
electrolytes for copper
electroplating. These acids have the best balance of metal alkanesulfonate
solubility and surface
tension lowering capability. The lower surface tension of the alkanesulfonates
increases the
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surface activity which is important for plating into micron-dimensioned holes,
while the metal
salt solubility is important for plating generally. The solution conductivity
of the sulfonic acids
are generally lower than those based on sulfuric acid at an equivalent free
acid concentration.
This lower conductivity results in a shift in the primary current density
distribution to low
current density areas on the article to be plated with copper resulting in a
more uniform copper
deposit. Based on theory, the invention can be altered by the use of C~ to C3
alkanesulfonic acid
derivatives.
[0025] Electroplating baths of the invention are characterized in significant
part by
comprising a high concentration of a sulfonate anion (RS03-). Without being
bound by any
theory, it is believed that the high sulfonate anion concentrations can
modulate the plating rate in
recesses such as vias, trenches and through-holes. This is counterintuitive to
conventional
thought and completely unexpected since the sulfonate anion is chemically
similar to the
accelerator type-additives used in many commercial acid copper electrolytes.
Such accelerator
anions usually have a sulfur moiety and a sulfonic acid moiety on the same
molecule similar to
the sulfonate anion. However, instead of accelerating copper deposition into
the small features
on electronic components leading to defects such as dimples or overplate
structures like the
sulfur-containing accelerator additive, the sulfonate molecule modulates
copper deposition
leading to a more uniform, defect-free copper deposit.
[0026] In particular, preferred electroplating compositions of the invention
have a sulfonate
concentration of at least about 0.05 mol/liter, more preferably a sulfonate
concentration of at
least about 0.2 mol/liter, still more preferably at least about 0.4 mol to
about 1.0 mol/liter of
plating solution. Adequate results have been achieved with even higher
sulfonate concentrations,
e.g. copper plating baths having a sulfonate concentration of at least about
2.25 mol/liter.
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[0027] Preferably, the sulfonate anion concentration is maintained at such
high
concentrations throughout the entire or at least a substantial portion of a
plating cycle. A portion
of the acid anion may be another acid anion molecule such as sulfate,
fluoroborate, sulfamate,
acetate, phenylsulfonate, phenolsulfonate, tolylsulfonate, phosphonate and
pyrophosphate.
[0028] In addition to a sulfonate anion, the plating bath may also contains
other additives
commonly used in acid copper electrolytes such as suppressor additives,
brighteners,
accelerators, levelers and a surfactant-type agent. It has been surprisingly
found that use of such
a sulfonate acid anion combination with suppressors, accelerators, brighteners
and levelers can
result in effective "bottom-up fill" copper plating of a via or trench or
other electronic features
such as through holes in printed circuit boards without defects such as
dimples, overplate,
inclusions, seams or voids.
[0029] In particular, the sulfonate acid anion enables modulated plating rates
at the bottom
of a electronic feature, permitting copper to plate the entire aperture in a
substantially "bottom-
fill" fashion, without 1) resulting in low copper deposition in the middle of
the aperture (e.g.,
dimples), 2) premature sealing of the aperture top that can result in
inclusions or voids and 3)
overplating the aperture resulting in overplate structures that must be
subsequently mechanically
and chemically removed.
[0030] The invention also includes articles of manufacture, including
electronic packaging
devices such as printed circuit boards, multichip modules, semiconductor
integrated circuits,
mechanical-electronic machine devices (i.e., MEMS devices) and the like that
contain a copper
deposit produced from a plating solution of the invention. Other aspects of
the invention are
discussed infra.
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[0031] As discussed above, electroplating solutions of the invention are
particularly
effective in plating various electronic articles having vias, microvias,
trenches or through-holes
with low (0.5:1 to 3:1) aspect ratios.
[0032] In particular, solutions of the invention are useful in plating
electronic devices such
as printed circuit boards, microchip module packaging and blind 3-dimensional
structures,
particularly semiconductor integrated circuits and other circuit systems. The
electroplating
solutions of the invention are particularly useful to copper fill vias and
microvias and through-
holes of such electronic devices without defects commonly found with the use
of prior
chemistries based on non-sulfonate chemistries.
[0033] Preferred electroplating solutions of the invention generally comprise
at least one
soluble copper salt, an acid electrolyte, a halogen ion and additives.
[0034] More particularly, electroplating compositions of the invention
preferably contain a
copper salt of an alkyl or aryl sulfonic acid; an electrolyte, preferably an
acidic aqueous solution
such as a sulfonic acid solution with a chloride or other halide ion source;
and one or more
additives such as a brightener agent, a suppressor agent and a leveler agent
and the like.
[0035] A variety of copper alkane salts may be employed in the subject
electroplating
solutions wherein the alkanesulfonic acid of the anionic portion of the copper
salt and any free
acid are introduced as an alkyl or aryl sulfonic acid of formula:
R"c
Ra - C -(SOZOH)y
R'b
wherein a+b+c+y equals 4;
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R, R' and R" are the same or different and each independently may be hydrogen,
phenyl, Cl, F,
Br, I, CF3 or a lower alkyl group such as (CHZ)n where n is from 1 to 7,
preferably 1 to 3, and
that is unsubstituted or substituted by oxygen, Cl, F, Br, I, CF3, -SOZOH.
Preferred alkyl
sulfonic acid are methanesulfonic, ethanesulfonic and propanesulfonic acids
and the alkyl
polysulfonic acids are methanedisulfonic acid, monochloromethanedisulfonic
acid,
dichloromethanedisulfonic acid, 1,1-ethanedisulfonic acid, 2-chloro-1,1-
ethanedisulfonic acid,
1,2-dichloro-1,1-ethanedisulfonic acid, 1,1-propanedisulfonic acid, 3-chloro-
1,1-
propanedisulfonic acid, 1,2-ethylene disulfonic acid, 1,3-propylene disulfonic
acid,
trifluormethanesulfonic acid, butanesulfonic acid, perfluorobutanesulfonic
acid, pentanesulfonic,
and the aryl sulfonic acids are phenylsulfonic, phenolsulfonic and
tolylsulfonic acids .
[0036] Other copper salts may also be in the copper electrolyte such as copper
sulfate,
copper acetate, copper fluoroborate, copper sulfamate, cupric nitrates or
copper phosphonates.
Copper methanesulfonate is a particularly preferred copper salt. A copper salt
may be suitably
present in a relatively wide concentration range in the electroplating
compositions of the
invention. Preferably, a copper salt will be employed at a concentration from
about 10 to about
300 grams per liter of plating solution, more preferably at a concentration of
from about 25 to
about 200 grams per liter of plating solution, still more preferably at a
concentration of from
about 40 to about 175 grams per liter of plating solution.
[0037] Additionally, in the present invention it has been found that a
concomitant
decrease in free acid with an increase in the carbon chain length produces
defect-free deposits.
The ethanesulfonic and propanesulfonic acid solutions operate best at lower
free acid
concentrations, less than 1.50 M free acid. The lower free acid concentrations
minimizes
corrosion of the copper seed-layer leading to less defects in the
electroplated copper layer. The
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sulfonates also deposit a smoother copper coating compared to sulfuric acid.
The
trifluormethanesulfonate solutions yields commercially acceptable coatings
over a wide free acid
concentration range not disclosed by Proell.
[0038] The electrolyte may also contain free acid to increase solution
conductivity. The
preferred free acid has the same anion as the copper salt anion but mixtures
of free acids are also
within the scope of this invention. Preferred alkyl sulfonic acid are
methanesulfonic,
ethanesulfonic and propanesulfonic acids and the alkyl polysulfonic acids are
methanedisulfonic
acid, monochloromethanedisulfonic acid, dichloromethanedisulfonic acid, 1,1-
ethanedisulfonic
acid, 2-chloro-1,1-ethanedisulfonic acid, 1,2-dichloro-1,1-ethanedisulfonic
acid, 1,1-
propanedisulfonic acid, 3-chloro-1,1-propanedisulfonic acid, 1,2-ethylene
disulfonic acid, 1,3-
propylene disulfonic acid, trifluormethanesulfonic acid, butanesulfonic acid,
perfluorobutanesulfonic acid, pentanesulfonic acid and the aryl sulfonic acids
are phenylsulfonic
and tolylsulfonic acids. The free acid concentration ranges from about 1 g/1
to about 300 g/1,
more preferably at a concentration of from about 25 to about 200 grams per
liter of plating
solution, still more preferably at a concentration of from about 40 to about
175 grams per liter of
plating solution.
[0039] The invention also includes electroplating baths that are substantially
or
completely free of an added sulfonic acid and may be neutral or essentially
neutral (e.g. pH of at
least less than about 7 or 7.5). Such plating compositions are suitably
prepared in the same
manner with the same components as other compositions disclosed herein but
without an added
sulfonic acid.
[0040] Plating baths of the invention preferably employ an acidic electrolyte,
which
typically will be an acidic aqueous solution and that preferably contains a
halide ion source,
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particularly a chloride ion source. Examples of other suitable halides include
bromide and iodide.
A wide range of halide ion concentrations (if a halide ion is employed) may be
suitably utilized,
e.g. from about 0 (where no halide ion employed) to 200 parts per million
(ppm) of halide ion in
the plating solution, more preferably from about 10 to about 75 ppm of halide
ion source in the
plating solution.
[0041] In addition to the copper salts, acid electrolyte and a halogen ion,
plating baths of
the invention optionally may contain a variety of other components, including
organic additives
such as suppressors agents, accelerator agents, leveling agents and the like.
The use of a
suppressor agent in combination with a accelerator or brightener additive is
particularly preferred
and provides surprisingly enhanced plating performance, particularly in bottom-
fill plating of
small diameter and/or low to moderate aspect ratio vias or microvias and
through-holes.
[0042] Without being bound by any theory, it is believed such enhanced bottom-
fill
plating may occur due to the concentration of the suppressor agent being
comparatively
decreased at a bottom of a via or microvia or within the through-holes as a
result of diffusional
effects through the length of the via, microvia or through-hole. The reduced
suppressor additive
concentration results in an enhanced copper plating rate at the bottom
portions of the via,
microvia regions or in the middle of the trough-hole. At the surface of the
feature to be plated (at
the top of the via or microvia or the surface of the printed circuit board),
the suppressor agent
concentration remains relatively high and constant relative to the via,
microvia bottom regions or
in the middle of the through-hole. Therefore, the top area of the feature to
be plated has a
comparatively suppressed or slowed plating rate because of the enhanced
suppressor agent
concentration relative to the bottom portion of the article being plated with
copper. Preferred
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suppressor agents for use in the compositions of the invention are polymeric
materials,
preferably having hetero-atom substitution, particularly oxygen linkages.
[0043] Preferred suppressor agents are high molecular weight polyethers, such
as those
of the following formula:
R-O-(CXYCX'Y'O)nH
where R is an aryl or alkyl group containing from about 2 to 20 carbon atoms;
each X, Y, X' and
Y' is independently hydrogen; alkyl preferably methyl, ethyl or propyl; aryl
such as phenyl; aryl
such as benzyl, and preferably one or more of X, Y, X' and Y' is hydrogen; and
n is an integer
between 5 and 100,000. Preferably, R is ethylene and n is greater than 5,000
and less than
75,000.
[0044] As discussed above, it has been discovered that by having a high
sulfonate anion
concentration, beyond conventional levels of typical accelerator type-
additives, uniform plating
of particularly low to high aspect ratio vias and microvias and other
difficult-to-plate electronic
features such as through-holes in printed circuit boards is now possible.
[0045] A wide variety of brighteners, including known brightener agents, may
be
employed in the copper electroplating compositions of this invention. Typical
brighteners
contain one or more sulfur atoms, and typically without any nitrogen atoms and
a molecular
weight of about 1500 or less. Brightener compounds that have sulfide and/or
sulfonic acid
groups are generally preferred, particularly compounds that comprise a group
of the formula R'-
S-R-S03X, where R is an optionally substituted alkyl (which include
cycloalkyl), optionally
substituted heteroalkyl, optionally substituted aryl group, or optionally
substituted
heteroalicyclic; X is a counter ion such as ammonium, sodium or potassium; and
R' is hydrogen
or a chemical bond (i.e. -S-R~S03X or substituent of a larger compound).
Typically alkyl groups
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will have from one to about 20 carbons, more typically one to about 6 or 12
carbons.
Heteroalkyl groups will have one or more hetero (N, O or S) atoms in the
chain, and preferably
have from 1 to about 16 carbons, more typically 1 to about 8 or 12 carbons.
Carboxcyclic aryl
groups are typical aryl groups, such as phenyl and naphthyl. Heteroaromatic
groups also will be
suitable aryl groups, and typically contain 1 to about 3 N, 0 or S atoms and 1-
3 separate or fused
rings and include e.g. coumarinyl, quinolinyl, pyridyl, pyrazinyl, pyrimidyl,
furyl, pyrrolyl,
thienyl, thiazolyl, oxazolyl, oxidizolyl, triazole, imidazolyl, indolyl,
benzofuranyl, benzothiazol,
and the like. Heteroalicyclic groups typically will have 1 to 3 N, 0 or S
atoms and from 1 to 3
separate or fused rings and include e.g. tetrahydrofuranyl, thienyl,
tetrahydro- pyranyl,
piperdinyl, morpholino, pyrrolindinyl, and the like. Substituents of
substituted alkyl,
heteroalkyl, aryl or heteroalicyclic groups include e.g. Ci_g alkoxy; C~_8
alkyl, halogen,
particularly F, CI and Br; cyano, vitro, and the like.
[0046] More specifically, useful brighteners include those of the following
formula:
X03S-R-SH
X03S-R-S-S-R-S03X and
X03-Ar-S-S-Ar-S03X
where in the above formulae R is an optionally substituted alkyl group, and
preferably is an alkyl
group having from 1 to 6 carbon atoms, more preferably is an alkyl group
having from 1 to 4
carbon atoms; Ar is an optionally substituted aryl group such as optionally
substituted phenyl or
naphthyl; and X is a suitable counter ion such as ammonium, sodium or
potassium.
[0047] Some specific suitable brighteners include e.g. n,n-dimethyl-
dithiocarbamic acid-
(3-sulfopropyl)ester; 3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester; 3-
mercaptopropylsulfonic acid (sodium salt); carbonic acid-dithio-o-ethylester-s-
ester with 3-
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mercapto-1-propane sulfonic acid (potassium salt); bissulfopropyl disulfide; 3-
(benzthiazolyl- s-
thio)propyl sulfonic acid (sodium salt); pyridinium propyl sulfobetaine; 1-
sodium-3-
mercaptopropane-1-sulfonate; sulfoalkyl sulfide compounds disclosed in U.S.
Pat. No.
3,778,357; the peroxide oxidation product of a dialkyl amino-thiox-methyl-
thioalkanesulfonic
acid; and combinations of the above. Additional suitable brighteners are also
described in U.S.
Pat. Nos. 3,770,598,4,374,709,4,376,685, 4,555,315, and 4,673,469, all
incorporated herein by
reference. Particularly preferred brighteners for use in the plating
compositions of the invention
are n,n-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester and bis-sodium-
sulfonopropyldisulfide.
(0048] Use of one or more leveling agents in plating baths of the invention is
generally
preferred. In general, useful leveling agents include those that contain a
substituted amino group
such as compounds having R-N-R', where each R and R' is independently a
substituted or
unsubstituted alkyl group or a substituted or unsubstituted aryl group.
Typically the alkyl groups
have from 1 to 8 carbon atoms, more typically from 1 to 4 carbon atoms.
Suitable aryl groups
include substituted or unsubstituted phenyl or naphthyl. The substituents of
the substituted alkyl
and aryl groups may be, for example, alkyl, halo and alkoxy. More
specifically, suitable leveling
agents include e.g. 1-(2-hydroxyethyl)-2-imidazolidinethione; 4-
mercaptopyridine; 2-
mercaptothiazoline; ethylene thiourea; thiourea; alkylated polyalkyleneimine;
phenazonium
compounds disclosed in U.S. Pat. No. 3,956,084; N-heteroaromatic rings
containing polymers;
quatenized, acrylic, polymeric amines; polyvinyl carbamates; pyrrolidone; and
imidazole. A
particularly preferred leveler is 1-(2-hydroxyethyl)-2-imidazolidinethione.
Typical
concentrations of leveling agents range from about 0.05 to 1.5 mg per liter of
plating solution.
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Suitable leveling agents are described and set forth in U.S. Pat. Nos.
3,770,598; 4,374,709;
4,376,685; 4,555,315 and 4,673,459.
[0049] Surfactants useful in the present invention include e.g. amines such as
ethoxylated
amines, polyoxyalkylene amines and alkanol amines; amides; polyglycol-type
wetting agents,
such as polyethylene glycols, polyalkylene glycols and polyoxyalkyene glycols;
high molecular
weight polyethers; polyethylene oxides (mol. wt. 100,000 to 3 million); block
copolymers of
polyoxy- alkyenes; alkylpolyether sulfonates; complexing surfactants such as
alkoxylated
diamines; Particularly suitable surfactants for plating compositions of the
invention are
commercially available polyethylene glycol copolymers, including polyethylene
glycol
copolymers. Surfactants described in US 2001/0047943A1 are particularly
preferred.
Surfactants are typically added to copper electro- plating solutions in
concentrations ranging
from about 1 to 20,000 ppm based on the weight of the bath, more preferably
about 5 to 12,000
ppm.
[0050] The invention also includes the use of complexing agents for cupric or
cuprous
ions which include monocarboxylic, dicarboxylic and tricarboxylic acid such as
citric acid,
tartaric acid, potassium sodium tartrate, oxalic acid and phosphonic acids in
the copper sulfonate
electrolyte.
[0051] The term "copper plating" as used in this specification includes the
plating of
copper and copper alloys. Copper alloys include metals from Group 1B, 2B, 3A,
3B, 4A, 4B,
SB, 6B, 7B, and 8 of the periodic table.
[0052] Plating baths of the invention are preferably employed at or above room
temperature, e.g. up to and somewhat above 65° C. The plating
composition is preferably
agitated during use such as by using an air sparger, physical movement of the
work piece,
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impingement of the solution or other suitable method. Plating is preferably
conducted at a
current ranging from 0.1 to 400 ASF depending upon substrate characteristics.
Plating time may
range from about 5 minutes to 1 hour or more, depending on the difficulty of
the work piece. See
generally the examples which follow for exemplary preferred procedures.
[0053] The invention described also includes the use of direct, pulse or
periodic current
waveforms .to effectively deposit a defect-free copper layer in the electronic
features.
[0054] The invention described may also use a soluble copper anode or an
insoluble or
inert anode material.
(0055] A wide variety of substrates may be plated with the compositions of the
invention,
as discussed above. The compositions of the invention are particularly useful
to plate difficult
work pieces, such as circuit board substrates with small diameter and low
aspect vias or through-
holes, integrated circuits with low aspect ratio vias, integrated circuits
with high aspect ration
microvias and other electronic features. The plating compositions of the
invention also will be
particularly useful for plating integrated circuit devices, such as formed
semiconductor devices
and the like.
[0056] As discussed above, low aspect ratios of at least 0.5:1 to about 3:1,
having
diameters of about 1 to 500 microns or larger have been effectively copper
plated with no
defects (e.g. no voids or inclusions as detectable by ion beam examination)
using plating
solutions of the invention. Microvias with diameters below 0.5 microns, or
even below about 0.2
microns, and aspect ratios of 4:1, 6:1,7:1, 10:1 or greater, and even up to
about 15:1 or greater
can be effectively plated (e.g. no voids or inclusions detectable by ion beam
examination) using
plating solutions of the invention.
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[0057] The foregoing description of the invention is merely illustrative
thereof, and it is
understood that variations and modifications can be effected without departing
from the scope or
spirit of the invention as set forth in the following claims. This invention
provides a novel means
of using biocides more effectively. By combining typical biocides with the
alkanolamines
described herein, one can obtain much better microbial control per unit of
biocide than is
obtainable without the alkanolamine.
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