U.S. patent application number 10/225677 was filed with the patent office on 2003-01-16 for electrolytic copper plating solutions.
Invention is credited to Barstad, Leon R., Lefebvre, Mark, Martin, James L., Menard, Stephane, Rychwalski, James E., Schetty, Robert A. III, Toben, Michael.
Application Number | 20030010646 10/225677 |
Document ID | / |
Family ID | 23214138 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030010646 |
Kind Code |
A1 |
Barstad, Leon R. ; et
al. |
January 16, 2003 |
Electrolytic copper plating solutions
Abstract
The present invention provides inter alia copper electroplating
compositions, methods for use of the compositions and products
formed by the compositions. Electroplating compositions of the
invention contain an increased brightener concentration that can
provide effective copper plate on difficult-to-plate aperture
walls, including high aspect ratio, small diameter microvias.
Inventors: |
Barstad, Leon R.; (Raynham,
MA) ; Rychwalski, James E.; (Medway, MA) ;
Lefebvre, Mark; (Hudson, NH) ; Menard, Stephane;
(Lyon, FR) ; Martin, James L.; (Merrick, NY)
; Schetty, Robert A. III; (Fort Saloga, NY) ;
Toben, Michael; (Smithtown, NY) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP.
P.O. BOX 9169
BOSTON
MA
02209
US
|
Family ID: |
23214138 |
Appl. No.: |
10/225677 |
Filed: |
August 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10225677 |
Aug 22, 2002 |
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09313045 |
May 17, 1999 |
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6444110 |
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Current U.S.
Class: |
205/291 ;
205/293; 205/295; 205/298 |
Current CPC
Class: |
C25D 3/38 20130101; C25D
5/48 20130101; H05K 3/423 20130101 |
Class at
Publication: |
205/291 ;
205/298; 205/293; 205/295 |
International
Class: |
C25D 003/38; C25D
003/40 |
Claims
What is claimed:
1. A copper electroplating composition comprising: at least one
soluble copper salt, an electrolyte, and one or more brightener
compounds that are present in a concentration of at least about 1.5
mg per liter of the electroplating composition.
2. The composition of claim 1 wherein the concentration of the
brightener agent is at least about 2 mg per liter of the
electroplating composition.
3. The composition of claim 1 wherein the concentration of the
brightener agent is at least about 4 mg per liter of the
electroplating composition.
4. The composition of claim 1 wherein the concentration of the
brightener agent is at least about 10 mg per liter of the
electroplating composition.
5. The composition of claim 1 wherein the concentration of the
brightener agent is at least about 25 mg per liter of the
electroplating solution.
6. The composition of claim 1 wherein the one or more brightener
compounds contain one or more sulfur atoms.
7. The composition of claim 1 wherein the one or more brightener
compounds comprise one or more sulfide or sulfonic acid groups.
8. The composition of claim 1 wherein the one or more brightener
compounds comprise a group of the formula R'--S--RSO.sub.3 where R
is optionally substituted alkyl, optionally substituted
heteroalkyl, optionally substituted aryl, optionally substituted
heteroaromatic, or optionally substituted heteroalicyclic; and R'
is hydrogen or a chemical bond.
9. The composition of claim 1 wherein the composition further
comprises a suppressor agent.
10. The composition of claim 9 wherein the suppressor agent is a
polyether.
11. The composition of claim 1 wherein the composition further
comprises a leveler agent.
12. The composition of claim 1 wherein the electroplating
composition is acidic.
13. A method for plating an electronic device substrate containing
one or more apertures, the method comprising: electrolytically
depositing onto the substrate copper from an electroplating
composition that comprises at least one soluble copper salt, an
electrolyte, and one or more brightener compounds that are present
in a concentration of at least about 1.5 mg per liter of the
electroplating composition.
14. The method of claim 13 wherein the brightener concentration is
at least about 2 mg per liter of the electroplating solution.
15. The method of claim 13 wherein the brightener concentration is
at least about 10 mg per liter of the electroplating solution.
16. The method of claim 13 wherein the substrate is a printed
circuit board substrate or semiconductor with one or microvias.
17. The method of claim 16 wherein the one or more microvias have
an aspect ratio of at least about 4:1 and diameters of at least
about 200 nm.
18. The method of claim 17 wherein copper is deposited to fill the
one or more microvias to provide a copper plate in the absence of
voids or inclusions.
19. The method of claim 17 wherein the composition further
comprises a suppressor agent.
20. The method of claim 13 wherein the substrate is a microchip
module substrate.
21. An article of manufacture comprising an electronic device
substrate containing one or more apertures each having walls, the
aperture walls having thereon an electrolytic copper deposit
obtained from an electroplating composition that comprises at least
one soluble copper salt, an electrolyte, and one or more brightener
compounds that are present in a concentration of at least about 1.5
mg per liter of the electroplating composition.
22. The article of claim 21 wherein the substrate is printed board
substrate, a microchip module substrate, or a semiconductor chip
substrate.
23. The article of claim 21 wherein the substrate comprises the one
or more microvias that have an aspect ratio of at least about 4:1
and diameters of at least about 200 nm, and the walls of the one or
more microvias have a copper deposit that is free of voids.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present 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 increased
brightener levels and use of same for effective plating of high
aspect ratio apertures, e.g. microvias with aspect ratios of at
least 4:1 and diameters of 200 nm or smaller.
[0003] 2. Background
[0004] Electroplating articles with copper coatings is generally
well known in the industry. Electroplating methods involve passing
a current between two electrodes in a plating solution where one
electrode 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 copper sulfate), (2) an acidic electrolyte
(such as sulfuric acid) in an amount sufficient to impart
conductivity to the bath and (3) additives (such as surfactants,
brighteners, levelers and suppressants) to enhance the
effectiveness and quality of plating. See generally U.S. Pat. Nos.
5,668,013; 5,174,886; 5,051,154; 3,876,513; and 5,068,013 for a
discussion of copper plating baths.
[0005] Over time, a number of improvements in electroplating
techniques have been made as the articles to be plated evolved in
degree of difficulty and standards for plating increased. However,
even with the improvements in electroplating techniques,
circumstances exist that can lead to plating defects.
[0006] Copper plating technology has been particularly important in
the manufacture of computer circuit boards. More specifically,
during circuit board manufacture, copper electrical connections are
provided between various board layers by plating board through
holes whereby a thin conductive copper conductive is first applied,
typically using electroless copper plating techniques, followed by
electroplating copper from acid copper Solutions.
[0007] Copper plating is also employed in circuit board manufacture
to plate outer layers where final circuitry is defined. For such
applications, panel plating is typically employed, where the full
circuit board surface is copper plated followed by photodefining
circuitry with a photoresist and then etching in a subtractive
process. Alternatively an additive process can be employed, where
copper circuits are produced by plating between lines defined by a
resist relief image.
[0008] More recently, copper plating also has been employed in
semiconductor chip manufacture to provide chip interconnections.
Traditionally, semiconductors have been interconnected through
aluminum conductors. However, industry continually demands enhanced
performance, including ultra large-scale integration and faster
circuits. Consequently, chip interconnects are required at
dimensions of 200 nm and less. At such geometries, the resistivity
of aluminum (theoretically 2.65.times.10.sup.-8 ohm/meter at room
temperature) is considered too high to allow the electronic signal
to pass at required speeds. Copper, with a theoretical resistivity
of 1.678.times.10.sup.-8 ohm/meter, is considered a more suitable
material to meet the next generation of semiconductor
microchips.
[0009] Typical processes for defining semiconductor chip
interconnects, particularly aluminum interconnects, have involved
reactive ion etching of metal layers, e.g. a process that includes
metal deposition, photolithographic patterning, line definition
through reactive ion etching and dielectric deposition. However, in
Cu-based systems, reactive ion etching is not practical as a result
of the paucity of copper compounds with vapor pressures sufficient
to enable removal of the copper as may be desired.
[0010] Consequently, alternative strategies have developed, such as
the Damascene process. That process starts with deposition of
dielectric typically by chemical vapor deposition of silicon
materials or organic dielectrics followed by curing, or spin
coating silicon materials or organic dielectrics. Patterning by
photolithographic processes and reactive ion etching defines the
vias and trenches (interconnects) in the dielectric.
[0011] Barrier layers are then formed by chemical vapor deposition
or other methods to isolate the copper lines from the dielectric.
Copper is then deposited and excess material removed by chemical or
mechanical polishing processes.
[0012] Although conventional copper plating systems can be suitable
for plating vias and trenches as small as 300 nm with 4:1 aspect
ratios, defects such as seams, voids and inclusions can occur with
conventional methods when attempting to plate features that are
smaller or have higher aspect ratios. Such defects can occur as a
result of conformal copper plating, i.e. where all targeted
surfaces are plated at the same rate such that the sidewalls of a
via or trench plate together forming a seam or a demarcation of
disruption where the copper grains are separated and will not
anneal to form a continuous copper wire. Defects also will occur at
the top rim of a via hole, where electronic charge density can
concentrate and result in rapid copper growth that closes off the
via before the via is filled sufficiently with metal. Such
inadequate metal fill can result in inclusion and voids, disrupting
the ability of the plated metal to carry a coherent signal.
[0013] It thus would be desirable to have new electroplating
compositions. It would be particularly desirable to have new copper
electroplating compositions that can plate effectively (e.g.
absence of voids, inclusions and seams) high aspect ratio
apertures, including high aspect ratio microvias as discussed
above.
SUMMARY OF THE INVENTION
[0014] We have now found copper electroplating compositions that
effectively plate a wide variety of articles, including printed
circuit boards and other electronic packaging devices. Compositions
and methods of the invention are particularly useful for filling
microvias and trenches required by current and anticipated
semiconductor fabrication requirements (including microvias having
aspect ratios of at least 4:1 and diameters of 200 nm or less) by
reliably plating copper deposits that are essentially or completely
free of voids, inclusions or other plating imperfections.
[0015] Electroplating baths of the invention are characterized in
significant part by comprising enhanced brightener concentrations.
Without being bound by any theory, it is believed that the higher
brightener concentrations can accelerate the plating rate in
recesses and microvias as carrier molecules become incorporated
into the plating deposit. This is counterintuitive to conventional
thought and a completely unexpected result.
[0016] In particular, preferred electroplating compositions of the
invention have a brightener concentration of at least about 1.5 mg
per liter of plating solution (1.5 mg/L), more preferably a
brightener concentration of at least about 1.75 mg per liter, still
more preferably at least about 2.0, 2.5. 3, 3.5 or 4 mg of
brightener per liter of plating solution. Good results have been
achieved with even higher brightener concentrations, e.g. copper
plating baths having a brightener concentration of at least about 5
mg per liter, or at least about 6, 7, 8, 9, 10, 12, 14, 16, 18, 20
or 25 mg/L, or even higher brightener concentrations such as at
least about 30, 35, 40, 45, 50, 55 or 60 mg of brightener per liter
of plating solution.
[0017] Preferably, the brightener concentration is maintained at
such high concentrations throughout the entire or at least
substantial portion of a plating cycle. Such maintenance of
brightener concentrations entails regular addition of brightener
during a plating cycle as the brightener component plates out.
Brightener concentrations and replenishment rates during a plating
cycle can be readily determined by known methods, such as the CPVS
method as disclosed in U.S. Pat. Nos. 5,252,196 and 5,223,118, both
assigned to the Shipley Company, or by the cyclic voltammetric
stripping (CVS) methods.
[0018] In addition to such an elevated brightener concentration,
preferably the plating bath also contains a surfactant-type
suppressor agent. It has been surprisingly found that use of such a
suppressor agent in combination with elevated brightener
concentrations can result in effective "bottom-fill" copper plating
of a microvia or other aperture without defects such as inclusions
or voids. In particular, the suppressor enables enhanced plating
rate at the bottom of a microvia, permitting copper to plate the
entire aperture space in a substantially "bottom-fill" manner,
without premature sealing of the aperture top that can result in
inclusions or voids.
[0019] The invention also includes articles of manufacture,
including electronic packaging devices such as printed circuit
boards, multichip modules, semiconductor integrated circuits and
the like that contain a copper deposit produced from a plating
solution of the invention. Other aspects of the invention are
discussed infra
DETAILED DESCRIPTION OF THE INVENTION
[0020] Compositions of the invention suitably contain a copper
salt, an electrolyte preferably an acidic aqueous solution such as
a sulfuric acid solution with a chloride or other halide ion
source, and one or more brightener agents in enhanced
concentrations as discussed above, and preferably a suppressor
agent. The plating compositions also may contain other components
such as one or more leveler agents and the like.
[0021] As discussed above, electroplating solutions of the
invention are particularly effective in plating various articles
having microvias with high aspect ratios and small diameters. In
particular, solutions of the invention are useful in plating
electronic packaging 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 microvias of such electronic
devices without the defects exhibited upon use of prior
chemistries. In addition, the invention has application to plating
on a wide variety of other polymer and metal substrates.
[0022] Electroplating solutions of the invention generally comprise
at least one soluble copper salt, an electrolyte and a brightener
component. More particularly, electroplating compositions of the
invention preferably contain a copper salt; an electrolyte,
preferably an acidic aqueous solution such as a sulfuric acid
solution with a chloride or other halide ion source; and one or
more brightener agents in enhanced concentrations as discussed
above. Electroplating compositions of the invention also preferably
contain a suppressor agent. The plating compositions also may
contain other components such as one or more leveler agents and the
like.
[0023] A variety of copper salts may be employed in the subject
electroplating solutions, including for example copper sulfates,
copper acetates, copper fluoroborate, and cupric nitrates. Copper
sulfate pentahydrate 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 of 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.
[0024] 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, particularly a
chloride ion source. Examples of suitable acids for the electrolyte
include sulfuric acid, acetic acid, fluoroboric acid, methane
sulfonic acid and sulfamic acid. Sulfuric acid is generally
preferred. Chloride is a generally preferred halide ion. 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 100 parts per million (ppm) of halide ion in the
plating solution, more preferably from about 25 to about 75 ppm of
halide ion source in the plating solution.
[0025] The invention also includes electroplating baths that are
substantially or completely free of an added acid and may be
neutral or essentially neutral (e.g. pH of at least less than about
8 or 8.5). Such plating compositions are suitably prepared in the
same manner with the same components as other compositions
disclosed herein but without an added acid. Thus, for instance, a
preferred substantially neutral plating composition of the
invention may have the same components as the plating bath of
Example I which follows, but without the addition of sulfuric
acid.
[0026] As discussed above, it has been discovered that by
increasing brightener concentration beyond conventional levels,
uniform plating of particularly high aspect ratio microvias and
other difficult-to-plate apertures is now possible.
[0027] In particular, copper electroplating compositions are
provided that have a brightener agent concentration of at least
about 1.5 mg per liter of plating solution (1.5 mg/L), compared to
typical brightener concentrations ranging from about 0.05 to 1.0
mg/L in prior composition. More preferably, in electroplating baths
of the invention, the brightener concentration is at least about
1.75 mg/L, and still more preferably, at least about 2, 2.5, 3, 3.5
or 4 mg/L. Even higher brightener concentrations will be suitable
or even preferred, e.g. at least about 10, 15, 20, 30, 40, 50 mg of
brightener per liter of plating solution. A brightener
concentration of from about 20 to about 200 mg per liter of plating
solution will be suitable for many applications.
[0028] Preferably, the brightener concentration is maintained
throughout the entire electroplating process, or throughout at
least a substantial portion of the plating process, e.g. at least
about 50, 60, 70, 80 or 90 percent of the duration of the plating
process. As discussed above, since brightener levels are depleted
as the electroplating progresses, the brightener component is
preferably regularly replenished during plating to maintain a
steady state brightener concentration.
[0029] A wide variety of brighteners, including known brightener
agents, may be employed in the copper electroplating compositions
of the invention. Typical brighteners contain one or more sulfur
atoms, and typically without any nitrogen atoms and a molecular
weight of about 1000 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--SO.sub.3X, 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 sodium or potassium;
and R' is hydrogen or a chemical bond (i.e. --S--R--SO.sub.3X or
substituent of a larger compound). Typically alkyl groups will have
from one to about 16 carbons, more typically one to about 8 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. Carbocyclic
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, O or S atoms and 1-3 separate or
fused rings and include e.g. coumarinyl, qulinolinyl, 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, O or S atoms and from 1 to 3 separate or fused rings
and include e.g. tetrahydrofuranyl, thienyl, tetrahydropyranyl,
piperdinyl, morpholino, pyrrolindinyl, and the like. Substituents
of substituted alkyl, heteroalkyl, aryl or heteroalicyclic groups
include e.g. C.sub.1-8 alkoxy; C.sub.1-8 alkyl, halogen,
particularly F, Cl and Br; cyano, nitro, and the like.
[0030] More specifically, useful brighteners include those of the
following formulae:
XO.sub.3 S--R--SH
XO.sub.3S--R--S--S--R--SO.sub.3 X and
XO.sub.3S--Ar--S--S--Ar--SO.sub.3X
[0031] 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 sodium or potassium.
[0032] Some specific suitable brighteners include e.g.
n,n-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid (sodium salt); carbonic
acid-dithio-o-ethylester-s-ester with 3-mercapto-l-propane sulfonic
acid (potassium salt); bissulfopropyl disulfide;
3-(benzthiazolyl-s-thio)propy- l sulfonic acid (sodium salt);
pyridinium propyl sulfobetaine;
1-sodium-3-mercaptopropane-l-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-sulfonopropyl-disulfide.
[0033] In addition to the copper salts, electrolyte and brightener,
plating baths of the invention optionally may contain a variety of
other components, including organic additives such as suppressors
agents, leveling agents and the like.
[0034] As discussed above, use of a suppressor agent in combination
with an enhanced brightener concentration is particularly preferred
and provides surprisingly enhanced plating performance,
particularly in bottom-fill plating of small diameter and/or high
aspect ratio microvias.
[0035] 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
microvia as a result of diffusion effects through the length of the
microvia. That reduced suppressor concentration results in an
enhanced copper plating rate at the microvia bottom regions.
[0036] In contrast, at the surface of the article to be plated (at
the top of the microvia), the suppressor agent concentration
remains relatively constant and at an elevated level relative to
the microvia bottom regions. Consequently, the area at a microvia
top has a comparatively suppressed plating rate because of the
enhanced suppressor agent concentration relative to the microvia
bottom regions.
[0037] Preferred suppressor agents for use in the compositions of
the invention are polymeric materials, preferably s having hetero
atom substitution, particularly oxygen linkages. Generally
preferred suppressor agents ate generally high molecular weight
polyethers, such as those of the following formula:
R--O--(CXYCX'Y'O).sub.nH
[0038] 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;
aralkyl 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 12,000.
[0039] More specifically, 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. 300,000 to 4 million); block
copolymers of polyoxyalkyenes; alkylpolyether sulfonates;
complexing surfactants such as alkoxylated diamines; and complexing
agents for cupric or cuprous ions which include entprol, citric
acid, edetic acid, tartaric acid, potassium sodium tartrate,
acetonitrile, cupreine and pyridine.
[0040] Particularly suitable surfactants for plating compositions
of the invention are commercially available polyethylene glycol
copolymers, including polyethylene glycol copolymers. Such polymers
are available from e.g. BASF (sold by BASF under Tetronic and
Pluronic tradenames), and copolymers from Chemax. A
butylalcoholethylene oxide-propylene oxide copolymer having an
M.sub.w of about 1800 from Chemax is particularly preferred.
[0041] Surfactants are typically added to copper electroplating
solutions in concentrations ranging from about 1 to 10,000 ppm
based on the weight of the bath, more preferably about 5 to 10,000
ppm.
[0042] Use of one or more leveling agents in plating baths of the
invention is generally preferred. Examples of 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. 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 6 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.
[0043] 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; quaternized,
acrylic, polymeric amines; polyvinyl carbamates; pyrrolidone; and
imidazole. A particularly preferred leveler is
1-(2-hydroxyethyl)-2-imida- zolidinethione. Typical concentrations
of leveling agents range from about 0.05 to 0.5 mg per liter of
plating solution.
[0044] The copper electroplating compositions are suitably used in
similar manner as prior copper electroplating baths, except an
elevated brightener concentration is employed and preferably
maintained at an elevated level throughout a plating cycle.
[0045] For instance, with reference to a printed circuit board
substrate, a copper clad plastic substrate is typically employed,
e.g. a copper clad glass fiber reinforced epoxy panel. Prior to
formation of a circuit, apertures, such as microvias, are formed in
the board by drilling and metallization. Microvias and other
apertures also may be formed by photoimaging. Processes for forming
such apertures in electronic device substrates are known and are
disclosed e.g. in U.S. Pat. No. 4,902,610; C. Coombs, Printed
Circuits Handbook, (4.sup.th ed., McGraw Hill); and T. Kiko,
Printed Circuit Board Basics (PMS Indus.).
[0046] After formation of the microvia or other aperture,
electroless plating procedures are then used to form a first
metallic coating over the substrate surfaces and electrolytic
copper deposition is then used to enhance the thickness of the
coating. Alternatively, electrolytic copper may be plated directly
over a suitably prepared microvia as disclosed in any of U.S. Pat.
Nos. 5,425,873; 5,207,888; and 4,919,768. The next step in the
process comprises electroplating copper onto the thus prepared
conductive microvias using an electroplating solution of the
invention.
[0047] Plating baths of the invention are preferably employed at or
above room temperature, e.g. up to and somewhat above 65.degree. C.
The plating composition is preferably agitated during use such as
by air sparger, work piece agitation, impingement or other suitable
method. Plating is preferably conducted at a current ranging from 1
to 40 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.
[0048] 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, high
aspect ratio microvias and other apertures. The plating
compositions of the invention also will be particularly useful for
plating integrated circuit devices, such as formed semiconductor
devices and the like. See the examples which follow for exemplary
substrates plated in accordance with the invention.
[0049] As discussed above, aspect ratios of at least 4:1, having
diameters of about 200 nm or smaller have been effectively copper
plated with no defects (e.g. no voids or inclusions by ion beam
examination) using plating solutions of the invention. Microvias
with diameters below 150 nm, or even below about 100 nm, and aspect
ratios of 5:1, 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
by ion beam examination) using plating solutions of the
invention.
[0050] All documents mentioned herein are fully incorporated herein
by reference. The following non-limiting examples are illustrative
of the invention.
EXAMPLE 1
[0051] A preferred copper electroplating bath of the invention was
prepared by admixing the following components in water. In the
composition the brightener was bis-sodium-sulfonopropyl-disulfide
and the suppressor was a polyethylene glycol polymer sold under the
tradename PEG 8000 by Union Carbide.
1 Component Concentration CuSO.sub.45H.sub.2O 60 g/l
H.sub.2SO.sub.4 225 g/l Cl 50 ppm Suppressor 1 g/l Brightener 2.1
mg/l
[0052] Through hole walls of a printed circuit board substrate and
microvias were plated as follows with the above plating
composition. An air-agitated plating tank outfitted with multiple
cathode rails and one rectifier was charged with the above copper
plating solution. During plating, the following deposition
conditions were employed:
[0053] current density of 14.5 mA/cm.sup.2; waveform was DC;
temperature plating bath was 25.degree. C. After termination of the
plating procedure, a microvia of the board substrate was examined.
It was found that copper completely filled the microvia walls to
provide a smooth uniform copper plate with no voids.
EXAMPLE 2
[0054] A further preferred copper electroplating bath of the
invention was prepared by admixing the following components in
water. In the composition the brightener was
bis-sodium-sulfonopropyl-disulfide and the suppressor was a
propylene glycol copolymer sold under the tradename L62D by
BASF.
2 Component Concentration CuSO.sub.45H.sub.2O 70 g/l
H.sub.2SO.sub.4 175 g/l Cl 50 ppm Suppressor 0.875 g/l Brightener
2.4 mg/l
[0055] 200 nm with 7:1 aspect ratio microvias of a back end of the
line semiconductor microchip wafer were plated using the above
plating composition. The wafer was electrically attached to a
cathode and the plating solution was pumped onto the surface of the
wafer while rotating at upwards of 200 RPM. Electrical current of
14.5 mA/cm.sup.2 was applied with DC wave form at 25.degree. C.
After termination of the plating procedure, the microvias were
filled with no defects as determined by focused ion beam
examination.
EXAMPLE 3
Comparative Example
[0056] A further preferred copper electroplating bath of the
invention was prepared by admixing the following components in
water. In the composition the brightener was
bis-sodium-sulfonopropyl-disulfide and the suppressor was a
propylene glycol copolymer sold under the tradename L62D by
BASF.
3 Component Concentration CuSO.sub.45H.sub.2O 60 g/l
H.sub.2SO.sub.4 225 g/l Cl 50 ppm Suppressor 1 g/l Brightener 0.35
mg/l
[0057] 200 nm with 4:1 aspect ratio microvias of a semiconductor
microchip wafer were plated using the above comparative plating
composition under conditions as described in Example 2. After
termination of the plating procedure, the microvias were examined
by scanning electron microscopy (SEM) and focused ion beam
examination. Those examinations showed the copper deposits in the
microvias contained defects of voids, seams and inclusions.
[0058] 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.
* * * * *