U.S. patent application number 11/025273 was filed with the patent office on 2005-06-30 for plating bath and method for depositing a metal layer on a substrate.
This patent application is currently assigned to SHIPLEY COMPANY, L.L.C.. Invention is credited to Barstad, Leon R., Buckley, Thomas, Cobley, Andrew J., Kapeckas, Mark J., Reddington, Erik, Sonnenberg, Wade.
Application Number | 20050139118 11/025273 |
Document ID | / |
Family ID | 25516528 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139118 |
Kind Code |
A1 |
Cobley, Andrew J. ; et
al. |
June 30, 2005 |
Plating bath and method for depositing a metal layer on a
substrate
Abstract
A metal plating bath containing organic compounds that inhibit
or retard the consumption of plating bath additives. The additives
are chemical compounds that improve the brightness of the plated
metal, the physical properties of the plated metal especially with
respect to ductility and the micro-throwing power as well as the
macro-throwing power of the plating bath. The organic compounds
that inhibit or retard the consumption of additives increases the
life of the plating bath and improves the efficiency of the plating
process. The plating baths containing the organic compounds that
inhibit or retard additive consumption can be employed to plate
copper, gold, silver, palladium, platinum, cobalt, cadmium,
chromium, bismuth, indium, rhodium, ruthenium, and iridium.
Inventors: |
Cobley, Andrew J.;
(Coventry, GB) ; Kapeckas, Mark J.; (Marlborough,
MA) ; Reddington, Erik; (Ashland, MA) ;
Sonnenberg, Wade; (Edgartown, MA) ; Barstad, Leon
R.; (Raynham, MA) ; Buckley, Thomas; (Dedham,
MA) |
Correspondence
Address: |
John J. Piskorski
Edwards & Angell, LLP
P.O. Box 55874
Boston
MA
02205
US
|
Assignee: |
SHIPLEY COMPANY, L.L.C.
Marlborough
MA
|
Family ID: |
25516528 |
Appl. No.: |
11/025273 |
Filed: |
December 29, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11025273 |
Dec 29, 2004 |
|
|
|
09970171 |
Oct 2, 2001 |
|
|
|
Current U.S.
Class: |
106/1.18 ;
205/296 |
Current CPC
Class: |
C25D 3/02 20130101; H05K
3/241 20130101; C25D 3/38 20130101 |
Class at
Publication: |
106/001.18 ;
205/296 |
International
Class: |
C25D 003/38 |
Claims
1-23. (canceled)
24. A method for plating a metal on a substrate comprising:
contacting the substrate with a metal plating bath; and applying a
sufficient current density to the plating bath to deposit the metal
on the substrate; the metal plating bath comprises a salt of a
metal selected from metals consisting of copper, gold, silver,
palladium, platinum, cobalt, cadmium, chromium, bismuth, indium,
rhodium, ruthenium, and iridium, and an additive consumption
inhibiting compound having the formula: 3where R, R.sup.1, R.sup.2,
and R.sup.3 independently comprise hydrogen; halogen;
(C.sub.1-C.sub.20) linear, branched, or cyclic alkyl;
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl;
(C.sub.2-C.sub.20) linear, or branched alkynyl; silane; silyl;
--Si(OH).sub.3; --CN; --SCN; --C.dbd.NS; --SH; --NO.sub.2;
SO.sub.2H; --SO.sub.3M; --PO.sub.3M; aminyl; aminyl halide;
hydroxyaminyl; sulfonyl halide; (C.sub.1-C.sub.20)
alkyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, (C.sub.1-C.sub.12)
alkylphenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
-phenyl-O(C.sub.2-C.sub.3O)- .sub.xR.sup.6, where x is an integer
of from 1-500 and R.sup.6 is hydrogen, (C.sub.1-C.sub.4) alkyl or
phenyl; --P(R.sup.4).sub.2; acyl halide; --COR.sup.5, where R.sup.5
is --OH, or (C.sub.1-C.sub.20) linear, branched, or cyclic alkyl,
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl,
(C.sub.2-C.sub.20) linear or branched alkynyl, or
(C.sub.1-C.sub.20) linear, or branched alkoxy; or --OH with the
proviso that a carboxyl is present as a substituent on the
compound; and M is hydrogen or an alkali metal; or R.sup.1 and
R.sup.2 are taken together to form a chemical bond; or R.sup.1 and
R.sup.2 are taken together along with the atoms to which they are
attached to form a 5 to 7 membered ring, or to form a 5 to 7
membered heterocyclic ring where oxygen or nitrogen are
hetero-atoms in the ring the 5 to 7 membered ring or the 5 to 7
membered heterocyclic ring may comprise one or more carbonyl
groups; the 5 to 7 membered ring or the 5 to 7 membered
heterocyclic ring may be fused with one or more five or six memberd
rings, the one or more five or six membered rings may contain one
or more oxygen or nitrogen hetero-atoms, the fused rings may
contain a carbonyl in the ring; the 5 to 7 membered rings, the
fused five or six membered rings and the heterocyclic rings may be
unsubstituted or substituted.
25. (canceled)
26. The method of claim 24, wherein the additive consumption
inhibiting compound comprises 2,6-dihydroxybenzoic acid,
4-hydroxybenzoic acid resorcinol, 2,3-dihydroxybenzoic acid,
2,4-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid,
2,3,4-trihydroxybenzoic acid, methyl-3,4,5-trihydroxybenzoate,
methyl-2,4-dihydroxybenzoate, 4-hydroxmandelic acid monohydrate,
3-(phenylthio) acetic acid, gallic acid, 4-vinylkbenzoic acid,
3,4-dihydroxy-cinnamic, 4-methoxy cinnamic acid, 2-hydroxy cinnamic
acid, phthalic acid, trans-3-furanacrylic acid, sulfanilic acid, or
mixtures thereof.
27-28. (canceled)
29. The method of claim 24, further comprising brighteners,
levelers, hardeners, wetting agents, malleability modifiers,
ductility modifiers, deposition modifiers, suppressants, or
mixtures thereof.
30-31. (canceled)
32. A method for plating copper metal on a substrate comprising:
contacting the substrate with a copper plating bath; and applying
sufficient current density to the copper plating bath to deposit
copper metal on the substrate; the copper metal plating bath
comprises a copper salt and an additive consumption inhibiting
compound having the formula: 4where R, R.sup.1, R.sup.2, and
R.sup.3 independently comprise hydrogen; halogen;
(C.sub.1-C.sub.20) linear, branched, or cyclic alkyl;
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl;
(C.sub.2-C.sub.20) linear or branched alkynyl; sulfonyl halide;
--CN; --SCN; --C.dbd.NS; --SH; --NO.sub.2; SO.sub.2H; --SO.sub.3M;
--PO.sub.3M; --P(R.sup.4).sub.2, where R.sup.4 is hydrogen or
halogen; (C.sub.1-C.sub.20) alkyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
(C.sub.1-C.sub.12) alkylphenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
-phenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, where x is an integer of
from 1-500 and R.sup.6 is hydrogen, (C.sub.1-C.sub.4) alkyl or
phenyl; Si(OH).sub.3; silyl; silane; aminyl; aminyl halide;
hydroxyaminyl; acyl halide; --COR.sup.5, where R.sup.5 is OH, or
(C.sub.1-C.sub.20) linear, branched, or cyclic alkyl,
(C.sub.2-C.sub.20) linear, branched or cyclic alkenyl,
(C.sub.2-C.sub.20) linear, or branched alkynyl, or
(C.sub.1-C.sub.20) linear or branched alkxoy; or --OH with the
proviso that a carboxyl is present as a substituent on the compound
when hydroxyl is a substituent on the compound; the
(C.sub.1-C.sub.20) alkyl, (C.sub.2-C.sub.20) alkenyl,
(C.sub.2-C.sub.20) alkynyl and the (C.sub.1-C.sub.20) alkoxy groups
may be unsubstituted or substituted; and M is hydrogen or an alkali
metal; or R.sup.1 and R.sup.2 are taken together to form a bond; or
R.sup.1 and R.sup.2 may be taken together along with the atoms to
which they are attached to form a 5 to 7 membered ring, or to form
a 5 to 7 membered heterocyclic ring where oxygen or nitrogen are
hetero-atoms in the ring; the 5 to 7 membered ring, or the 5 to 7
membered heterocyclic ring may comprise one or more carbonyl
groups; the 5 to 7 membered ring or the 5 to 7 membered
heterocyclic ring may be fused with one or more five or six
membered rings, the one or more five or six membered rings may
contain one or more oxygen or nitrogen atoms, the fused rings may
contain a carbonyl in the ring; the 5 to 7 membered rings, the five
or six membered fused rings, and the heterocyclic rings may be
unsubstituted or substituted.
33. (canceled)
34. The method of claim 32, wherein the additive consumption
inhibiting compound comprises 2,6-dihydroxybenzoic acid,
4-hydroxybenzoic acid resorcinol, 2,3-dihydroxybenzoic acid,
2,4-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid,
2,3,4-trihydroxybenzoic acid, methyl-3,4,5-trihydroxsybenzoate,
methyl-2,4-dihydroxybenzoate, 4-hydroxymandelic acid monohydrate,
3-(phenylthio) acetic acid, gallic acid, 4-vinylbenzoic acid,
3,4-dihydroxy-cinnamic acid, 4-methoxy cinnamic acid, 2-hydroxy
cinnamic acid, pthalic acid, sulfanilic acid, trans-3-furanacrylic
acid, or mixtures thereof.
35-39. (canceled)
40. An apparatus for electroplating a substrate comprising an
electrical power source electrically connected with an insoluble
anode and a cathode such that an electrical current can pass
through the insoluble anode and the cathode, the insoluble anode
and the cathode are in contact with a metal plating bath comprising
a salt of a metal selected from the group consisting of copper,
gold, silver, palladium, platinum, cobalt, cadmium, chromium,
bismuth, indium, rhodium, iridium, and ruthenium, and an additive
consumption inhibiting compound having a formula: 5wherein R,
R.sup.1, R.sup.2 and R.sup.3 independently comprise hydrogen;
halogen; (C.sub.1-C.sub.20) linear, branched, or cyclic alkyl;
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl;
(C.sub.2-C.sub.20) linear, or branched alkynyl; halogen; sulfonyl
halide; --CN; --SCN; --C.dbd.NS; --SH; --NO.sub.2; --SO.sub.2H;
--SO.sub.3M; --PO.sub.3M; (C.sub.1-C.sub.20)
alkyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, (C.sub.1-C.sub.12)
alkylphenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
-phenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, where x is an integer of
from 1-500 and R.sup.6 is hydrogen, (C.sub.1-C.sub.4) alkyl or
phenyl; --P(R.sup.4).sub.2, where R.sup.4 is hydrogen or halogen;
silyl; silane; --Si(OH).sub.3; aminyl; aminyl halide;
hydroxyaminyl; acyl halide; --COR.sup.5, where R.sup.5 is --OH, or
(C.sub.1-C.sub.20) linear, branched or cyclic alkyl,
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl,
(C.sub.2-C.sub.20) linear or branched alkynyl, or
(C.sub.1-C.sub.20) linear or branched alkoxy; or --OH with the
proviso that when --OH is a substituent a carboxyl group is present
on the compound; the (C.sub.1-C.sub.20) alkyl, (C.sub.2-C.sub.20)
alkenyl, (C.sub.2-C.sub.20) alkynyl, and the (C.sub.1-C.sub.20)
alkoxy groups may be unsubstituted or substituted; and M is
hydrogen or an alkali metal; or R.sup.1 and R.sup.2 are taken
together to form a chemical bond; or R.sup.1 and R.sup.2 are taken
together along with the atoms to which they attached to form a 5 to
7 membered ring, or to form a 5 to 7 membered heterocyclic ring
where oxygen or nitrogen are hetero-atoms in the ring, the 5-7
membered ring may comprise one or more carbonyl groups; the 5 to 7
membered ring or the 5 to 7 membered heterocyclic ring may be fused
with one or more five or six membered rings, the one or more five
or six membered rings may contain one or more oxygen or nitrogen
atoms, the fused rings may contain a carbonyl group in the ring;
the 5 to 7 membered rings, the five and six membered rings, and the
heterocyclic rings may be unsubstituted or substituted.
41-46. (canceled)
47. The apparatus of claim 40, wherein the insoluble anode
comprises metals of cobalt, nickel, ruthenium, rhodium, palladium,
iridium, or platinum.
48. The apparatus of claim 47, wherein the insoluble anode further
comprises metals of titanium, zirconium, hafnium, vanadium,
niobium, or tantalum.
49. The apparatus of claim 48, wherein the insoluble anode further
comprises beryllium, calcium, strontium, barium, scandium, yttrium,
lanthanum, or rare earth elements.
50. (canceled)
51. The apparatus of claim 40, wherein the cathode comprises a
wiring board, an integrated circuit, an electrical contact surface,
a connector, an electrolyte foil, a silicon wafer, a
semi-conductor, a lead frame, an optoelectronic component, a solder
bump, a decorative article, a sanitary appliance, and the like.
52. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to a plating bath and
method for improving deposition of a metal on a substrate. More
specifically, the present invention is directed to a plating bath
and method for improving deposition of a metal on a substrate by
including organic compounds in the plating bath that inhibit the
degradation of plating bath additives.
[0002] Deposition of a metal on a substrate is used in a variety of
industrial applications such as electroforming, electrorefining,
manufacture of copper powder, electroplating, electroless plating
and the like. The process of plating a substrate with a metal is
used in the production of decorative articles for sanitary
appliances, automobile parts, jewelry and furniture fittings, many
electrical devices and circuits such as printed wiring and circuit
boards, electrolytic foil, silicon wafer plating, and the like.
Examples of metals that may be plated on a substrate include
copper, gold, silver, palladium, platinum, zinc, tin, nickel, lead,
cobalt and alloys thereof. Although many metals are employed in
plating in the production of decorative articles and electrical
devices, copper is one of the most common metals plated. The
electronics industry extensively employs copper as a metal in the
manufacture of printed wiring and circuit boards as well as other
electronic articles.
[0003] The electronics industry has a number of requirements for
copper deposits on printed wiring boards. For example, copper
layers can not form any cracks when subject to thermal shock
(immersed at least once for 10 sec. in liquid tin/lead solder at
288.degree. C.). In addition, the copper layers must be smooth, and
as uniformly thick at all locations of a coated surface. Also,
deposition procedures must be easy to manage and economical.
[0004] Anodes, such as copper anodes, that may decompose during
electroplating are often used in the electroplating of copper. Such
anodes are known in the industry as soluble anodes. Soluble anodes
may be in the form of plates, bars or spheres. The plates and bars
are connected to a power supply with a suitable fastening means.
The spheres come in baskets that often consist of titanium. The
spheres are connected to a power supply with suitable fastening
means. Such anodes decompose at about the same rate during
deposition as the copper is deposited from the deposition bath, the
amount of copper in the deposition solution remains about constant.
Thus, copper replenishment is not necessary.
[0005] Another type of anode is the insoluble anode. Exterior
dimensions of insoluble anodes do not change during metal
deposition process. Such anodes consist of inert materials such as
titanium or lead that can be coated with catalytic metals such as
platinum to prevent high anodic overvoltages. Insoluble anodes are
preferred over the soluble anodes in the production of printed
wiring and circuit boards. Electroplating processes employing
insoluble anodes are more versatile than those using consumable
electrodes, permit higher plating speeds, require smaller apparatus
size, ease of maintenance, improved solution flow and agitation and
allow anodes to be placed close to the cathodes. Particularly
advantageous is the fact that the insoluble anode does not change
size (i.e., cell geometry remains fixed). Thus, more uniform
plating results are obtained. In addition, copper salts used to
provide a source of copper are often available as products of
etching procedures associated with the production of copper plated
devices. For example, in the production of circuit boards, a copper
layer is put down over an entire surface of an insulating substrate
and part of the copper etched off to produce the circuit board of
interest.
[0006] Plating metal on a substrate, such as electroplating with
copper, is used extensively in a variety of manufacturing
procedures. Copper plating is used to prevent corrosion on various
surfaces (i.e., iron surfaces), as a binding layer for additional
metal layers, to increase electrical or thermal conductivity and to
provide conducting paths in many electrical applications.
Electroplating with copper is employed in the manufacture of
electrical devices such as circuit boards, integrated circuits,
electrical contact surfaces and the like.
[0007] Plating metal is a complex process that involves multiple
ingredients in a plating bath. In addition to metal salts that
provide a source of metal, pH adjusters and surfactants or wetting
agents, many plating baths, such as electroplating baths, contain
chemical compounds that improve various aspects of the plating
process. Such chemical compounds or additives are auxiliary bath
components that are used to improve the brightness of the metal
plating, the physical properties of the plated metal especially
with respect to ductility and the micro-throwing power as well as
the macro-throwing power of the electroplating bath. Of main
concern are additives that have an effect on the bright finish,
leveling and uniformity of metal deposition on surfaces.
Maintaining bath concentrations of such additives within close
tolerances is important to obtain high quality metal deposits. Such
additives do breakdown during metal plating. The additives
breakdown due to oxidation at the anode, reduction at the cathode
and by chemical degradation. When additives breakdown during
plating, the breakdown products may result in metal layer deposit
characteristics that are less than satisfactory for industry
standards. Regular additions of additives based upon empirical
rules established by workers in the industry to try and maintain
optimum concentrations of the additives have been employed.
However, monitoring the concentrations of the additives that
improve metal plating is still very difficult because the additives
are present in small concentrations, i.e., parts per million of
solution, in the plating baths. Also the complex mixtures of the
additives and the degraded products formed from the additives
during plating complicate the replenishment process. Further,
depletion of specific additives is not always constant with time or
bath use. Accordingly, the concentration of the specific additives
is not accurately known and the level of the additives in the bath
eventually diminishes or increases to a level where the additives
are out of the acceptable range of tolerance. If the additive
content goes too far out of the range of tolerance, the quality of
the metal deposit suffers and the deposit may be dull in appearance
and/or brittle or powdery in structure. Other consequences include
low throwing power and/or plating folds with bad leveling.
Electroplating of through-hole interconnections in the manufacture
of multi-layer printed circuit boards is an example of where high
quality plating is required.
[0008] Stability and lifetime of a plating bath is very important.
Increased stability of the additives that improve metal plating
leads to longer lifetimes for plating baths. Plating baths having
longer lifetimes are economically very important. Frequent
replacement of plating baths, as mentioned above, as well as
disposal of baths containing degraded additives interrupts metal
plating operations. Such interruptions reduce product yield.
Accordingly, stable plating baths where breakdown of the additives
is prevented or reduced, are highly desirable.
[0009] U.S. Pat. No. 4,469,564 discloses a copper electroplating
process that allegedly increases the electroplating bath lifetime.
The patent states that the process may be employed with a soluble
or insoluble anode. A cation-permeable membrane surrounds the anode
to prevent organic additives from contacting the anode and being
oxidized by the anode. A disadvantage to such a process is that the
cation-permeable membranes are exposed to corrosive chemicals for
long periods of time that may cause the membranes to decompose. For
example, bath pH ranges may be less than 1.0 to as high as 11.0 and
higher. Also, bath pH ranges may fluctuate over time as bath
components are consumed or breakdown. Thus, workers in the art must
be selective in choosing a membrane with a chemical composition
that does not breakdown due to pH fluctuations during
electroplating. Additionally, as discussed above, electroplating
baths contain a variety of components. Components such as the
organic additives or their breakdown products may block pores in
the cation-permeable membrane preventing passage of cations through
the bath. Thus, workers must shut down the electroplating process
and replace the membrane. Both blockage of the pores and shutting
down the process lead to inefficiency in metal electroplating.
[0010] Japanese Patent Application 63014886 A2 discloses an acid
copper electroplating bath with chloride ions and also containing
transition metal ions in amounts of from 0.01-100 g/l. The
electroplating bath allegedly does not suffer from organic additive
consumption. Such organic additives include brighteners, leveling
agents, hardener, malleability and ductility modifiers, and
deposition modifiers.
[0011] EP 0402 896 discloses a method of stabilizing an organic
additive, such as a brightener, in an acid copper electroplating
solution. The process employs a soluble anode of copper chips in a
titanium basket. Transition metal salts of manganese, iron,
chromium, and titanium are added to the electroplating solution in
concentrations of not more than 5 g/l. The transition metals may
exist in at least two positive oxidation states, but are
substantially present in solution in their lowest common positive
oxidation state. The presence in solution of the positive oxidation
states of the transition metal ions allegedly stabilizes the
organic additives.
[0012] U.S. Pat. No. 6,099,711 discloses an electroplating process
employing an insoluble anode where metal ions, such as copper ions,
are replenished in the electroplating bath by employing a metal ion
generator in the form of a reversible redox system. Because an
insoluble anode is employed instead of a soluble anode, metal ions
are not replenished in the bath by dissolution of the anode. Thus,
the reversible redox system replenishes the metal ions. Iron (II)
and iron (III) compounds are used as an electrochemically
reversible redox system. Other redox systems disclosed in the
patent include metals of titanium, cerium, vanadium, manganese and
chrome. Such metals may be added to a copper depositing solution in
the form of iron (II) sulfate-heptahydrate, iron (II)
sulfate-nonahydrate, titanyl-sulfuric acid, cerium (IV) sulfate,
sodium metavanadate, manganese (II) sulfate or sodium chromate. The
patent states that the redox systems may be combined.
[0013] In addition to replenishing metal ions in the electroplating
bath, the patent states that the process prevents degradation of
organic additives to a significant extant. Degradation of large
amounts of organic additives in a bath occurs electrolytically at
the anode due to the anode potentials. Workers in the art believe
that the potential of the iron (II) to Iron (III) redox reaction
(about 0.530 V vs SCE) provides an anode potential low enough to
prevent brightener oxidation at the anode. Thus, brightener
consumption is reduced. Such organic additives include brighteners,
levelers, and wetting agents. Brighteners that are employed include
water-soluble sulfur compounds and oxygen-containing high-molecular
weight compounds. Other additive compounds include nitrogenous
sulfur compounds, polymeric nitrogen compounds and/or polymeric
phenazonium compounds.
[0014] Although the patent alleges to replenish metal ions and to
reduce brightener consumption, the process, disclosed in the '711
patent, has disadvantages. Iron (III) may be reduced back to iron
(II) in the reversible redox reaction instead of oxidizing copper
to copper (II). Additionally, there is the problem that iron may
build-up in the system over time requiring shut down and cleaning
operations. Such operations reduce the efficiency of the process,
and raise the cost of the process. Another disadvantage to the
process is that the concentrations of the compounds in the redox
system must be arranged in such a way that a constant concentration
of metal ions is maintained in the deposition solution. Thus, there
is a narrow or nonexistent margin of error in the concentrations of
redox compounds in the deposition solution for the process to
operate. Accordingly, minor changes in the concentrations of the
redox compounds may hinder the operation of the process.
[0015] Japanese Patent Application 96199385 discloses an
electroplating method and solution containing fluoride-based
surfactants and organic additives such as brighteners. Addition of
the fluoride-based surfactants allegedly prevents brightener
consumption.
[0016] Although there are methods for preventing the degradation of
additives in metal plating baths, there is still a need for
additional methods of preventing the degradation of bath
additives.
SUMMARY OF THE INVENTION
[0017] The present invention is directed to a metal plating bath
containing organic compounds that inhibit the degradation of
additives in the plating bath, and a method of plating a metal on a
substrate employing the metal plating baths. Such organic compounds
have the following formula: 1
[0018] where R, R.sup.1, R.sup.2, and R.sup.3 are each
independently selected from hydrogen; halogen; (C.sub.1-C.sub.20)
linear, branched, or cyclic alkyl; (C.sub.2-C.sub.20) linear,
branched, or cyclic alkenyl; (C.sub.2-C.sub.20) linear or branched
alkynyl; --CN; --SCN; --C.dbd.NS; --SH; --NO.sub.2; --SO.sub.2H;
--SO.sub.3M; --PO.sub.3M; --P(R.sup.4).sub.2, where R.sup.4 is
hydrogen or halogen; --Si(OH).sub.3; (C.sub.1-C.sub.20)
alkyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, (C.sub.1-C.sub.12)
alkyphenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
-phenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, where x is an integer of
from 1-500 and R.sup.6 is hydrogen, (C.sub.1-C.sub.4) alkyl or
phenyl; silane; silyl; sulfonyl halide; aminyl; hydroxyaminyl;
aminyl halide; acyl halide; --COR.sup.5, where R.sup.5 is --OH, or
(C.sub.1-C.sub.20) linear, branched or cyclic alky,
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl,
(C.sub.2-C.sub.20) linear or branched alkynyl, or
(C.sub.1-C.sub.20) linear, or branched alkoxy; or --OH with the
proviso that a carboxy is present as a substituent on the compound;
the (C.sub.1-C.sub.20) alky, (C.sub.2-C.sub.20) alkenyl, the
(C.sub.2-C.sub.20) alkynyl, and the (C.sub.1-C.sub.20) alkoxy
groups may be unsubstituted or substituted; M is hydrogen or an
alkali metal; or
[0019] R.sup.1 and R.sup.2 may be taken together to form a chemical
bond; or R.sup.1 and R.sup.2 may be taken together along with the
atoms to which they are attached to form a 5 to 7 membered ring, or
to form a 5 to 7 membered heterocyclic ring where oxygen or
nitrogen are hetero-atoms in the ring, the 5 to 7 membered ring, or
the 5 to 7 membered heterocyclic ring may contain one or more
carbonyl groups; the 5 to 7 membered ring or the 5 to 7 membered
heterocyclic ring may be fused with one or more five to six
membered rings, the one or more five to six membered fused rings
may contain one or more hetero-atoms where the hetero-atom is
oxygen or nitrogen, the 5 to 6 membered fused rings and the 5 to 6
membered fused rings with a heteroatom may contain a carbonyl
group; and the 5 to 7 membered rings, the 5 to 6 membered fused
rings, and the heterocyclic rings may be unsubstituted or
substituted.
[0020] The additive consumption inhibiting organic compounds of the
present invention may be employed in metal plating baths for
plating copper, gold, silver, palladium, platinum, cobalt, cadmium,
chromium, bismuth, indium, iridium, ruthenium, and rhodium.
[0021] Advantageously, addition of the organic compounds of the
present invention that inhibit additive consumption to a plating
bath provide for a plating bath that has a long life, and a method
of metal plating that is very efficient. Also, because the organic
compounds of the present invention inhibit degradation of the
additives, plating baths of the present invention provide for
uniform, high brightness metal layers with good physical-mechanical
characteristics on substrates.
[0022] Metal plating baths of the present invention may be employed
to plate metal layers on any substrate that may be metal plated.
Metal plating methods of the present invention involve passing a
current between two electrodes, a cathode and an anode, immersed in
a bath containing dissolved plating metal, bath additives and one
or more additive consumption inhibiting organic compounds of the
present invention. Current is passed through the bath until a
substrate is plated with a desired thickness of metal.
[0023] The additive consumption inhibiting organic compounds and
methods of the present invention may be employed in any industry
where metal plating is used. For example, the metal plating baths
may be employed in the manufacture of electrical devices such as
printed circuit and wiring boards, integrated circuits, electrical
contact surfaces and connectors, electrolytic foil, silicon wafers
for microchip applications, semi-conductors and semi-conductor
packaging, lead frames, optoelectronics and optoelectronics
packaging, solder bumps such as on wafers, and the like. Also, the
metal plating baths may be employed for metal plating decorative
articles for jewelry, furniture fittings, automobile parts,
sanitary appliances, and the like. Further, organic compounds of
the present invention may be employed in waste treatment
methods.
[0024] The present invention also includes an apparatus composed of
an electrical power source, an anode, a cathode, and a metal
plating bath containing the additive consumption inhibiting organic
compounds of the present invention. The cathode of the apparatus is
the article that is to be metal plated. The apparatus may be a
vertical or a horizontal metal plating apparatus.
[0025] A primary objective of the present invention is to provide
organic compounds that inhibit degradation of additives in a metal
plating bath.
[0026] Another objective of the present invention is to provide a
metal plating bath that has a long life.
[0027] An additional objective of the present invention is to
provide for an efficient method for plating a metal on a
substrate.
[0028] A further objective of the present invention is to provide a
method for plating a uniform, high brightness metal layer with good
physical-mechanical properties on a substrate.
[0029] Still yet, an additional objective of the present invention
is to provide an apparatus containing a metal plating bath with an
organic compound that inhibits additive consumption.
[0030] Additional objectives and advantages may be ascertained by a
person of skill in the art after reading the detailed description
of the invention and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagrammatic illustration for treating a
workpiece by a vertical method in accordance with the present
invention; and
[0032] FIG. 2 is a diagrammatic illustration of an apparatus for
treating a workpiece by a horizontal method in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Metal plating baths of the present invention contain organic
compounds that inhibit the degradation of additives added to metal
plating baths to improve metal deposition on a substrate. Such
organic compounds include organic compounds having the following
formula: 2
[0034] where R, R.sup.1, R.sup.2, and R.sup.3 are each
independently selected from hydrogen; halogen; (C.sub.1-C.sub.20)
linear, branched, or cyclic alkyl; (C.sub.2-C.sub.20) linear,
branched, or cyclic alkenyl; (C.sub.2-C.sub.20) linear, or branched
alkynyl; sulfonyl halide; --CN; --SCN; --C.dbd.NS; --SH;
--NO.sub.2; --SO.sub.2H; --SO.sub.3M; --PO.sub.3M;
--P(R.sup.4).sub.2, where R.sup.4 is hydrogen or halogen;
(C.sub.1-C.sub.20) alkyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6,
(C.sub.1-C.sub.12)alkylphenyl-O(C.sub.2-C.sub.3O).sub.xR.sub.6, or
phenyl-O(C.sub.2-C.sub.3O).sub.xR.sup.6, where x is an integer of
from 1-500 and R.sup.6 is hydrogen, (C.sub.1-C.sub.4) alkyl or
phenyl; silyl; silane; --Si(OH).sub.3; aminyl; aminyl halide;
hydroxyaminyl; acyl halide; --COR.sup.5, where R.sup.5 is --OH, or
(C.sub.1-C.sub.20) linear, branched or cyclic alkyl,
(C.sub.2-C.sub.20) linear, branched, or cyclic alkenyl,
(C.sub.2-C.sub.20) linear, or branched alkynyl, (C.sub.1-C.sub.20)
linear, or branched alkoxy; or R, R.sup.1, R.sup.2, and R.sup.3 are
each independently --OH with the proviso that when hydroxyl is a
substituent the compound also has a carboxyl group; the
(C.sub.1-C.sub.20) alkyl, the (C.sub.2-C.sub.20) alkenyl, the
(C.sub.2-C.sub.20) alkynyl, and the (C.sub.1-C.sub.20) alkoxy
groups may be unsubstituted or substituted; M is hydrogen or an
alkali metal such as Li, Na, K, Rb, or Cs. Halogens include F, Cl,
Br, or I.
[0035] R.sup.1 and R.sup.2 may be taken together to form a
carbon-carbon bond; or R.sup.1 and R.sup.2 may be taken together to
form a 5 to 7 membered carbocyclic ring, or a 5 to 7 membered
carbocyclic ring fused with one or more five or six membered rings.
The 5 to 7 membered carbocyclic ring and the one or more five or
six membered fused rings may each contain one or more carbonyls in
the ring. The 5 to 7 membered rings and the five or six membered
fused rings may each optionally contain a hetero-atom such as
oxygen or nitrogen to form one or more heterocyclic rings. The
heterocyclic rings may contain a carbonyl in the ring. The 5 to 7
membered rings, the five to six membered fused rings, and the
heterocyclic rings may be unsubstituted or substituted.
[0036] The (C.sub.1-C.sub.20) alkyl, the (C.sub.2-C.sub.20)
alkenyl, the (C.sub.2-C.sub.20) alkynyl, the (C.sub.1-C.sub.20)
alkoxy, the 5 to 7 membered rings, the 5 to 6 membered fused rings
and the heterocyclic rings may be substituted with one or more
substituents which include, but are not limited to, halogen,
--Si(OH).sub.3, silane, silyl, aryl, alkoxy, --SO.sub.3M,
--PO.sub.3M, sulfonyl halide, --SO.sub.2H, --NO.sub.2, --CN, --SCN,
--C.dbd.NS, --P(R.sup.4).sub.2, ester containing group, --SH,
aminyl, aminyl halide, hydroxyaminyl, acyl halide, carboxyl, keto,
or --OH. A hydroxyl group is included as a substituent on an
additive consumption inhibiting compound of the present invention
with the proviso that the additive consumption inhibiting compound
also has at least one carboxyl group. R.sup.4 and M are as defined
above. The cyclic alkenyl groups and the aryl radical include, but
are not limited to, phenyl, naphthyl, anthryl, phenanthryl,
furanyl, pyridinyl, and pyrimidinyl radicals. Substitution within
the scope of the present invention means that a hydrogen is
replaced with a substituent such as the substituent groups
mentioned above.
[0037] The organic additive consumption inhibiting compounds of the
present invention also include salts, hydrates and acid anhydrides
of the foregoing compounds. Such salts include, but are not limited
to, alkali metal salts of acids.
[0038] Preferred compounds of the present invention are aromatic
compounds as well as compounds with triple bonds. Such compounds
are where at least one of R, R.sup.1, R.sup.2, or R.sup.3 is
(C.sub.5-C.sub.20) cyclic alkenyl, or where R.sup.1 and R.sup.2 are
taken together to form a bond, or where R.sup.1 and R.sup.2 are
taken together to form a 5 to 7 membered ring, a 5 to 7 membered
ring fused with one or more 5 or 6 membered ring, or a 5 to 7
membered heterocyclic ring fused with one or more 5 to 6 membered
ring, or a 5 to 7 membered heterocyclic ring fused with one or more
5 to 6 membered heterocyclic ring. The foregoing rings are
sufficiently unsaturated to form one or more aromatic ring and may
be unsubstituted or substituted with the substituent groups recited
above. Especially preferred compounds for practicing the present
invention are aromatic compounds with at least one carboxyl
substituent. Most preferred compounds for practicing the present
invention are unsaturated compounds with at least one carboxyl
group and at least one hydroxyl group, especially aromatic
compounds.
[0039] Examples of especially preferred acids, salts of acids and
hydrates thereof include 2,6-dihydroxybenzoic acid,
4-hydroxybenzoic acid resorcinol, 2,3-dihydroxybenzoic acid,
2,4-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid,
2,3,4-trihydroxybenzoic acid, methyl-3,4,5-trihydroxybenzoate,
methyl-2,4-dihydroxybenzoate, and 4-hydroxymandelic acid
monohydrate.
[0040] Examples of other suitable acids and anhydrides include
3-(phenylthio)acetic acid, 4-hydroxybenzene sulfonic acid, gallic
acid, 4-vinylbenzoic acid, 3,4-dihydroxy cinnamic acid, 4-methoxy
cinnamic acid, 2-hydroxy cinnamic acid, phthalic acid,
trans-3-furanyl acrylic acid, vinyl acetic acid, and sulfanilic
acid. Also included are acid anhydrides such as phthalic
anhydride.
[0041] Examples of other suitable organic compounds within the
scope of the present invention include aromatic hydrocarbons,
unsubstituted or substituted, such as phenyl methyl and the
like.
[0042] The additive consumption inhibiting organic compounds may be
employed in metal plating baths for plating copper, gold, silver,
palladium, platinum, cobalt, chromium, cadmium, bismuth, indium,
rhodium, iridium, and ruthenium. Preferably, the foregoing
compounds may be employed in metal plating baths for plating metals
selected from the group consisting of copper, gold, silver,
platinum, palladium, iridium, and ruthenium. More preferably the
foregoing additive consumption inhibiting compounds are employed in
baths for plating metals selected from copper, iridium, or
ruthenium. Most preferably, the foregoing additive consumption
inhibiting compounds are employed in plating baths for plating
copper.
[0043] Adding one or more of the additive consumption inhibiting
organic compounds of the present invention to metal plating baths
prevent or reduce the degradation of additives in the metal plating
baths. Preferably, the metal plating baths are electroplating
baths. Preferably the metal plating baths of the present invention
are aqueous. The additive consumption inhibiting organic compounds
are added in amounts of generally from about 0.001 g/L to about 100
g/L of bath. Preferably, the organic compounds are generally
employed in plating baths of from about 0.01 g/L to about 20.0
g/L.
[0044] The additive consumption inhibiting organic compounds may be
added to plating baths by any suitable method employed to add
components to a bath. One method is to mix the organic compounds
into the plating bath with the other bath components and
additives.
[0045] Additives that the organic compounds inhibit degradation of
include, but are not limited to, brighteners, levelers, hardeners,
wetting agents, malleability, ductility and deposition modifiers,
suppressants and the like. Such additives are predominantly organic
compounds. The additive consumption inhibiting organic compounds
are especially effective in inhibiting consumption of brighteners
and levelers. Additives as defined within the scope of the present
invention include any compound, salt or liquid that may be added to
a metal plating bath with the exception of a consumption inhibiting
organic compounds of the present invention.
[0046] While not being bound to any theory, the additive
consumption inhibiting organic compounds of the present invention
are believed to inhibit additive consumption by one or a
combination of the following mechanisms. Many additives break down
or decompose at the anode to oxidation products. The organic
compounds of the present invention may competitively adsorb onto an
anode over additives, and become oxidized in place of the
additives. Many metal plating baths contain chloride. Chloride is
often added to metal plating baths in the form of HCl. Chloride is
oxidized at the anode to chlorine. Chlorine may then oxidize the
bath additives reducing the effectiveness of the additives in the
metal plating bath. By adding one or more of the additive
consumption inhibiting compounds to the metal plating bath,
chlorine oxidizes the one or more organic compounds over the
additives. In other words, the additive consumption inhibiting
organic compounds may perform as sacrificial species. In another
proposed mechanism, the additive consumption inhibiting organic
compounds compete with chloride, or with both chloride and the
additives at the anode surface. Thus, the additive consumption
inhibiting organic compounds are oxidized at the anode over the
chloride, or both the chloride and the additives.
[0047] Examples of suitable brighteners employed in plating baths
of the present invention, include but are not limited to, compounds
that contain structural formulas: HO.sub.3S--R.sup.11--SH,
HO.sub.3S--R.sup.11--S--S--- R.sup.11--SO.sub.3H, where R.sup.11 is
C.sub.1-C.sub.6 or an aryl group, and
HO.sub.3S--Ar--S--S--Ar--SO.sub.3H, where Ar is phenyl or naphthyl.
Substituents of the alkyl and aryl groups may be, for example,
alkyl, halo and alkoxy. Examples of such brightening agents are
3-mercapto-propylsulfonic acid (sodium salt),
2-mercapto-ethanesulfonic acid (sodium salt), and bissulfopropyl
disulfide (BSDS). Such compounds are disclosed in U.S. Pat. Nos.
3,770,598, 4,374,709, 4,376,685, 4,555,315 and 4,673,469, all
incorporated herein in their entirety by reference. Such
polysulfides also may be employed to increase ductility of
deposited metal.
[0048] Examples of levelers that may be employed in a plating bath
include, but are not limited to, alkylated polyalkyleneimines and
organic sulfo sulfonates. Examples of such compounds include
1-(2-hydroxyethyl)-2-imidazolidinethione (HIT), 4-mercaptopyridine,
2-mercaptothiazoline, ethylene thiourea, thiourea and alkylated
polyalkyleneimine. Such compounds are disclosed in U.S. Pat. Nos.
4,376,685, 4,555,315, and 3,770,598, the disclosures of which are
hereby incorporated herein in their entireties by reference.
[0049] Examples of other additives that may function as brighteners
in plating baths within the scope of the present invention include,
but are not limited to, sulfur compounds such as
3-(benzthiazoyl-2-thio)-propylsu- lfonic acid sodium salt,
3-mercaptopropane-1-sulfonic acid sodium salt,
ethylenedithiodipropylsulfonic acid sodium salt,
bis-(p-sulfophenyl)-disu- lfide disodium salt,
bis-(.omega.-sulfobutyl)-disulfide disodium salt,
bis-(.omega.-sulfohydroxypropyl)-disulfide disodium salt,
bis-(.omega.-sulfopropyl)-disulfide disodium salt,
bis-(.omega.-sulfopropyl)-sulfide disodium salt,
methyl-(.omega.-sulfopro- pyl)-disulfide sodium salt,
methyl-(.omega.-sulfopropyl)-trisulfide disodium salt,
O-ethyl-dithiocarbonic acid-S-(.omega.-sulfopropyl)-ester,
potassium salt thioglycoli acid, thiophosphoric
acid-O-ethyl-bis-(.omega.- -sulfpropyl)-ester disodium salt,
thiophosphoric acid-tris(.omega.-sulfopr- opyl)-ester trisodium
salt, N,N-dimethyldithiocarbamic acid (3-sulfopropyl) ester, sodium
salt (DPS), (O-ethyldithiocarbonato)-S-(3-s- ulfopropyl)-ester,
potassium salt (OPX), 3-[(amino-iminomethyl)-thio]-1-pr-
opanesulfonic acid (UPS), 3-(2-benzthiazolylthio)-1-propanesulfonic
acid, sodium salt (ZPS), thiol of bissulfopropyl disulfide (MPS)
and the like.
[0050] Examples of oxygen containing high molecular weight
compounds that may be employed as suppressors include
carboxymethylcellulose, nonylphenolpolyglycol ether,
octandiolbis-(polyalkylene glycolether), octanolpolyalkylene
glycolether, oleic acidpolyglycol ester, polyethylenepropylene
glycol, polyethylene glycol, polyethylene glycoldimethylether,
polyoxypropylene glycol, polypropylene glycol, polyvinylalcohol,
stearic acidpolyglycol ester, stearyl alcoholpolyglycol ether, and
the like.
[0051] Aromatic and aliphatic quaternary amines also may be added
to plating baths to improve deposit brightness. Dyes of the
phenazine class (Safranine type) and phenazine azo dyes (Janus
Green B type) may be employed as levelers. Polyethers are used to
improve thickness and uniformity of metal plating.
[0052] Brighteners and levelers are added to plating baths in
amounts of from about 1 part per billion to about 1 g/L of bath.
More often, brighteners and levelers range from about 10 parts per
billion to about 500 parts per million. Ranges for bath components
may vary from one bath composition to the next. Thus, the foregoing
weight ranges for the additives are general ranges.
[0053] Examples of suitable wetting agents or surfactants that may
be employed in plating baths of the present invention include
nonionic surfactants such as alkyl phenoxy polyethoxyethanols.
Other suitable wetting agents containing multiple oxyethylene
groups also may be employed. Such wetting agents include compounds
of polyoxyethylene polymers having from as many as 20 to 150
repeating units. Such compounds also may perform as suppressors.
Also included in the class of polymers are block copolymers of
polyoxyethylene and polyoxypropylene. Surfactants and wetting
agents are added in conventional amounts.
[0054] In addition to the additives, other plating bath components
are included in plating baths as a source of metal ions, pH
adjusters, such as inorganic acids, and a source of halide ions.
Generally, plating baths are aqueous. The pH range of the baths may
range from 0 to about 14, preferably from 0 to about 8. Wetting
agents employed in plating baths and amounts employed in such baths
are well known in the art. Inorganic acids employed include, but
are not limited to, sulfuric acid, hydrochloric acid, nitric acid,
phosphoric acid and the like. Sulfuric acid is a preferred acid.
Halogen ions are optional. Halogen ions employed in plating baths
preferably include chloride, fluoride, and bromide. Such halides
are added into the bath as a water soluble salt. Chloride is
preferred, and is introduced into the bath, preferably, as HCl.
Water soluble salts of metals provide a source of the metal to be
plated on a substrate. Such water soluble salts include metal salts
of copper, chromium, gold, silver, cadmium, platinum, palladium,
cobalt, bismuth, indium, rhodium, ruthenium, and iridium.
[0055] The most preferred selected metal to be plated with the
baths of the present invention consists of copper. Preferably, the
copper is electroplated. Copper that is useful may be in the form
of any solution soluble copper compound. Suitable copper compounds
include, but are not limited to, copper halides, copper sulfates,
copper alkane sulfonate, copper alkanol sulfonate, and the like.
When copper halide is used, chloride is the preferred halide.
Preferred copper compounds are copper sulfate, copper alkane
sulfonate, or mixtures thereof. The more preferred are copper
sulfate, copper methane sulfonate or mixtures thereof. Copper
compounds useful in the present invention are generally
commercially available or may be prepared by methods known in the
literature. When copper is plated on a substrate the pH of the bath
may range from 0 to about 14.0. Preferably the bath ranges from a
pH of from 0 to about 8.0.
[0056] Metal ions range in concentration in the plating baths of
from about 0.010 g/L to about 200 g/L, preferably from about 0.5
g/L to about 100.0 g/L. When copper is employed the amount of
copper may range from about 0.01 to about 100 g/L. Preferably,
copper ranges from about 0.10 g/L to about 50 g/L. When the bath of
the present invention is used in a non-high speed plating process,
the amount of copper present in the bath ranges from about 0.02 g/L
to about 25 g/L. When the bath of the present invention is used in
a high speed plating process, the amount of copper present in the
bath ranges from about 1.0 g/L to about 100 g/L, preferably from
about 2.0 g/L to about 50 g/L.
[0057] Halide ions range in concentration of from 0 mg/L to about 1
g/L, preferably from about 1.0 mg/L to about 150 mg/L. Acids are
added to the plating baths to obtain a pH range of from about 0 to
about 8.0. Accordingly, acids are added in amounts of from about 10
g/L to about 600 g/L, preferably from about 15 g/L to about 500
g/L.
[0058] An example of an acid copper electroplating bath for
practicing the present invention has a composition as follows:
1 Copper Ions (as Copper Sulfate) 0.01 to 50 g/L Sulfuric Acid
(Concentrated) 15 to 500 g/L Chloride Ions (as Sodium Chloride) 1
ppm to 150 ppm Additives As Required Additive Preserving Compound
0.1 to 10 g/L Water To 1 liter
[0059] While the organic compounds of the present invention may be
employed to prevent degradation of additives in any suitable
plating bath where a substrate is to be metal plated, preferably,
the additive consumption inhibiting compounds are employed in
electroplating baths. Such electroplating baths are employed in
electrodeposition of a metal on a substrate such as in the
manufacture of printed wiring boards and silicon wafers used in
microchip applications, and in the manufacture of other components
for electrical devices. Electroplating processes involve passing
current through an anode, an electroplating solution, and a cathode
for a sufficient amount of time to metal plate a substrate to a
desired thickness. The anode may be a soluble anode (composed of a
metal such as copper that dissolves and replenishes the
electroplating bath as plating occurs). Alternatively, an insoluble
anode (composed of an inert material such as platinum, platinized
titanium, lead, and the like) may be employed where electroplating
rates are greater than in methods using soluble anodes. Preferably,
the present invention is employed in plating processes employing an
insoluble anode where problems associated with additive consumption
(often oxidation at the anode) are greater than with processes
employing soluble anodes.
[0060] Examples of useful insoluble anodes are anodes that have
surfaces with oxides of iridium and tantalum. Such anodes have from
about 20 to about 90 moles percent of iridium with the remainder
tantalum. Preferred is about 60 to about 90 mole percent of iridium
with the remainder tantalum. The anodes are made by coating iridium
and tantalum on a conducting substrate such as a titanium
substrate.
[0061] Other suitable anodes include anodes composed of at least
about 10 mole percent of group VIII metals, at least about 10 mole
percent valve metal and at least about 5 mole percent binder metal.
Group VIII metals include cobalt, nickel, ruthenium, rhodium,
palladium, iridium and platinum. Valve metals include titanium,
zirconium, hafnium, vanadium, niobium and tantalum. Binder metals
include beryllium, calcium, strontium, barium, scandium, yttrium,
lanthanum and rare earth elements with atomic numbers 58 through
71. Especially useful is an oxide composition with from about 5 to
about 20 mole percent of barium, and the ratio of iridium to
tantalum between about 1/4 and about 4. Such a composition is about
5 mole percent barium, from about 30 to about 40 mole percent
iridium with the remainder tantalum. Additionally, osmium, silver
and gold or their oxides may be employed in insoluble anodes.
[0062] As mentioned above, plating baths of the present invention
may be employed in any suitable plating process where metal is
plated on a substrate. Plating baths of the present invention are
especially suitable for plating substrates in the manufacture of
electronic devices such as in the printed wiring board industry and
the manufacture of silicon wafers in microprocessing.
[0063] In an electroplating process, the substrate to be plated is
used as a cathode. A soluble or preferably an insoluble anode, as
described above, is employed as a second electrode. A process of
pulse plating, direct current (DC) plating, or a combination of DC
and pulse plating may be employed. Such plating methods are known
in the art. Current densities and electrode surface potentials may
vary depending on the specific substrate to be plated. Generally,
anode and cathode current densities may vary from about 1 to about
1000 amps/ft.sup.2 (ASF). Plating baths are maintained in a
temperature range of from about 20.degree. C. to about 110.degree.
C. Temperature ranges for specific metals vary. Copper baths are
maintained in a temperature range of from about 20.degree. C. to
about 80.degree. C. with acid copper baths at temperatures of from
about 20.degree. C. to about 50.degree. C. Plating is continued for
a time sufficient to form a deposit of desired thickness.
Generally, plating time for a circuit board is from about 45
minutes to about 8 hours. For circuit board manufacture, a desired
thickness may range from about 0.5 to about 3.0 mils. More often
layer thickness ranges from about 1.0 to about 1.5 mils.
[0064] Both vertical and horizontal plating processes may be
employed. In the vertical process, the substrate, such as a printed
circuit or wiring board, is sunk in a vertical position into a
container containing a plating bath solution of the present
invention. The substrate, which functions as a cathode, is situated
in the vertical position opposite at least one anode, preferably an
insoluble anode. The substrate and the anode are connected to a
current source. Instead of regulating the current with the current
source, there also can be a voltage arrangement where the voltage
between the substrate and the anode is regulated. Plating solution
is directed continuously through the container by means of
transporting equipment such as a pump.
[0065] An example of an arrangement that is suitable for treating a
substrate or workpiece by a vertical method and apparatus is
represented in FIG. 1. Apparatus 10 is composed of container 12
with metal plating bath 14 that contains an additive consumption
inhibiting organic compound or the present invention. The metal
plating bath 14 may be used, for example, for copper plating and
contains previously mentioned components and additives.
[0066] Workpiece 16 (cathode), for example a circuit board, and
anodes 18, for example insoluble titanium anodes coated with
iridium dioxide, are immersed into metal plating bath 14. Workpiece
16 and anodes 18 are connected electrically to current source 20.
Instead of regulating the current with the current source, a
voltage arrangement (not shown) may be used to regulate voltage
between the workpiece 16 and anodes 18. Metal plating bath 14 is
directed continuously to second container or reservoir 22 by a
transporting means (not shown) such as a pump. Reservoir 22, which
metal plating bath 14 flows through, replenishes metal bath
components and additives in metal plating bath 14 such as copper
salts, brighteners, levelers, additive consumption inhibiting
organic compounds and the like.
[0067] In the horizontal plating process, the substrate is
transported through a conveyorized unit in a horizontal position
with a horizontal direction of movement. Plating bath is injected
continuously from below and/or from above onto the substrate by
means of splash nozzles or flood pipes. The anodes are arranged at
a spacing relative to the substrate and are brought into contact
with the plating bath by means of a suitable device. The substrate
is transported by means of rollers or plates.
[0068] An example of a horizontal method and apparatus that may be
employed to practice the present invention is illustrated in FIG.
2. Spray chamber 24 of apparatus 46 is formed with slots 26 at
either end to allow for continuous conveyance of panel 28, such as
a circuit board panel to be metal plated, to enter and leave
chamber 24. While a circuit board panel is illustrated, any
suitable surface that may be plated by a horizontal apparatus lies
within the scope of the present invention. Panel 28 is supported
for moving in the direction of the arrow by idler rollers 30. A
series of roller brushes 32 is positioned to contact both upper and
lower surfaces of panel 28 with a series of anodes 34 positioned to
contact roller brushes 32 on the sides of idler rollers 30 away
from panel 28. Anodes 34 are formed of any suitable metal such as
titanium coated with iridium dioxide. While any suitable anode may
be employed, an insoluble anode such as the titanium coated iridium
dioxide anode is preferred. Anodes 34 are positioned such that the
anodes touch the upper set of idler rollers 30 from above, and
touch the lower set of idler rollers 30 from below. Anodes 34 are
electrically connected in parallel to a positive terminal of power
supply 36. A negative terminal of power supply 36 is connected to
panel 28 (cathode) that is to be plated. Spray jets 38 which are
connected to reservoir 42 containing metal plating bath 40 by means
of lines 44 are arranged to spray metal plating bath 40 down on
both anodes 34 and roller brushes 32 as well as panel 28 between
roller brushes 32. Arrows show the path for the metal bath flow
through lines 44. Metal plating bath 40 is pumped from reservoir 42
through lines 44 by a pumping means (not shown) in mechanical
connection to reservoir 42. The transport mechanism means (not
shown) for panel 28 is a conveyor-type mechanism that provides for
a continuous movement of panel 28 through chamber 24 while
maintaining electrical contact between the negative pole of power
supply 36 and panel 28.
[0069] By preventing or substantially reducing the amount of
additive breakdown, the additive consumption inhibiting organic
compounds provide for improved brightness of plated metal and
improved physical-mechanical properties of the plated metal. Metal
layers plated with baths of the present invention are not brittle
or powdery in structure. Also, metal layers plated with the baths
of the present invention have good throwing power and no plating
folds. Such properties for metal layers are especially desirable
for through-holes in printed circuit and wiring boards.
Additionally, because the compounds prevent or substantially reduce
the amount of additives degraded during metal plating,
replenishment of the organic additives is reduced in contrast to
baths without the additive consumption inhibiting organic
compounds. Also, prevention of additive breakdown permits metal
plating operations to continue for longer periods without bath
replacement. Further, because the organic compounds of the present
invention inhibit degradation of additives, costly semi-permeable
membranes can be eliminated from apparatus during plating. Thus,
plating baths containing the additive consumption inhibiting
compounds provide for a more efficient and economic method for
metal plating than baths without the additive consumption
inhibiting organic compounds. Accordingly, metal plating baths of
the present invention provide for an improved metal plating
process. All numerical ranges in the present application are
inclusive and combinable.
[0070] While the present invention is described with an emphasis on
electroplating processes in the printed wiring board industry, the
present invention may be employed in any suitable plating process.
The compounds may be employed in metal plating baths in the
manufacture of electrical devices such as printed circuit and
wiring boards, integrated circuits, electrical contact surfaces and
connectors, electrolytic foil, silicon wafers for microchip
applications, semi-conductors and semi-conductor packaging, lead
frames, optoelectronics and optoelectronic packaging, solder bumps
such as on wafers, and the like. Additionally, the metal plating
baths may be employed for metal plating decorative articles for
jewelry, furniture fittings, automobile parts, sanitary appliances,
and the like. Further, the additive consumption inhibiting
compounds of the present invention may be employed in waste
treatment methods.
[0071] The following examples are provided to better describe the
present invention, and are not intended to limit the scope of the
invention.
Example 1
[0072] Compounds within the scope of the present invention were
tested for their ability to prevent brightener consumption in a
copper plating bath. Hydrodynamically controlled Hull Cells were
used to measure the ability of a compound to prevent brightener
consumption. A compound's ability to prevent brightener consumption
was measured by recording the number of fully bright cathodes
produced in the about 5-90 ASF current density range without
replenishing the brightener.
[0073] The copper plating bath employed in the tests was as
follows:
2 Bath Component Amount Copper Sulfate Pentahydrate 80 g/L Sulfuric
Acid (Concentrated) 225 g/L Chloride (as sodium chloride) 50 ppm
Polyethylene Oxide (suppressor) 1 g/L Bissulfopropyl Disulfide
(brightener) 1 ppm Water To 1 L
[0074] Compounds tested are disclosed in the table below along with
the results. Each compound was added to the plating baths in an
amount of about 1 g/L. A control bath with no brightener protecting
additives was also tested. Each Hull Cell experiment was performed
with copper clad FR4/glass-epoxy functioning as the cathode, and
iridium dioxide coated titanium mesh functioning as the anode
(insoluble anode). The cathode was electroplated at about 3 amps
for about 10 minutes with a DC rectifier. After about 10 minutes,
if the cathode deposit was bright in the about 5-90 ASF current
density range, then a new copper cathode was immersed and
electroplated. The process was repeated until the cathode deposit
was matte in the about 5-90 ASF current density range. About 7 g of
copper sulfate heptahydrate was added about every 30 minutes to the
plating baths to replenish copper ions. When a matte deposit was
recorded, the brightener was depleted from the bath.
[0075] The plating bath control without any brightener protecting
additives produced zero bright cathodes in the about 5-90 ASF
current density range. The number of consecutive bright cathodes
produced from a number of different brightener protecting compounds
is listed in the following table:
3 Compound Number of Bright Hull Cells 2,4,6-trihydroxybenzoic acid
7 2,4-dihydroxybenzoic acid 6 2,3-dihydroxybenzoic acid 3
4-hydroxybenzoic acid 3 2,6-dihydroxybenzoic acid 3 Vinyl acetic
acid 3 Control (no compound added) Less than 1
[0076] Best results were obtained with the aromatic acid with
hydroxyl substitution at the 2, 4 and 6 carbons and at the 2 and 4
carbons. All the compounds tested showed some brightener
consumption inhibition in contrast with the control that was
composed of only the copper bath components. Thus, the compounds
listed above may be added to a copper plating bath to inhibit
brightener consumption.
Example 2
[0077] Compounds within the scope of the present invention were
tested for their ability to prevent brightener consumption in a
copper plating bath. Hydrodynamically controlled Hull Cells were
used to measure the ability of a compound to prevent brightener
consumption. A compound's ability to prevent brightener consumption
was measured by recording the number of fully bright cathodes
produced in an about 5-90 ASF current density range without
replenishing the brightener.
[0078] The copper plating bath employed in the tests was as
follows:
4 Bath Component Amount Copper Sulfate Pentahydrate 80 g/L Sulfuric
Acid (Concentrated) 225 g/L Chloride (as sodium chloride) 50 ppm
Polyethylene Oxide (suppressor) 1 g/L Bissulfopropyl Disulfide
(brightener) 1 ppm Water To 1 L
[0079] Compounds tested are disclosed in the table below along with
the results. Each compound was added to the plating baths in an
amount of about 0.1 g/L. A control bath with no brightener
protecting additives was also tested. Each Hull Cell experiment was
performed with copper clad FR4/glass-epoxy functioning as the
cathode, and iridium dioxide coated titanium mesh functioning as
the anode (insoluble anode). The cathode was electroplated at about
3 amps for about 10 minutes with a DC rectifier. After about 10
minutes, if the cathode deposit was bright in the about 5-90 ASF
current density range, then a new copper cathode was immersed and
electroplated. The process was repeated until the cathode deposit
was matte in the about 5-90 ASF current density range, up to a
total of about thirty minutes of plating time, i.e., three
consecutive bright Hull Cell panels. When a matte deposit was
recorded, the brightener was depleted from the bath.
[0080] The plating bath control without any brightener protecting
additives produced zero bright cathodes in the about 5-90 ASF
current density range. The number of consecutive bright cathodes
produced from a number of different brightener protecting compounds
is listed in the following table:
5 Compound Number of Bright Hull Cells 2,4,6-trihydroxybenzoic acid
monohydrate 3 2,3-dihydroxybenzoic acid 3 4-hydroxybenzoic acid 3
2,4-dihydroxybenzoic acid 3 2,6-dihydroxybenzoic acid 3
2,3,4-trihydroxybenzoic acid 3 Hexadienoic acid 1 Trans-1-pentanoic
acid 1 4-vinylbenzoic acid 1 Control (free of consumption
inhibiting Less than 1 compound)
[0081] All of the compounds that were tested showed some brightener
consumption inhibition in contrast to the control bath that was
composed of only the copper bath components. However, best results
were obtained from compounds that were aromatic and contained
carboxyl and hydroxyl substituents. Such compounds produced 3
bright Hull Cells. In contrast, compounds that did not have at
least one hydroxyl group and a carboxyl group produced only 1
bright Hull Cell.
Example 3
[0082] The following comparative tests showed that the brightener
consumption inhibiting compounds of the present invention are an
improvement over iron redox methods for inhibiting brightener
consumption.
[0083] Four metal plating baths were prepared all composed of about
80 g/L of copper sulfate pentahydrate, about 225 g/L of sulfuric
acid, about 1 g/L of polyeththylene oxide and about 1 ppm of
bissulfopropyl disulfide (brightener). Iron (II) sulfate
heptahydrate was added to three of the four baths in different
quantities. One bath contained iron (II) sulfate heptahydrate in an
amount of about 1 g/L, the second bath contained about 10 g/L of
iron (II) sulfate heptahydrate and the third bath contained about
200 g/L of iron (II) sulfate heptahydrate. The iron (II) sulfate
heptahydrate was added to each of the baths to test the iron (II)
sulfate heptahydrate's ability to prevent brightener consumption
during plating copper onto copper clad FR4/glass-epoxy panels in a
standard Hull Cell. The fourth bath was a control bath. The Hull
Cell contained an iridium dioxide (IrO.sub.2) mesh-type insoluble
anode. The copper clad FR4/glass-epoxy panel functioned as the
cathode. Each Hull Cell was operated at about 3 amps for about 10
minutes.
[0084] After about 10 minutes of electroplating in the presence of
varying degrees of iron (II) sulfate, no fully bright panels were
produced with a current density of about 5-90 ASF. Thus,
significant amounts of brightener were consumed during plating.
However, a slight improvement in protecting brightener was noted
when the current density was in the about 0-12 ASF range.
Semi-bright panels were produced. The control panel without iron
had a semi-bright surface when the current density was reduced to
about 0-60 ASF range.
[0085] The additive consumption inhibiting compounds of Example 1
above showed improved brightener protection in contrast to iron
salts at a current density of about 5-90 ASF. The brightener in the
plating bath with the iron salts and in the control bath was
substantially consumed after about 10 minutes resulting in no fully
bright panels in contrast to the plating baths of Example 1 where
the addition of the additive consumption inhibiting compounds to
the plating baths produced numerous bright panels.
Example 4
[0086] Other transition metals in addition to iron were tested for
their ability to prevent brightener consumption in acid copper
plating baths.
[0087] Five baths were prepared with about 80 g/L of copper sulfate
pentahydrate, about 225 g/L of sulfuric acid, about 1 g/L of
polyethylene oxide and about 1 ppm of bissulfopropyl disulfide
(brightener). One bath contained about 10 g/L of Na.sub.2MoO.sub.4,
a second bath contained about 10 g/L of MnSO.sub.4, a third bath
contained about 1 g/L of MnSO.sub.4 and a fourth bath contained
about 1 g/L of TeO.sub.2. A fifth bath acted as a control and
contained no transition metal compounds. Brightener consumption was
tested in Hull Cells employing copper clad FR4/glass-epoxy panels
as the cathode and an IrO2 coated titanium anode. Electroplating
was performed for about 10 minutes at about 3 amps using a DC
rectifier with air agitation. Current density was in the range of
about 5-90 ASF.
[0088] Although the baths containing the transition elements
produced panels that were semi-bright in contrast to the control
panel, none of the baths produced fully bright cathodes in the
about 5-90 ASF current density range. Just as with the iron (II)
sulfate of Example 3, the baths containing the transition metal
salts provided copper deposits that were slightly brighter than the
control.
[0089] The additive consumption inhibiting compounds of the present
invention as shown in Example 1 above had improved brightener
preservation activity in contrast to the transition metal salts of
the present example. Several fully bright panels were produced with
plating baths containing the additive consumption inhibiting
compounds of Example 1 in contrast to none with baths containing
the transition elements.
* * * * *