U.S. patent application number 15/212713 was filed with the patent office on 2018-01-18 for indium electroplating compositions and methods for electroplating indium.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Kristen Flajslik, Mark Lefebvre, Yi Qin.
Application Number | 20180016689 15/212713 |
Document ID | / |
Family ID | 59350820 |
Filed Date | 2018-01-18 |
United States Patent
Application |
20180016689 |
Kind Code |
A1 |
Qin; Yi ; et al. |
January 18, 2018 |
INDIUM ELECTROPLATING COMPOSITIONS AND METHODS FOR ELECTROPLATING
INDIUM
Abstract
Indium electroplating compositions electroplate substantially
defect-free uniform layers which have a smooth surface morphology
on metal layers. The indium electroplating compositions can be used
to electroplate indium metal on metal layers of various substrates
such as semiconductor wafers and as thermal interface
materials.
Inventors: |
Qin; Yi; (Westborough,
MA) ; Flajslik; Kristen; (Hopkinton, MA) ;
Lefebvre; Mark; (Hudson, NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Family ID: |
59350820 |
Appl. No.: |
15/212713 |
Filed: |
July 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 3/54 20130101 |
International
Class: |
C25D 3/54 20060101
C25D003/54 |
Claims
1: An indium electroplating composition comprising one or more
sources of indium ions, wherein the one or more sources of indium
ions are chosen from indium salts of alkane sulfonic acids, indium
salts of aromatic sulfonic acids, indium salts of sulfamic acid,
sulfate salts of indium, nitrate salts of indium, hydroxide salts
of indium, indium oxides, fluoroborate salts of indium, indium
salts of carboxylic acids and indium salts of amino acids, one or
more thiourea derivatives and citric acid, salts thereof or
mixtures thereof, wherein the indium electroplating composition is
free of alloying metals, and, wherein a pH of the indium
electroplating composition is 1-4.
2: The indium electroplating composition of claim 1, wherein the
thiourea derivatives are chosen from guanylthiourea,
1-allyl-2-thiourea, 1-acetyl-2-thiourea, 1-benzoyl-2-thiourea,
1-benzyl-2-thiourea, 1-butyl-3-phenyl-2-thiourea,
1,1-dimethyl-2-thiourea, tetramethyl-2-thiourea, 1,3-dimethyl
thiourea, 1-methyl thiourea, 1,3-diethyl thiourea,
1,1-diphenyl-2-thiourea, 1,3-diphenyl-2-thiourea,
1,1-dipropyl-2-thiourea, 1,3-dipropyl-2-thiourea,
1,3-diisopropyl-2-thiourea, 1,3-di(2-tolyl)-2-thiourea,
1-methyl-3-phenyl-2-thiourea, 1(1-naphthyl)-3-phenyl-2-thiourea,
1(1-naphthyl)-2-thiourea, 1(2-naphthyl)-2-thiourea,
1-phenyl-2-thiourea, 1,1,3,3-tetramethyl-2-thiourea and
1,1,3,3-tetraphenyl-2-thiourea.
3: The indium electroplating composition of claim 2, wherein the
thiourea derivatives are chosen from guanylthiourea,
1-allyl-2-thiourea and tetramethyl-2-thiourea.
4: The indium electroplating composition of claim 1, wherein the
one or more thiourea derivatives is included in the composition in
amounts of 0.01 g/L to 50 g/L.
5: The indium electroplating composition of claim 1, wherein the
composition further comprises one or more sources of chloride ions,
wherein a molar ratio of the chloride ions to the indium ions is
2:1 or greater.
6: The indium electroplating composition of claim 5, wherein the
molar ratio of chloride ions to indium ions is 2:1 to 7:1.
7: The indium electroplating composition of claim 6, wherein the
molar ratio of chloride ions to indium ions is 4:1 to 6:1.
8: The indium electroplating composition of claim 1, further
comprising one or more surfactants chosen from amine surfactants,
ethoxylated naphthols, sulfonated naphthol polyethers, (alkyl)
phenol ethoxylates, sulfonated alkylalkoxylates, alkylene glycol
alkyl ethers and sulfopropylated polyalkoxylated beta-naphthol
alkali salts.
9: The indium electroplating composition of claim 1, further
comprising one or more copolymers of a reaction product of
epihalohydrin and one or more nitrogen-containing organic
compounds.
10: A method comprising: a) providing a substrate comprising a
metal layer; b) contacting the substrate with an indium
electroplating composition comprising one or more sources of indium
ions, wherein the one or more sources of indium ions are chosen
from indium salts of alkane sulfonic acids, indium salts of
aromatic sulfonic acids, indium salts of sulfamic acid, sulfate
salts of indium, nitrate salts of indium, hydroxide salts of
indium, indium oxides, fluoroborate salts of indium, indium salts
of carboxylic acids and indium salts of amino acids, one or more
thiourea derivatives and citric acid, salt of citric acid or
mixtures thereof, wherein the indium electroplating composition is
free of alloying metals, and, wherein a pH of the indium
electroplating composition is 1-4; and c) electroplating an indium
metal layer on the metal layer of the substrate with the indium
electroplating composition.
11: The method of claim 10, wherein the one or more thiourea
derivatives is included in the indium electroplating composition in
amounts of 0.01 g/L to 50 g/L.
12: The method of claim 10, wherein the indium electroplating
composition further comprises one or more sources of chloride ions,
wherein a molar ratio of the chloride ions to the indium ions is
2:1 or greater.
13: The method of claim 10, wherein the metal layer is nickel,
copper, gold or tin.
14: The method of claim 13, wherein the metal layer is nickel.
15: The method of claim 10, wherein the metal layer is 10 nm to 100
.mu.m thick.
16: The method of claim 10, wherein the indium metal layer is 10 nm
to 100 .mu.m thick.
17: The indium electroplating composition of claim 1, wherein the
pH is from 2-3.
18: The method of claim 10, wherein the pH of the indium
electroplating composition is from 2-3.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to indium electroplating
compositions and methods for electroplating indium metal on metal
layers. More specifically, the present invention is directed to
indium electroplating compositions and methods of electroplating
indium metal on metal layers where the indium metal deposit is
uniform, substantially void-free and has a smooth surface
morphology.
BACKGROUND OF THE INVENTION
[0002] The ability to reproducibly plate void-free uniform indium
of target thickness and smooth surface morphology on metal layers
is challenging. Indium reduction occurs at potentials more negative
than that of proton reduction, and significant hydrogen bubbling at
the cathode causes increased surface roughness. Indium (1.sup.+)
ions, stabilized due to the inert pair effect, formed in the
process of indium deposition catalyze proton reduction and
participate in disproportionation reactions to regenerate Indium
(3.sup.+) ions. In the absence of a complexing agent, indium ions
begin to precipitate from solutions above pH>3. Plating indium
on metals such as nickel, tin, copper and gold is challenging
because these metals are good catalysts for proton reduction and
are more noble than indium, thus they can cause corrosion of indium
in a galvanic interaction. Indium may also form undesired
intermetallic compounds with these metals. Finally, indium
chemistry and electrochemistry have not been well studied, thus
interactions with compounds that may serve as additives are
unknown.
[0003] In general, conventional indium electroplating baths have
not been able to electroplate an indium deposit which is compatible
with multiple under bump metals (UBM) such as nickel, copper, gold
and tin. More importantly, conventional indium electroplating baths
have not been able to electroplate indium with high coplanarity and
high surface planarity on substrates which include nickel. Indium,
however, is a highly desirable metal in numerous industries because
of its unique physical properties. For example, it is sufficiently
soft such that it readily deforms and fills in microstructures
between two mating parts, has a low melting temperature
(156.degree. C.) and a high thermal conductivity (.about.82
W/m.degree. K), good electrical conductivity, good ability to alloy
and form intermetallic compounds with other metals in a stack. It
may be used as low temperature solder bump material, a desired
process for 3D stack assembly to reduce damage on assembled chips
by the thermal stress induced during reflow processing. Such
properties enable indium for various uses in the electronics and
related industries including in semiconductors and polycrystalline
thin film solar cells.
[0004] Indium can also be used as thermal interface materials
(TIMs). TIMs are critical to protect electronic devices such as
integrated circuits (IC) and active semiconductor devices, for
example, microprocessors, from exceeding their operational
temperature limit. They enable bonding of the heat generating
device (e.g. a silicon semiconductor) to a heat sink or a heat
spreader (e.g. copper and aluminum components) without creating an
excessive thermal barrier. The TIM may also be used in assembly of
other components of the heat sink or the heat spreader stack that
composes the overall thermal impedance path.
[0005] Several classes of materials are being used as TIMs, for
example, thermal greases, thermal gels, adhesives, elastomers,
thermal pads, and phase change materials. Although the foregoing
TIMs have been adequate for many semiconductor devices, the
increased performance of semiconductor devices has rendered such
TIMs inadequate. Thermal conductivity of many current TIMs does not
exceed 5 W/m.degree. K and many are less than 1 W/m.degree. K.
However, TIMs that form thermal interfaces with effective thermal
conductivities exceeding 15 W/m.degree. K are presently needed.
[0006] Accordingly, indium is a highly desirable metal for
electronic devices, and there is a need for an improved indium
composition for electroplating indium metal, in particular, indium
metal layers on metal substrates.
SUMMARY OF THE INVENTION
[0007] Compositions include one or more sources of indium ions, one
or more of thiourea and thiourea derivatives and citric acid, salts
thereof or mixtures thereof.
[0008] Methods include providing a substrate including a metal
layer; contacting the substrate with an indium electroplating
composition including one or more sources of indium ions, one or
more of thiourea and thiourea derivatives and citric acid, salts of
citric acid or mixtures thereof; and electroplating an indium metal
layer on the metal layer of the substrate with the indium
electroplating composition.
[0009] The indium electroplating compositions can provide a deposit
of indium metal on a metal layer which is substantially void-free,
uniform and has smooth morphology. The ability to reproducibly
plate a void-free uniform indium of target thickness, and smooth
surface morphology enables the expanded use of indium in the
electronics industry, including in semiconductors and
polycrystalline thin film solar cells. The indium deposited from
the electroplating composition of the present invention can be used
as a low temperature solder material which is desired for 3D stack
assembly to reduce damage on assembled chips by the thermal stress
induced during reflow processing. The indium can also be used as
thermal interface materials to protect electronic devices such as
microprocessors and integrated circuits. The present invention
addresses a number of problems of the prior inability to
electroplate indium of sufficient properties to meet requirements
for applications in advanced electronic devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is an optical microscope image of a nickel plated
via having a diameter of 75 .mu.m.
[0011] FIG. 1B is an optical microscope image of an indium layer on
a nickel plated via having a diameter of 75 .mu.m.
[0012] FIG. 2 is an optical microscope image of an indium layer on
a nickel plated via having a diameter of 75 .mu.m where the indium
was electroplated from an indium composition containing
guanylthiourea.
[0013] FIG. 3 is an optical microscope image of an indium layer on
a nickel plated via having a diameter of 75 .mu.m where the indium
was electroplated from an indium composition containing
tetramethyl-2-thiourea.
[0014] FIG. 4 is an optical microscope image of an indium layer on
a nickel plated rectangular via having a length of 50 .mu.m where
the indium was electroplated from an indium composition containing
1-allyl-2-thiourea.
[0015] FIG. 5 is an optical microscope image of an indium layer on
a nickel plated via having a diameter of 75 .mu.m where the indium
was electroplated from an indium composition containing
guanylthiourea and sodium chloride.
DETAILED DESCRIPTION OF THE INVENTIONS
[0016] As used throughout the specification, the following
abbreviations have the following meanings, unless the context
clearly indicates otherwise: .degree. C.=degrees Centigrade;
.degree. K=degrees Kelvin; g=gram; mg=milligram; L=liter;
A=amperes; dm=decimeter; ASD=A/dm.sup.2=current density;
.mu.m=micron=micrometer; ppm=parts per million; ppb=parts per
billion; ppm=mg/L; indium ion=In.sup.3+; Li.sup.+=lithium ion;
Na.sup.+=sodium ion; K.sup.+=potassium ion; NH.sub.4.sup.+=ammonium
ion; nm=nanometers=10.sup.-9 meters; .mu.m=micrometers=10.sup.-6
meters; M=molar; MEMS=micro-electro-mechanical systems; TIM=thermal
interface material; IC=integrated circuits; EO=ethylene oxide and
PO=propylene oxide.
[0017] The terms "depositing", "plating" and "electroplating" are
used interchangeably throughout this specification. The term
"copolymer" is a compound composed of two or more different mers.
The term "dendrite" means branching spike-like metal crystals.
Unless otherwise noted all plating baths are aqueous solvent based,
i.e. water based, plating baths. All amounts are percent by weight
and all ratios are by moles, unless otherwise noted. All numerical
ranges are inclusive and combinable in any order except where it is
logical that such numerical ranges are constrained to add up to
100%.
[0018] The compositions include one or more sources of indium ions
which are soluble in an aqueous environment. The indium
compositions are free of alloying metals. Such sources include, but
are not limited to, indium salts of alkane sulfonic acids and
aromatic sulfonic acids, such as methanesulfonic acid,
ethanesulfonic acid, butane sulfonic acid, benzenesulfonic acid and
toluenesulfonic acid, indium salts of sulfamic acid, sulfate salts
of indium, chloride and bromide salts of indium, nitrate salts,
hydroxide salts, indium oxides, fluoroborate salts, indium salts of
carboxylic acids, such as citric acid, acetoacetic acid, glyoxylic
acid, pyruvic acid, glycolic acid, malonic acid, hydroxamic acid,
iminodiacetic acid, salicylic acid, glyceric acid, succinic acid,
malic acid, tartaric acid, hydroxybutyric acid, indium salts of
amino acids, such as arginine, aspartic acid, asparagine, glutamic
acid, glycine, glutamine, leucine, lysine, threonine, isoleucine,
and valine. Typically, the source of indium ions is one or more
indium salts of sulfuric acid, sulfamic acid, alkane sulfonic
acids, aromatic sulfonic acids and carboxylic acids. More
typically, the source of indium ions is one or more indium salts of
sulfuric acid and sulfamic acid.
[0019] The water-soluble salts of indium are included in the
compositions in sufficient amounts to provide an indium deposit of
the desired thickness. Preferably the water-soluble indium salts
are included in the compositions to provide indium (3.sup.+) ions
in the compositions in amounts of 2 g/L to 70 g/L, more preferably
from 2 g/L to 60 g/L, most preferably from 2 g/L to 30 g/L.
[0020] Citric acid, salts thereof or mixtures thereof is included
in the indium compositions. Citric acid salts include, but are not
limited to sodium citrate dihydrate, monosodium citrate, potassium
citrate and diammonium citrate. Citric acid, salts thereof or
mixtures thereof can be included in amounts of 5 g/L to 300 g/L,
preferably from 50 g/L to 200 g/L. Preferably a mixture of citric
acid and its salts are included in the indium compositions in the
foregoing amounts.
[0021] One or more of thiourea and thiourea derivatives are
included in the indium compositions. Thiourea derivatives include
but are not limited to guanylthiourea, 1-allyl-2-thiourea,
1-acetyl-2-thiourea, 1-benzoyl-2-thiourea, 1-benzyl-2-thiourea,
1-butyl-3-phenyl-2-thiourea, 1,1-dimethyl-2-thiourea,
tetramethyl-2-thiourea, 1,3-dimethyl thiourea, 1-methyl thiourea,
1,3-diethyl thiourea, 1,1-diphenyl-2-thiourea,
1,3-diphenyl-2-thiourea, 1,1-dipropyl-2-thiourea,
1,3-dipropyl-2-thiourea, 1,3-diisopropyl-2-thiourea,
1,3-di(2-tolyl)-2-thiourea, 1-methyl-3-phenyl-2-thiourea,
1(1-naphthyl)-3-phenyl-2-thiourea, 1(1-naphthyl)-2-thiourea,
1(2-naphthyl)-2-thiourea, 1-phenyl-2-thiourea,
1,1,3,3-tetramethyl-2-thiourea and 1,1,3,3-tetraphenyl-2-thiourea.
Preferably the thiourea derivative is chosen from guanylthiourea,
1-allyl-2-thiourea and tetramethyl-2-thiourea. More preferably the
thiourea derivative is chosen from guanylthiourea. Thiourea and
thiourea derivatives are included in amounts of 0.01 g/L to 50 g/L,
preferably from 0.1 g/L to 35 g/L, more preferably from 0.1 g/L to
5 g/L.
[0022] Optionally, but preferably, one or more sources of chloride
ions are included in the indium electroplating compositions.
Sources of chloride ions include, but are not limited to sodium
chloride, potassium chloride, hydrogen chloride or mixtures
thereof. Preferably the source of chloride ions is sodium chloride,
potassium chloride or mixtures thereof. More preferably the source
of chloride ions is sodium chloride. One or more sources of
chloride ions are included in the indium compositions such that a
molar ratio of chloride ions to indium ions is at least 2:1,
preferably from 2:1 to 7:1, more preferably from 4:1 to 6:1.
[0023] Optionally, in addition to citric acid, its salts or
mixtures thereof, one or more additional buffers can be included in
the indium compositions to provide a pH of 1-4, preferably from
2-3. The buffer includes an acid and the salt of its conjugate
base. Acids include amino acids, carboxylic acids, glyoxylic acid,
pyruvic acid, hydroxamic acid, iminodiacetic acid, salicylic acid,
succinic acid, hydroxybutyric acid, acetic acid, acetoacetic acid,
tartaric acid, phosphoric acid, oxalic acid, carbonic acid,
ascorbic acid, boric acid, butanoic acid, thioacetic acid, glycolic
acid, malic acid, formic acid, heptanoic acid, hexanoic acid,
hydrofluoric acid, lactic acid, nitrous acid, octanoic acid,
pentanoic acid, uric acid, nonanoic acid, decanoic acid, sulfurous
acid, sulfuric acid, alkane sulfonic acids and aryl sulfonic acids
such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic
acid, toluenesulfonic acid, sulfamic acid. The acids are combined
with Li.sup.+, Na.sup.+, K.sup.+, NH.sub.4.sup.+ or
(C.sub.nH.sub.(2n+1)).sub.4N.sup.+ salts of conjugate bases where n
is an integer from 1 to 6.
[0024] Optionally, one or more surfactants can be included in the
indium compositions. Such surfactants include, but are not limited
to amine surfactants such as quaternary amines, commercially
available as TOMAMINE.RTM.-Q-C-15 surfactant, amine oxides,
commercially available as TOMAMINE.RTM.-AO-455 surfactant, both
available from Air Products; hydrophilic polyether monoamine
commercially available as SURFONAMINE.RTM. L-207 amine surfactant
from Huntsman; polyethyleneglycol octyl (3-sulfopropyl) diether
commercially available as RALUFON.RTM. EA 15-90 surfactant;
[(3-sulfopropoxy)-polyalkoxy]-.beta.-naphthyl ether, potassium
salt, commercially available as RALUFON.RTM. NAPE 14-90 surfactant,
octaethyleneglycol octyl ether, commercially available as
RALUFON.RTM. EN 16-80 surfactant, polyethyleneglycol alkyl
(3-sulfopropyl) diether, potassium salt, commercially available as
RALUFON.RTM. F 11-3 surfactant, all are obtainable from Raschig
GmbH; EO/PO block copolymers, commercially available as
TETRONIC.RTM.-304 surfactant, available from BSF; ethoxylated
.beta.-naphthol from Schaerer & Schlaepfer AG such as
ADUXOL.TM. NAP-08, ADUXOL.TM. NAP-03, ADUXOL.TM. NAP-06;
ethoxylated 2,4,7,9-Tetramethyl-5-decyne-4,7-diol such as
SURFYNOL.RTM. 484 surfactant from Air Products and Chemicals Co.;
LUX.TM. BN-13 surfactant, ethoxylated .beta.-naphthol, such as TIB
Chemicals LUX.TM. NPS surfactant; ethoxylated-.beta.-naphthols such
as POLYMAX.RTM. PA-31 surfactant available from PCC Chemax, Inc.
Such surfactants are included in amounts of 1 ppm to 10 g/L,
preferably from 5 ppm to 5 g/L.
[0025] Optionally, the indium compositions can include one or more
grain refiners. Such grain refiners include, but are not limited to
2-picolinic acid, Sodium 2-naphthol-7-sulfonate,
3-(benzothiazol-2-ylthio)propane-1-sulfonic acid (ZPS),
3-(carbamimidoylthio)propane-1-sulfonic acid (UPS),
bis(sulfopropyl)disulfide (SPS), mercaptopropane sulfonic acid
(MPS), 3-N,N-dimethylaminodithiocarbamoyl-1-propane sulfonic acid
(DPS), and (O-ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX).
Preferably such grain refiners are included in the indium
compositions in amounts of 0.1 ppm to 5 g/L, more preferably from
0.5 ppm to 1 g/L.
[0026] Optionally, the one or more suppressors can be included in
the indium compositions. Suppressors include, but are not limited
to, phenanthroline and its derivatives, such as 1,10-phenantroline,
triethanolamine and its derivatives, such as triethanolamine lauryl
sulfate, sodium lauryl sulfate and ethoxylated ammonium lauryl
sulfate, polyethyleneimine and its derivatives, such as
hydroxypropylpolyeneimine (HPPEI-200), and alkoxylated polymers.
Such suppressors are included in the indium compositions in
conventional amounts. Typically, suppressors are included in
amounts of 1 ppm to 5 g/L.
[0027] Optionally, one or more levelers can be included in the
indium compositions. Levelers include, but are not limited to,
polyalkylene glycol ethers. Such ethers include, but are not
limited to, dimethyl polyethylene glycol ether, di-tertiary butyl
polyethylene glycol ether, polyethylene/polypropylene dimethyl
ether (mixed or block copolymers), and octyl monomethyl
polyalkylene ether (mixed or block copolymer). Such levelers are
included in conventional amounts. In general, such levelers are
included in amounts of 100 ppb to 500 ppb.
[0028] Optionally, one or more hydrogen suppressors can included in
the indium compositions to suppress hydrogen gas formation during
indium metal electroplating. Hydrogen suppressors include
epihalohydrin copolymers. Epihalohydrins include epichlorohydrin
and epibromohydrin. Typically, copolymers of epichlorohydrin are
used. Such copolymers are water-soluble polymerization products of
epichlorohydrin or epibromohydrin and one or more organic compounds
which includes nitrogen, sulfur, oxygen atoms or combinations
thereof.
[0029] Nitrogen-containing organic compounds copolymerizable with
epihalohydrins include, but are not limited to: [0030] 1) aliphatic
chain amines; [0031] 2) unsubstituted heterocyclic nitrogen
compounds having at least two reactive nitrogen sites; and, [0032]
3) substituted heterocyclic nitrogen compounds having at least two
reactive nitrogen sites and having 1-2 substitution groups chosen
from alkyl groups, aryl groups, nitro groups, halogens and amino
groups.
[0033] Aliphatic chain amines include, but are not limited to,
dimethylamine, ethylamine, methylamine, diethylamine, triethyl
amine, ethylene diamine, diethylenetriamine, propylamine,
butylamine, pentylamine, hexylamine, heptylamine, octylamine,
2-ethylhexylamine, isooctylamine, nonylamine, isononylamine,
decylamine, undecylamine, dodecylaminetridecylamine and alkanol
amines.
[0034] Unsubstituted heterocyclic nitrogen compounds having at
least two reactive nitrogen sites include, but are not limited to,
imidazole, imidazoline, pyrazole, 1,2,3-triazole, tetrazole,
pyridazine, 1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-thiadiazole and
1,3,4-thiadiazole.
[0035] Substituted heterocyclic nitrogen compounds having at least
two reactive nitrogen sites and having 1-2 substitutions groups
include, but are not limited to, benzimidazole, 1-methylimidazole,
2-methylimidazole, 1,3-dimethylimidazole, 4-hydroxy-2-amino
imidazole, 5-ethyl-4-hydroxyimidazole, 2-phenylimidazoline and
2-tolylimidazoline.
[0036] Preferably, one or more compounds chosen from imidazole,
pyrazole, imidazoline, 1,2,3-triazole, tetrazole, pyridazine,
1,2,4-triazole, 1,2,3-oxadiazole, 1,2,4-thiadiazole and
1,3,4-thiadiazole and derivatives thereof which incorporate 1 or 2
substituents chosen from methyl, ethyl, phenyl and amino groups are
used to form the epihalohydrin copolymer.
[0037] Some of the epihalohydrin copolymers are commercially
available such as from Raschig GmbH, Ludwigshafen Germany and from
BASF, Wyandotte, Mich., USA, or may be made by methods disclosed in
the literature. An example of a commercially available
imidazole/epichlorohydrin copolymer is LUGALVAN.RTM. IZE copolymer,
obtainable from BASF.
[0038] Epihalohydrin copolymers can be formed by reacting
epihalohydrins with the nitrogen, sulfur or oxygen containing
compounds described above under any suitable reaction conditions.
For example, in one method, both materials are dissolved in
suitable concentrations in a body of mutual solvent and reacted
therein at, for example, 45 to 240 minutes. The aqueous solution
chemical product of the reaction is isolated by distilling off the
solvent and then is added to the body of water which serves as the
electroplating solution, once the indium salt is dissolved. In
another method these two materials are placed in water and heated
to 60.degree. C. with constant vigorous stirring until they
dissolve in the water as they react.
[0039] A wide range of ratios of the reaction compound to
epihalohydrin can be used, such as from 0.5:1 to 2:1 moles.
Typically the molar ratio is from 0.6:1 to 2:1 moles, more
typically the molar ratio is 0.7 to 1:1, most typically the molar
ratio is 1:1.
[0040] Additionally, the reaction product may be further reacted
with one or more reagents before the electroplating composition is
completed by the addition of indium salt. Thus, the described
product may be further reacted with a reagent which is at least one
of ammonia, aliphatic amine, polyamine and polyimine. Typically,
the reagent is at least one of ammonia, ethylenediamine,
tetraethylene pentamine and a polyethyleneimine having a molecular
weight of at least 150, although other species meeting the
definitions set forth herein may be used. The reaction can take
place in water with stirring.
[0041] For example, the reaction between the reaction product of
epichlorohydrin and a nitrogen-containing organic compound as
described above and a reagent chosen from one or more of ammonia,
aliphatic amine, and arylamine or polyimine can take place and can
be carried out at a temperature of, for example, 30.degree. C. to
60.degree. C. for, example, 45 to 240 minutes. The molar ratio
between the reaction product of the nitrogen containing
compound-epichlorohydrin reaction and the reagent is typically
1:0.3-1.
[0042] The epihalohydrin copolymers are included in the
compositions in amounts of 0.01 g/L to 100 g/L. preferably,
epihalohydrin copolymers are included in amounts of 0.1 g/L to 80
g/L, more preferably, they are included in amounts of 0.1 g/L to 50
g/L, most preferably in amounts of 1 g/L to 30 g/L.
[0043] The indium compositions may be used to deposit substantially
uniform, void-free, indium metal layers on metal layers of various
substrates. The indium layers are also substantially dendrite-free.
The indium layers preferably range in thickness from 10 nm to 100
.mu.m, more preferably from 100 nm to 75 .mu.m.
[0044] Apparatus used to deposit indium metal on metal layers is
conventional. Preferably conventional soluble indium electrodes are
used as the anode. Any suitable reference electrode may be used.
Typically, the reference electrode is a silver chloride/silver
electrode. Current densities may range from 0.1 ASD to 10 ASD,
preferably from 0.1 to 5 ASD, more preferably from 1 to 4 ASD.
[0045] The temperatures of the indium compositions during indium
metal electroplating can range from room temperature to 80.degree.
C. Preferably, the temperatures range from room temperature to
65.degree. C., more preferably from room temperature to 60.degree.
C. Most preferably the temperature is room temperature.
[0046] The indium compositions may be used to electroplate indium
metal on nickel, copper, gold and tin layers of various substrates,
including components for electronic devices, for magnetic field
devices and superconductivity MRIs. Preferably indium is
electroplated on nickel. The metal layers preferably range from 10
nm to 100 .mu.m, more preferably from 100 nm to 75 .mu.m. The
indium compositions may also be used with conventional photoimaging
methods to electroplate indium metal small diameter solder bumps on
various substrates such as silicon wafers. Small diameter bumps
preferably have diameters of 1 .mu.m to 100 .mu.m, more preferably
from 2 .mu.m to 50 .mu.m, with aspect ratios of 1 to 3.
[0047] For example, the indium compositions may be used to
electroplate indium metal on a component for an electrical device
to function as a TIM, such as for, but not limited to, ICs,
microprocessors of semiconductor devices, MEMS and components for
optoelectronic devices. Such electronic components may be included
in printed wiring boards and hermetically sealed chip-scale and
wafer-level packages. Such packages typically include an enclosed
volume which is hermetically sealed, formed between a base
substrate and lid, with the electronic device being disposed in the
enclosed volume. The packages provide for containment and
protection of the enclosed device from contamination and water
vapor in the atmosphere outside the package. The presence of
contamination and water vapor in the package can give rise to
problems such as corrosion of metal parts as well as optical losses
in the case of optoelectronic devices and other optical components.
The low melting temperature (156.degree. C.) and high thermal
conductivity (.about.82 W/m.degree. K) are properties which make
indium metal highly desirable for use as a TIM.
[0048] In addition to TIMs, the indium compositions may be used to
electroplate underlayers on substrates to prevent whisker formation
in electronic devices. The substrates include, but are not limited
to, electrical or electronic components or parts such as film
carriers for mounting semiconductor chips, printed circuit boards,
lead frames, contacting elements such as contacts or terminals and
plated structural members which demand good appearance and high
operation reliability.
[0049] The following examples further illustrate the invention, but
are not intended to limit the scope of the invention.
Example 1 (Comparative)
[0050] Photoresist patterned silicon wafers from Silicon Valley
Microelectronics, Inc. with a plurality of vias having a diameter
of 75 .mu.m and copper seed layer at the base of each via were
electroplated with a nickel layer using NIKAL.TM. BP nickel
electroplating bath available from Dow Advanced Materials. Nickel
electroplating was done at 55.degree. C., with a cathode current
density of 1 ASD for 120 seconds. A conventional rectifier supplied
the current. The anode was a soluble nickel electrode. After
plating the silicon wafer was removed from the plating bath, the
photoresist was stripped from the wafers with SHIPLEY BPR.TM.
Photostripper available from Dow Advanced Materials and rinsed with
water. The nickel deposits appeared substantially smooth and
without any observable dendrites on the surface. FIG. 1A is an
optical image of one of the nickel plated copper seed layers taken
with a LEICA.TM. optical microscope.
[0051] The following aqueous indium electrolytic composition was
prepared:
TABLE-US-00001 TABLE 1 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L
[0052] The foregoing nickel layer electroplating process was
repeated on another set of photoresist patterned wafers except that
after electroplating the nickel layer, the nickel plated silicon
wafers were immersed in the indium electroplating composition and
an indium metal layer was electroplated on the nickel. Indium
electroplating was done at 25.degree. C. at a current density of
4ASD for 30 seconds. The pH of the indium electroplating
composition was 2.4. The anode was an indium soluble electrode.
After the indium was plated on the nickel, the photoresist was
stripped from the wafers and the morphology of the indium deposits
was observed. All of the indium deposits appeared rough.
[0053] FIG. 1B is an optical image of one of the indium metal
deposits electroplated on the nickel layer. The indium deposit was
very rough in contrast to the nickel deposit as shown in FIG.
1A.
Example 2
[0054] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00002 TABLE 2 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L Guanylthiourea
0.75 g/L
[0055] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 30 seconds. The pH of the composition
was 2.4. The anode was an indium soluble electrode. After indium
was electroplated on the nickel layers, the photoresist was
stripped from the wafers and the indium morphology was observed.
All of the indium deposits appeared uniform and smooth.
[0056] FIG. 2 is an optical microscope image of one of the indium
metal deposits electroplated on the nickel layer. The indium
deposit appeared smooth in contrast to the indium deposit of FIG.
1B.
Example 3
[0057] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00003 TABLE 3 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L
Tetramethyl-2-thiourea 0.5 g/L
[0058] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 30 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth.
[0059] FIG. 3 is an optical microscope image of one of the indium
metal deposits electroplated on the nickel. The indium deposit
appeared smooth in contrast to the indium deposit of FIG. 1B.
Example 4
[0060] The method described in Example 1 above was repeated except
that the silicon wafers were patterned with photoresist to have
rectangular vias having lengths of 50 .mu.m and the indium
electroplating composition included the following components:
TABLE-US-00004 TABLE 4 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L
1-allyl-2-thiourea.sup.1 1 g/L .sup.1synonym = N-allyl-thiourea
[0061] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 11 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth.
[0062] FIG. 4 is an optical microscope image of one of the indium
metal deposits electroplated on the nickel layer. The indium
deposit appeared smooth in contrast to the indium deposit of FIG.
1B.
Example 5
[0063] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00005 TABLE 5 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L Guanylthiourea
0.75 g/L Quaternary amine surfactant.sup.2 5 ppm .sup.2TOMAMINE
.RTM. QC-15 surfactant available from Air Products
[0064] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 11 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth substantially the same as shown in FIGS. 2-4.
Example 6
[0065] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00006 TABLE 6 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L Guanylthiourea
0.75 g/L Polyethyleneglycol octyl (3-sulfopropyl) diether.sup.3 10
ppm .sup.3RALUFON .RTM. EA 15-90 surfactant available from
Raschig
[0066] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 11 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth substantially the same as shown in FIGS. 2-4.
Example 7
[0067] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00007 TABLE 7 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L Guanylthiourea
0.75 g/L Quaternary amine surfactant.sup.4 5 ppm Sodium
2-naphthol-7-sulfonate 100 ppm .sup.4TOMAMINE .RTM. QC-15
surfactant available from Air Products
[0068] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 11 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth substantially the same as shown in FIGS. 2-4.
Example 8
[0069] The method described in Example 1 above was repeated except
that the indium electroplating composition included the following
components:
TABLE-US-00008 TABLE 8 COMPONENT AMOUNT Indium sulfate 45 g/L
Citric acid 96 g/L Sodium citrate dihydrate 59 g/L Guanylthiourea
0.15 g/L Sodium chloride.sup.5 50 g/L .sup.5Molar ratio of
chloride:indium ions = 5:1
[0070] The nickel plated silicon wafers were immersed in the indium
electroplating composition and indium metal was electroplated on
the nickel. Indium electroplating was done at 25.degree. C. at a
current density of 4ASD for 30 seconds. The pH of the composition
was 2.4. After indium was electroplated on the nickel layers, the
photoresist was stripped from the wafers and the indium morphology
was observed. All of the indium deposits appeared uniform and
smooth. FIG. 5 is an optical microscope image of the indium
electroplated from the bath of Table 8. As shown in FIG. 5 the
indium deposit was uniform and smooth.
* * * * *