U.S. patent application number 12/389649 was filed with the patent office on 2010-08-26 for process for inhibiting oxide formation on copper surfaces.
This patent application is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to Jeffery Scott Thompson.
Application Number | 20100215841 12/389649 |
Document ID | / |
Family ID | 42631199 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100215841 |
Kind Code |
A1 |
Thompson; Jeffery Scott |
August 26, 2010 |
PROCESS FOR INHIBITING OXIDE FORMATION ON COPPER SURFACES
Abstract
This invention provides processes for inhibiting the formation
of copper oxides on substantially oxide-free copper surfaces by
contacting a substantially oxide-free copper surface with a
bifunctional ligand that contains both a metal-coordinating group
and a tertiary amine group in an aqueous solution of pH about 2 to
about 5.5. A thin layer of the bifunctional ligand formed by
coordination of the dialkylaminoacetonitrile to the copper surface
can be removed by heating under vacuum to re-generate a
substantially oxide-free copper surface.
Inventors: |
Thompson; Jeffery Scott;
(West Chester, PA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
42631199 |
Appl. No.: |
12/389649 |
Filed: |
February 20, 2009 |
Current U.S.
Class: |
427/96.4 ;
106/14.05; 106/287.27; 106/287.3 |
Current CPC
Class: |
H01L 21/02074 20130101;
H01L 21/02063 20130101; H01L 21/76814 20130101; C23G 1/103
20130101; H05K 2203/122 20130101; C23C 16/0227 20130101; H05K 3/282
20130101; C11D 7/3209 20130101; C09D 5/086 20130101; H01L 21/76883
20130101; C09D 5/008 20130101; H01L 21/321 20130101 |
Class at
Publication: |
427/96.4 ;
106/287.3; 106/14.05; 106/287.27 |
International
Class: |
B05D 5/12 20060101
B05D005/12; C09D 5/00 20060101 C09D005/00; C09D 5/08 20060101
C09D005/08 |
Claims
1. A process comprising contacting a substantially oxide-free
copper surface with an aqueous solution comprising a bifunctional
ligand for a sufficient period of time to form a copper surface
coated with a layer of the bifunctional ligand, wherein the
bifunctional ligand comprises a nitrile group and a tertiary amine
group attached to a carbon atom adjacent to the nitrile group, and
the pH of the solution is about 2 to about 5.5.
2. The process of claim 1 wherein the layer of bifunctional ligand
is from about 5 to about 50 Angstroms thick.
3. The process of claim 1, wherein the aqueous solution further
comprises one or more additives selected from the group consisting
of chelating agents, corrosion-inhibiting compounds, surface-active
agents, organic solvents, fluorides, fluoride equivalents,
anti-corrosive agents, and surfactants.
4. The process of claim 1, further comprising rinsing and/or drying
the coated copper surface.
5. The process of claim 4, further comprising heating the coated
copper surface at 100-300.degree. C. for 5-120 seconds to remove
the organic film and to yield an oxide-free copper surface.
6. The process of claim 1, wherein the bifunctional ligand is
dimethylaminoacetonitrile or diethylaminoacetonitrile.
7. A composition comprising: (a) a bifunctional ligand in an
aqueous solution, the bifunctional ligand comprising a nitrile
group and a tertiary amine group attached to a carbon adjacent to
the nitrile group; and (b) sufficient acid so that the pH of the
aqueous solution is between about 2 and about 5.5.
8. A composition comprising: (a) a bifunctional ligand in an
aqueous solution, the bifunctional ligand comprising a moiety
represented by ##STR00003## where R.sup.1 and R.sup.2 are
independently selected from methyl and ethyl; and (b) sufficient
acid so that the pH of the aqueous solution is between about 2 and
about 5.5.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to processes for inhibiting
oxide formation of copper surfaces exposed to air.
BACKGROUND
[0002] The manufacture of ultra-large scale integrated circuits
typically involves a chemical-mechanical planarization (CMP) step
in which a patterned copper surface is subjected to a polishing
process using a combination of abrasives and chemical agents. This
CMP step is typically followed by a post-CMP clean step (pCMP) to
remove residues left by the CMP step from the semiconductor
work-piece surface without significantly etching the metal, leaving
deposits on the surface, or imparting significant organic
carbonaceous contamination to the semiconductor work-piece.
Ideally, the cleaned work-piece proceeds immediately after the pCMP
process into a vacuum environment for the next step of the
manufacturing process. Because of queue time-related delays between
wet and dry tools, work-pieces coming out of pCMP clean do not
always promptly enter a vacuum (air-free) environment for the next
process step, and surface copper oxide formation occurs. This oxide
compromises device performance and must be removed from the copper
surface prior to the deposition of the next layer in the
preparation of copper interconnects on semiconductor chips. In the
dual damascene process, the next layer is typically a silicon
nitride cap layer deposited by plasma enhanced physical vapor
deposition (PECVD).
[0003] The copper oxide layer is currently removed from the copper
surface following pCMP cleaning steps by a plasma clean process.
Although this plasma clean is effective, the exposure of the
dielectric material surrounding the copper lines to the plasma
during the cleaning cycle damages the dielectric material. With the
introduction of more fragile low k dielectric materials in current
and future generations of chips, this damage could be significant
and could change the dielectric properties of the material, leading
to failures.
[0004] In another step in chip fabrication, the semiconductor wafer
is etched to create a pattern of vias and interconnect lines,
followed by cleaning with a post-etch residue (PER) remover to
clean the wafer of any debris resulting from the etching step.
Copper lines exposed during the etching step are susceptible to
copper oxide formation on contact with the ambient atmosphere. As
in the case of pCMP cleaning, any copper oxide formed must be
removed prior to deposition of the next layer, typically a barrier
layer followed by copper layers. Typically, the copper oxide layer
is removed via a plasma clean step that can damage the dielectric
layer.
[0005] Copper surfaces exposed following pCMP cleaning and
post-etch PER removal are susceptible to oxidation owing to the
exposure of the copper surface to the ambient atmosphere.
[0006] A process is needed to prevent the formation of copper oxide
on semiconductor work-pieces that is compatible with chip
manufacturing processes and that does not damage sensitive
dielectric layers.
SUMMARY OF THE INVENTION
[0007] One embodiment is a process comprising contacting a
substantially oxide-free copper surface with an aqueous solution
comprising an acid and a bifunctional ligand for a sufficient
period of time to form a copper surface coated with a layer of the
bifunctional ligand, wherein the bifunctional ligand comprises a
nitrile group and a tertiary amine group attached to a carbon atom
adjacent to the nitrile group, and the pH of the solution is about
2 to about 5.5.
DETAILED DESCRIPTION
[0008] It has been discovered that contacting a substantially
oxide-free copper surface with a bifunctional ligand that contains
both a nitrile group, and a tertiary amine group attached to a
carbon atom of the ligand adjacent to the nitrile group, in an
aqueous solution of pH about 2 to about 5.5, creates a thin layer
of the bifunctional ligand on the copper surface that inhibits the
formation of copper oxides. The bifunctional ligand can be removed
by heating under vacuum to regenerate a substantially oxide-free
copper surface. Typically, the layer, referred to herein as a "thin
layer", of bifunctional ligand is from one monolayer to several
monolayers thick. Preferably, the layer of bifunctional ligand is
from about 5 to about 50 Angstroms thick.
[0009] By "substantially oxide-free" is meant that less than 2 atom
% of the copper surface atoms are coordinated to oxygen. At these
levels, the oxygen atoms are below the X-ray photoelectron
spectroscopy (XPS) detection limit. Substantially oxide-free copper
surfaces can be obtained by processes known in the art such as
treatment with acidic solution, plasma treatment, and
electrochemical reduction.
[0010] In one embodiment, the aqueous solution contains one or more
acids to achieve and maintain the pH between about 2 and about 5.5.
Suitable acids include citric acid, formic acid, acetic acid,
glycolic acid, methanesulfonic acid, oxalic acid, lactic acid,
xylenesulfonic acid, toluenesulfonic acid, tartaric acid, propionic
acid, benzoic acid, ascorbic acid, gluconic acid, malic acid,
malonic acid, succinic acid, gallic acid, butyric acid,
trifluoroacetic acid, glycolic acid, and mixtures thereof. In one
embodiment, the acids are selected from citric acid and glycolic
acid.
[0011] Suitable bifunctional ligands are dialkylaminonitriles that
contain both a nitrile group and a tertiary amine group. Suitable
bifunctional ligands include dimethylaminoacetonitrile and
diethylaminoacetonitrile. These molecules are bifunctional with a
nitrile group and a tertiary amine group attached to a carbon atom
adjacent to the nitrile group. In one embodiment, the bifunctional
ligand is present in an amount of 0.08 to 5 wt %, based on the
total weight of the aqueous solution. In another embodiment, the
bifunctional ligand is present in an amount of 0.1 to 2.5 wt %,
preferably 0.2 to 1 wt %, based on the total weight of the aqueous
solution.
[0012] In one embodiment, the bifunctional ligand comprises a
moiety represented by
##STR00001##
where R.sup.1 and R.sup.2 are independently selected from methyl
and ethyl.
[0013] In one embodiment, the aqueous solution comprises [0014] (a)
a bifunctional ligand comprising a moiety represented by
##STR00002##
[0014] where R.sup.1 and R.sup.2 are independently selected from
methyl and ethyl; and [0015] (b) sufficient acid so that the pH of
the aqueous solution is between about 2 and about 5.5.
[0016] In one embodiment, the aqueous solution contains metal
chelating agents and one or more additives selected from the group
consisting of organic solvents, anticorrosive agents, and
surfactants. Such aqueous solutions can be used as pCMP cleaning
solutions.
[0017] Suitable metal chelating agents include, but are not limited
to, (ethylenedinitrilo)tetraacetic acid (EDTA), terpyridine, citric
acid, gluconic acid, gallic acid, pyrogallol, oximes such as
salicylaldoxime, 8-hydroxyquinoline, polyalkylenepolyamines, crown
ethers, oxalic acid, maleic acid, malonic acid, malic acid,
tartaric acid, aspartic acid, benzoic acid, gluconic acid, glycolic
acid, succinic acid, salts of the aforementioned acids or mixtures
of the acids or their salts, acetylacetone, glycine,
dithiocarbamates, amidoximes, catechol, and cysteine. The metal
chelating agents are typically present in amounts of 500 ppm to 10
wt %, based on the total weight of the aqueous solution. In other
embodiments, the metal chelating agents are present in amounts of 1
to 7.5 wt % or 1.5 to 5 wt %, based on the total weight of the
aqueous solution.
[0018] Suitable organic solvents include alkyl alcohols such as
ethanol and isopropanol. The organic solvents are present in
amounts of 5 to 20 wt %, based on the total weight of the aqueous
solution. In other embodiments, the organic solvents are 1.5 to 12
wt %, or 3 to 10 wt %, based on the total weight of the aqueous
solution.
[0019] Suitable surfactants include cationic, anionic, amphoteric,
and non-ionic surfactants including polyethylene glycols,
polypropylene glycols, fluorosurfactants, polydimethysiloxane
polymers and oligomers, polydimethylsiloxane ethylene oxide and
propylene oxide block co-polymers and oligomers, carboxylic acid
salts, cellulosic surfactants such as hydroxypropylmethylcellulose
and methylcellulose, polyalkylglycolethers, alkyl and aryl sulfonic
acids, polyethyleneglycol alkyl ethers such as Brij.RTM. or
Triton.RTM. surfactants (available from Sigma Aldrich, St. Louis,
Mo.) and phosphate-based surfactants. In one embodiment, the
surfactants are present in amounts of 0.5 to 5 wt %, based on the
total weight of the aqueous solution. In other embodiments, the
surfactants are present in amounts of 0.01 to 0.2 wt %, or 0.02 to
0.1 wt %, based on the total weight of the aqueous solution.
[0020] In another embodiment, the aqueous solution further
comprises one or more additives selected from the group consisting
of corrosion-inhibiting compounds and surface-active agents.
Suitable corrosion-inhibiting compounds include: azoles such as
benzotriazole, 1,2,4-triazole, and imidazole; thiols such as
mercaptoethanol, mercaptopropionic acid, mercaptothiazoline,
mercaptobenzothiazol, and thiolglycerol; and organic reducing
agents such as ascorbic acid, hydroquinone, caffeic acid, glucose,
tannic acid, methoxyphenol, and resorcinol. In one embodiment, the
corrosion-inhibiting compounds are typically present in amounts of
0 ppm to 5 wt %, based on the total weight of the aqueous solution.
In other embodiments, the corrosion-inhibiting compounds are
present in amounts of 0 to 2.5 wt % , or 0 to 1 wt %.
[0021] Suitable bifunctional ligands include
dimethylaminoacetonitrile and diethylaminoacetonitrile. In one
embodiment, the bifunctional ligands are present in amounts of 0.1
to 5 wt %, based on the total weight of the aqueous solution. In
other embodiments, the bifunctional ligands are present in amounts
of 0.1 to 2.5 wt %, or 0.2 to 1 wt %, based on the total weight of
the aqueous solution.
[0022] In another embodiment, the aqueous solution comprises a
bifunctional ligand comprising a metal-coordinating nitrile group
and a tertiary amine group, a fluoride or fluoride equivalent, a
water miscible organic solvent, and an acid comprising one or more
carboxylate moieties, wherein the pH of the solution is about 2 to
about 5.5. Such an aqueous solution is useful as a PER cleaning
solution and can further comprise corrosion-inhibiting agents
and/or phosphonate-containing chelators. Suitable fluorides and
fluoride equivalents include fluoride-containing acids and
metal-free salts thereof. The term "metal-free salt of a
fluoride-containing acid" as used herein means that the salt anion
(or cation) does not contain a metal (e.g., sodium or potassium).
Suitable salts include those formed by combining a
fluoride-containing acid such as hydrogen fluoride,
tetrafluoroboric acid, and/or trifluoroacetic acid, with any of:
ammonium hydroxide; a C1-C4 alkyl quaternary ammonium ion, such as
tetramethylammonium, tetraethylammonium or
trimethyl(2-hydroxyethyl)ammonium; or a primary, secondary or
tertiary amine, such as monoethanolamine,
2-(2-aminoethylamino)ethanol, diethanolamine, 2-ethylaminoethanol
or dimethylaminoethanol. In one embodiment, the fluorides or
fluoride equivalents are typically present in amounts of 0.005 to
0.6 wt %, based on the total weight of the aqueous solution. In
other embodiments, the fluorides or fluoride equivalents are
present in amounts of 0.0175 to 0.043 wt %, or 0.0175 to 0.038 wt
%, based on the total weight of the aqueous solution.
[0023] In one embodiment, the aqueous solution contains one or more
acids to achieve and maintain the pH between about 2 and about 5.5
Preferred organic acids are carboxylic acids, e.g., mono-, di-
and/or tri-carboxylic acids optionally substituted in a beta
position with an hydroxy, carbonyl or amino group. Organic acid
species useful in the composition include but are not limited to
formic acid, acetic acid, propanoic acid, butyric acid and the
like; hydroxy substituted carboxylic acids including but not
limited to glycolic acid, lactic acid, tartaric acid and the like;
oxalic acid; carbonyl substituted carboxylic acids including but
not limited to glyoxylic acid, and the like; amino substituted
carboxylic acids including but not limited to glycine,
hydroxyethylglycine, cysteine, alanine and the like; cyclic
carboxylic acids including but not limited to ascorbic acid and the
like; oxalic acid, nitrilotriacetic acid, citric acid, and mixtures
thereof. Mono- and di-carboxylic acids having between 1 and 8
carbon atoms, preferably between 2 and 6 carbon atoms, and are
substituted in an alpha, beta, or both positions with an hydroxy
and/or carbonyl group, are preferred organic acids. More preferred
are organic acids with a carbonyl group substituted on the carbon
adjacent to the carboxyl group carbon. Exemplary preferred organic
acids are oxalic acid, glyoxylic acid, citric acid, glycolic acid,
or mixtures thereof. In selected embodiments, the organic acids are
present in amounts of 2 to 10 wt %, or 2.7 to 10 wt %, or 2 to 4 wt
%, based on the total weight of the aqueous solution.
[0024] Suitable water-miscible organic solvents include: dimethyl
sulfoxide; ethylene glycol; organic acid alkyl (e.g.,
C.sub.1-C.sub.6) esters, such as ethyl lactate; ethers, such as
ethylene glycol alkyl ether, diethylene glycol alkyl ether
triethylene glycol alkyl ether, propyleneglycol, and propylene
glycol alkyl ether; N-substituted pyrrolidones, such as
N-methyl-2-pyrrolidone; sulfolanes; dimethylacetamide; and any
combination thereof. In one embodiment where a polar organic
solvent is present, the boiling point of the polar organic solvent
is at least about 85.degree. C., alternatively at least about
90.degree. C., or at least about 95.degree. C. In one embodiment,
the water-miscible solvents are present in amounts of 1 wt % to
less than 20 wt %, based on the total weight of the aqueous
solution. In other embodiments, the water-miscible solvents are
present in amounts of 1.5 to 12 wt %, or 3 to 10 wt %, based on the
total weight of the aqueous solution.
[0025] Suitable phosphonate-containing chelators include amino
trimethylphosphonic acid, hydroxyethylidene 1,1-diphosphonic acid,
hexamethylene diamine tetra methylene phosphonic acid,
diethylenetriamine pentamethylene phosphonic acid, bishexamethylen
triamine penta methylene phosphonic acid, and hydroxyethylidene
1,1-diphosphonic acid (DQUEST.RTM. 2010). In one embodiment, the
chelating agent, if present, is present in amounts from about 0.01
to about 5 wt %, based on the total weight of the aqueous solution.
In other embodiments, the chelating agent is present in amounts
from about 0.01 to 0.2 wt %, or 0.02 to 0.1 wt %, based on the
total weight of the aqueous solution. Suitable bifunctional ligands
include dimethylaminoacetonitrile and diethylaminoacetonitrile. In
one embodiment, the bifunctional ligands are present in amounts of
0.1 to 5 wt %, based on the total weight of the aqueous solution.
In other embodiments, the bifunctional ligands are present in
amounts of 0.1 to 2.5 wt %, or 0.2 to 1 wt %, based on the total
weight of the aqueous solution.
[0026] In one embodiment, a substantially oxide-free copper surface
is contacted with an aqueous solution of pH about 2 to about 5.5
that comprises a bifunctional ligand containing both a nitrile
group and a tertiary amine group for a sufficient period of time to
form a copper surface coated with a thin layer of the bifunctional
ligand.
[0027] In a further embodiment, the coated copper surface is rinsed
to remove excess solution and optionally dried.
[0028] In a further embodiment, the coated copper surface is heated
under vacuum at a temperature of 150-300.degree. C. for 5-120
seconds to yield a substantially oxide-free surface with the copper
in the metallic state. Although some surface oxidation (i.e.,
generation of Cu(I) and Cu(II) species) may occur at the copper
surface on exposure to the ambient atmosphere following formation
of the coating, heating the coated surface under vacuum as
described removes the layer of the bifunctional ligand and
generates a substantially oxide-free copper surface. Surface oxide
(e.g., Cu.sub.2O and CuO) is not observed over exposure times up to
72 hours or longer on copper surfaces treated with the bifunctional
ligands. The coating can also be removed with brief plasma
cleaning. The process can prevent deep oxide formation on the
copper surface, as shown by XPS analysis of surfaces.
[0029] Because the thin layer of the bifunctional ligand can be
removed by heating under vacuum or in a reducing (e.g.,
N.sub.2/H.sub.2) plasma, the surface protection and coating removal
steps can be integrated into the PECVD nitride cap step.
[0030] In one embodiment, a dialkylaminonitrile is used to create a
thin layer of the bifunctional ligand on the copper surface during
the pCMP cleaning process. The ligand can be added to the aqueous
pCMP cleaning solution at the start of the cleaning cycle, during
the cleaning cycle, or after the cleaning step. If it is added
after the cleaning step, an aqueous solution with pH between about
2 and about 5.5 that contains the ligand is added to cleaning
solution. Acid is added as needed to adjust and maintain the
solution pH between about 2 and about 5.5. Excess aqueous solution
is removed from the subsequent rinse step.
[0031] In another embodiment, the dialkylaminonitrile is used to
create a thin layer of the bifunctional ligand on the copper
surface during the PER cleaning process. The ligand can be added to
the aqueous PER cleaning solution at the start of the cleaning
cycle, during the cleaning cycle, or after the cleaning step. If it
is added after the cleaning step, an aqueous solution with pH
between about 2 and about 5.5 that contains the ligand is added to
cleaning solution. Acid is added as needed to adjust and maintain
the solution pH between 2 and 5.5. Excess aqueous solution is
removed from the subsequent rinse step.
EXAMPLES
[0032] General: Physical vapor deposited copper on-silicon wafers
were obtained from Sematech. Ion-chromatography grade water from a
Satorius Arium 611DI unit (Sartorius North America Inc., Edgewood,
N.Y.) was used to prepare solutions and rinse glassware prior to
use. Linear sweep voltammetry studies were performed with a
Bioanalytical Systems CV-50W (West Lafayette, Ind.) in 0.1 M sodium
perchlorate solution (Fischer, analytical grade). This reagent was
used as received.
[0033] Citranox from Alconox is a liquid cleaner used to remove
oxide and other contaminants from metal surfaces; it is supplied in
a concentrated form and diluted prior to use.
[0034] X-ray photoelectron spectroscopy (XPS) studies of
chemisorbed precursor were performed using a Physical Electronics
PHI 5800ci spectrometer. The XPS system was under ultra-high vacuum
with base pressure less than .about.5.times.10.sup.-10 torr. The
instrument was operated with an Al monochromatic X-ray source. A
hemi-spherical analyzer was used to collect photoelectrons. A PHI
Model 06-350 ion gun and a Model NU-04 neutralizer were used to
compensate for charging effects. The analytical area was at 0.8-mm
diameter. The escape depth of carbon was .about.65 .ANG. at
45.degree. exit angle. PHI MultiPak@ software version 6.0A was used
for data analysis.
Example 1
[0035] A copper-on-silicon wafer was cleaned of carbonaceous
materials by washing in carbon tetrachloride with sonication,
followed by 2-propanol with sonication. The wafer was rinsed with
ion-chromatography grade water and then cleaned in a 2% Citranox
solution at pH 3 with sonication for 10 minutes at 50.degree. C.
The sample was then thoroughly rinsed with ion-chromatography grade
water saturated with argon. The wafer was then transferred to an
argon-filled glove bag, rinsed with deaerated ion-chromatograph
grade water, allowed to dry under argon flow, and loaded into a
transfer vessel for transport to the X-ray photoelectron
spectrophotometer without exposure to the ambient atmosphere. The
copper surface was analyzed by XPS and shown to be oxide free.
[0036] The above procedure was repeated. After the 10 minutes at
50.degree. C. sonication in a 2% Citranox solution,
dimethylaminoacetonitrile was added to the 2% Citranox solution to
generate a final concentration of 50 mM. The wafer was soaked in
this solution for two minutes at 50.degree. C. The wafer was then
rinsed with ion-chromatography grade water and exposed to the
ambient atmosphere. XPS analysis of the surface after one hour
exposure to the ambient atmosphere showed that the surface copper
atoms are coordinated to nitrogen and that the surface contains
carbonaceous material with oxygen and nitrogen. Surface infrared
red analysis showed a strong nitrile stretch, confirming the
presence of the nitrile on the copper surface. Time-of-flight
secondary ion mass spectrometric data also support the presence of
the thin organic layer. Similar results were obtained at longer
exposures, up to 68 hours.
[0037] Heating the wafer to 200.degree. C. for 1 minute under
vacuum yielded an oxide free copper surface. XPS analysis of this
surface confirms the presence of an oxide-free copper surface.
Example 2
[0038] A copper-on-silicon wafer was cleaned of carbonaceous
materials by washing in carbon tetrachloride with sonication,
followed by 2-propanol with sonication. The wafer was rinsed with
ion-chromatography grade water and then cleaned in a 2% solution of
DuPont EKC 5510; the pH of the solution was adjusted to 3.5 by the
addition of citric acid prior to contact with the wafer. Cleaning
of the copper wafer with this solution was performed by contacting
the wafer with the solution at 50.degree. C. for 8 minutes with
ultrasonic cleaning. Sonication was then discontinued.
Dimethylaminoacetonitrile was then added to bring the solution
concentration to 50 mM, and the wafer was allowed to stand in the
mixture for 2 minutes without ultrasonic agitation at 50.degree. C.
The sample was then rinsed with ion chromatography grade water and
air dried. The sample was exposed to the ambient atmosphere for 68
hours. XPS and linear sweep voltammetric data show the presence of
a Cu-dimethylaminoacetonitrile complex, but no copper oxides.
Heating of the wafer to 200.degree. C. for 5 minutes yielded a
copper surface that was free of oxide contamination as shown by XPS
data.
Example 3
[0039] A copper-on-silicon wafer was cleaned of carbonaceous
materials by washing in carbon tetrachloride with sonication,
followed by 2-propanol with sonication. The wafer was rinsed with
ion-chromatography grade water, and then cleaned in a 2% solution
of DuPont EKC 520 PER cleaner in the following manner. The wafer
was contacted with this solution at 50.degree. C. for 8 minutes
with ultrasonic cleaning. Sonication was then discontinued.
Dimethylaminoacetonitrile was then added to bring the solution
concentration to 50 mM, and the wafer was allowed to stand in the
mixture for 2 minutes without ultrasonic agitation. The sample was
then rinsed with ion chromatography grade water and air dried. The
sample was exposed to the ambient atmosphere for up to 48 hours.
Linear sweep voltammetry showed the presence of a
Cu-dimethylaminoacetonitrile complex, but no reduction waves
associated with Cu(I) and Cu(II) oxides were observed.
Comparative Example A
[0040] A copper foil was cleaned of carbonaceous materials by
washing in carbon tetrachloride with sonication, followed by
2-propanol with sonication. The wafer was rinsed with
ion-chromatography grade water and then cleaned in a 4% solution of
Citranox at pH 3. Cleaning of the copper wafer with this solution
was performed by contacting the wafer with the solution at
50.degree. C. for 8 minutes with ultrasonic cleaning. Sonication
was then discontinued. methylaminoacetonitrile was then added to
bring the solution concentration to 50 mM, and the wafer was
allowed to stand in the mixture for 2 minutes without ultrasonic
agitation at 50.degree. C. The sample was then removed from the
solution, rinsed with ion-chromatography grade water, and exposed
to the ambient atmosphere for one hour. Analysis by linear sweep
voltammetry from -140 mV to -1100 mV (versus Ag/AgCl reference
electrode) showed the presence of copper oxide on the surface.
* * * * *