U.S. patent application number 12/075019 was filed with the patent office on 2008-07-03 for cmp method for gold-containing substrates.
This patent application is currently assigned to Cabot Microelectronics Corporation. Invention is credited to Vlasta Brusic, Christopher Thompson, Renjie Zhou.
Application Number | 20080156774 12/075019 |
Document ID | / |
Family ID | 38788879 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080156774 |
Kind Code |
A1 |
Brusic; Vlasta ; et
al. |
July 3, 2008 |
CMP method for gold-containing substrates
Abstract
The invention provides a method of chemically-mechanically
polishing a gold-containing surface of a substrate with a
cyanide-free chemical-mechanical polishing (CMP) composition.
Inventors: |
Brusic; Vlasta; (Geneva,
IL) ; Zhou; Renjie; (Aurora, IL) ; Thompson;
Christopher; (Earlville, IL) |
Correspondence
Address: |
STEVEN WESEMAN;ASSOCIATE GENERAL COUNSEL, I.P.
CABOT MICROELECTRONICS CORPORATION, 870 NORTH COMMONS DRIVE
AURORA
IL
60504
US
|
Assignee: |
Cabot Microelectronics
Corporation
|
Family ID: |
38788879 |
Appl. No.: |
12/075019 |
Filed: |
March 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11444866 |
May 31, 2006 |
7368066 |
|
|
12075019 |
|
|
|
|
Current U.S.
Class: |
216/89 ;
257/E21.304 |
Current CPC
Class: |
C09G 1/02 20130101; C23F
3/04 20130101; H01L 21/3212 20130101 |
Class at
Publication: |
216/89 |
International
Class: |
B44C 1/22 20060101
B44C001/22 |
Claims
1. A method for polishing a gold substrate comprising: (a)
contacting a gold-containing surface of a substrate with a
polishing pad and a cyanide-free CMP composition for a time period
sufficient to oxidize gold on the surface of the substrate, the CMP
composition comprising an abrasive, a gold-oxidizing agent, a
cyanide-free gold-solubilizing agent, and an aqueous carrier; and
(b) causing relative motion between the pad and the surface while
maintaining a portion of the CMP composition in contact with the
surface between the pad and the substrate for a time period
sufficient to abrade the oxidized portion of the surface with the
CMP composition.
2. The method of claim 1 wherein the gold oxidizing agent is
present in the composition at a concentration in the range of about
0.5% to about 6% on a weight basis.
3. The method of claim 1 wherein the CMP composition has a basic pH
and the gold-oxidizing agent comprises a persulfate salt.
4. The method of claim 1 wherein the CMP composition has an acidic
pH and gold-oxidizing agent comprises a halogen.
5. The method of claim 1 wherein the CMP composition has an acidic
pH and the gold-oxidizing agent comprises a reactive admixture of
an oxyhalogen compound and a halide salt.
6. The method of claim 1 wherein the cyanide-free gold-solubilizing
agent is present in the composition at a concentration in the range
of about 0.5% to about 6% on a weight basis.
7. The method of claim 1 wherein the cyanide-free gold-solubilizing
agent comprises a phosphonic acid chelating agent, a salt thereof,
or a combination thereof.
8. The method of claim 1 wherein the CMP composition has a basic
pH, the gold-oxidizing agent comprises ammonium persulfate, and the
cyanide-free gold-solubilizing agent comprises a phosphonic acid
chelating agent, a salt thereof, or a combination thereof.
9. The method of claim 1 wherein the abrasive is present in the
composition at a concentration in the range of about 0.5% to about
3% on a weight basis.
10. The method of claim 1 wherein the abrasive comprises
alpha-alumina.
11. A method for polishing a gold substrate comprising: (a)
contacting a gold-containing surface of a substrate with a
polishing pad and a cyanide-free CMP composition for a time period
sufficient to oxidize gold on the surface of the substrate, the CMP
composition comprising an abrasive, an oxyhalogen compound, a
halide salt, and an aqueous carrier; and (b) causing relative
motion between the pad and the surface while maintaining a portion
of the CMP composition in contact with the surface between the pad
and the substrate for a time period sufficient to abrade the
oxidized portion of the surface with the CMP composition, wherein
the oxyhalogen compound and the halide salt are kept separate from
one another and are admixed just prior to contacting the surface of
the substrate, or are admixed on the surface of the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Application for
patent Ser. No. 11/444,866, filed on May 31, 2006, which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention pertains to a chemical-mechanical polishing
composition and a method for polishing a gold-containing surface of
a substrate using the composition.
BACKGROUND OF THE INVENTION
[0003] Compositions and methods for chemical-mechanical polishing
(CMP) the surface of a substrate are well known in the art.
Polishing compositions (also known as polishing slurries) typically
contain an abrasive material in an aqueous carrier. A surface of a
substrate is abraded to polish the surface by contacting the
surface with a polishing pad and moving the polishing pad relative
to the surface while maintaining a CMP slurry between the pad and
the surface. Typical abrasive materials include silicon dioxide
(silica), cerium oxide (ceria), aluminum oxide (alumina), zirconium
oxide (zirconia), and tin oxide. U.S. Pat. No. 5,527,423, for
example, describes a method for chemically-mechanically polishing a
metal layer by contacting the surface with a polishing slurry
comprising high purity fine metal oxide particles in an aqueous
medium. Alternatively, the abrasive material may be incorporated
into the polishing pad. U.S. Pat. No. 5,489,233 discloses the use
of polishing pads having a surface texture or pattern, and U.S.
Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
[0004] Conventional polishing systems and polishing methods
typically are not entirely satisfactory at planarizing
semiconductor wafers. In particular, polishing compositions and
polishing pads can have less than desirable polishing rates, and
their use in the chemical-mechanical polishing of semiconductor
surfaces can result in poor surface quality.
[0005] The difficulty in creating an effective polishing system for
semiconductor wafers stems from the complexity of the semiconductor
wafer. The performance of a given CMP composition generally will
vary depending on the composition (e.g., type of metal, type of
semiconductor, etc.) of the surface being polished. Semiconductor
wafers are typically composed of a substrate, on which a plurality
of devices has been formed. Integrated circuits are chemically and
physically connected into a substrate by patterning regions in the
substrate and layers on the substrate. To produce an operable
semiconductor wafer and to maximize the yield, performance, and
reliability of the wafer, it is desirable to polish select surfaces
of the wafer without adversely affecting underlying structures or
topography. In fact, various problems in semiconductor fabrication
can occur if the process steps are not performed on wafer surfaces
that are adequately planarized. Because the performance of a
semiconductor wafer is directly associated with the planarity of
its surface, it is crucial to use a polishing composition and
method that results in a high polishing efficiency, uniformity, and
removal rate and leaves a high quality polish with minimal surface
defects.
[0006] Various metals and metal alloys have been used to form
electrical connections between interconnection levels and devices,
including titanium, titanium nitride, aluminum-copper,
aluminum-silicon copper, tungsten, platinum, platinum-tungsten,
platinum-tin, ruthenium, gold, and combinations thereof. Gold
presents a particular challenge in that it is chemically resistant,
making it difficult to remove efficiently through
chemical-mechanical polishing.
[0007] CMP compositions for etching and processing gold surfaces
generally include complexing agents that are highly toxic, such as
cyanides, compounds that generate toxic materials, such as
thiosulfates, which generates hydrogen sulfide, or oxidizers that
are intensely colored, such as I.sub.2/KI, which can interfere with
optical CMP endpoint detectors.
[0008] Accordingly, there is an ongoing need for CMP compositions
and polishing methods that exhibit desirable planarization
efficiency, uniformity, and removal rate during the polishing and
planarization of gold-containing substrates without using highly
toxic or highly colored oxidizers.
[0009] The present invention provides such a composition and
method. These and other advantages of the invention, as well as
additional inventive features, will be apparent from the
description of the invention provided herein.
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention provides an improved, cyanide-free CMP
polishing composition that affords efficient removal of gold
without the use of cyanide-containing reagents. A
chemical-mechanical polishing (CMP) composition of the invention
comprises an abrasive, a gold-oxidizing agent, a cyanide-free
gold-solubilizing agent, and an aqueous carrier. Advantageously,
the CMP compositions of the present invention are colorless or
relatively low in color and are cyanide free.
[0011] The gold-oxidizing agent is preferably a persulfate salt, a
reactive admixture of an oxyhalogen compound and a halide salt, or
a combination thereof. A particularly preferred persulfate salt is
ammonium persulfate. A particularly preferred reactive admixture of
an oxyhalogen compound and a halide salt is a mixture of an iodate
compound and an iodide salt.
[0012] In some preferred embodiments the solubilizing agent
comprises a phosphonic acid chelating agent (e.g.,
amino-tris(methylenephosphonic acid) or
hydroxyethylidene-1,1-diphosphonic acid).
[0013] In embodiments in which the gold-oxidizing agent is a
reactive admixture of an oxyhalogen compound and a halide salt, the
admixture also acts as a cyanide-free gold-solubilizing agent
species formed during CMP. If desired, such CMP compositions can
include a separate solubilizing agent, such as a phosphonic acid
chelating agent, in addition to the admixture of oxyhalogen
compound and halide salt; however, an additional solubilizer is not
required. Preferably, the oxyhalogen compound and the halide salt
are combined with other components of the CMP composition just
prior to contacting the CMP composition with a substrate to be
polished, or are admixed with the other components of the CMP
composition right on the surface of the substrate. Under such
conditions, free halogen is rapidly formed and can immediately
react with gold in the substrate, thus avoiding a build-up of free
halogen, and avoiding potential storage problems that could occur
if the oxyhalogen compound and the halide salt are admixed for a
relatively lengthy period prior to use.
[0014] A chemical-mechanical polishing (CMP) method of the present
invention comprises contacting a gold-containing surface of a
substrate with a polishing pad and a cyanide-free CMP composition
of the invention for a time period sufficient to oxidize gold on
the surface of the substrate. The CMP composition comprises an
abrasive, a gold-oxidizing agent, a cyanide-free gold-solubilizing
agent, and an aqueous carrier. Polishing is effected by causing
relative motion between the pad and the substrate while maintaining
a portion of the CMP composition in contact with the surface
between the pad and the substrate for a time sufficient to abrade a
portion of the surface with the CMP composition. For example, the
pad can be rotated while contacting a rotating platen having a
substrate mounted therein. The CMP composition is fed onto the
surface of the substrate in a manner such that a portion of the CMP
composition contacts the surface of the substrate between the pad
and the substrate.
[0015] When utilized to polish a surface comprising gold, the
compositions and methods of the present invention provide for
efficient removal of gold from the surface of the substrate without
utilizing hazardous cyanide-containing reagents.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The invention provides a cyanide-free chemical-mechanical
polishing composition useful for polishing a gold-containing
surface of a substrate. The CMP compositions of the invention
comprise an abrasive (e.g., alumina), a gold-oxidizing agent, a
cyanide-free gold-solubilizing agent (i.e., a material that is
capable of solubilizing oxidized gold species, e.g., Au(+3) and
Au(+1) species), and an aqueous carrier therefor. The cyanide-free
gold-solubilizing agent and the gold-oxidizing agent can comprise
the same material or different materials. Advantageously, the CMP
compositions of the present invention are cyanide-free, thus
avoiding the waste disposal and toxicity problems associated with
conventional gold CMP compositions.
[0017] Any suitable abrasive can be utilized in the CMP
compositions and methods of the present invention. Preferably, the
abrasive comprises alpha-alumina. In some preferred embodiments the
abrasive comprises a surface-treated alpha-alumina. Surface treated
alpha-alumina are well known in the CMP art and are described, for
example, in U.S. Pat. No. 6,258,137 to Garg et al.
[0018] The abrasive particles desirably have an average particle
size (typically, average particle diameter of the smallest spheres
encompassing the particles) of at least about 10 nm, preferably in
the range of about 10 to about 1000 nm, as determined by light
scattering. More preferably, the abrasive particles have an average
particle size in the range of about 50 to about 500 nm.
[0019] The abrasive can be present in the polishing composition in
any suitable amount. The amount of abrasive present in the
polishing composition typically is at least about 0.001 percent by
weight. The amount of abrasive present in the polishing composition
preferably is about 5 percent by weight or less. More preferably,
the amount of abrasive present in the polishing composition is
about 0.1 to about 3% by weight.
[0020] The abrasive desirably is suspended in the polishing
composition, more specifically in the aqueous carrier portion of
the polishing composition. When the abrasive is suspended in the
aqueous carrier, the abrasive preferably is colloidally stable
(i.e., the particles remain suspended in the carrier for a
prolonged period of time). In the context of this invention, an
abrasive is considered colloidally stable if, when the abrasive is
placed into a 100 mL graduated cylinder and allowed to stand
without agitation for a period of about 2 hours, the difference
between the concentration of particles in the bottom 50 mL of the
graduated cylinder ([B] in terms of g/mL) and the concentration of
particles in the top 50 mL of the graduated cylinder ([T] in terms
of g/mL) divided by the total concentration of particles in the
abrasive composition ([C] in terms of g/mL) is less than or equal
to 0.5 (i.e., ([B]-[T])/[C].ltoreq.0.5). The value of ([B]-[T])/[C]
desirably is less than or equal to 0.3, and preferably is less than
or equal to 0.1.
[0021] The CMP compositions of the invention utilizing a persulfate
salt as the gold-oxidizing agent preferably have a basic pH (e.g.,
a pH in the range of about 8 to about 10). More, preferably, CMP
compositions comprising a persulfate salt an oxidizer have a pH in
the range of about 9 to about 9.5. CMP compositions containing a
halogen or a reactive admixture of an oxyhalogen compound and a
halide salt preferably have an acidic pH (i.e., a pH of about 7 or
less, preferably in the range of about 3 to about 7, most
preferably about 5). The CMP composition optionally comprises one
or more pH adjusting agent, for example, potassium hydroxide,
ammonium hydroxide, alkylammonium hydroxides, and/or nitric acid.
The polishing composition can optionally comprise pH buffering
agents, such as ammonium acetate or disodium citrate. Many such pH
buffering agents are well known in the art.
[0022] Suitable gold-oxidizing agents include, without limitation,
persulfate salts, halogens, reactive admixtures of oxyhalogen
compounds and halide salts, which generate halogens, and a
combination of two or more of the foregoing. Preferably, the
gold-oxidizing agent is present in the composition in an amount in
the range of about 0.5 to about 6% by weight.
[0023] In some preferred embodiments the gold-oxidizing agent is a
persulfate salt such as a monopersulfate salt (i.e.
SO.sub.5.sup.-2) or a dipersulfate salt (i.e.,
S.sub.2O.sub.8.sup.-2). A preferred persulfate salt is ammonium
persulfate, (NH.sub.4).sub.2S.sub.2O.sub.8.sup.-2. Preferably, the
persulfate salt is present in the CMP composition at a
concentration in the range of about 0.5 to about 6 percent by
weight, more preferably about 1 to about 4 percent by weight.
Potassium permanganate can be used, as well, although a separate
surface cleaning step may be necessary to remove manganese dioxide
formed during the gold oxidation process.
[0024] In other preferred embodiments the gold-oxidizing agent is a
reactive admixture comprising an oxyhalogen compound and a halide
salt. Such reactive admixtures typically generate a halogen e.g.,
I.sub.2, Br.sub.2, and or Cl.sub.2) in situ, which is capable of
oxidizing gold under the conditions utilized in chemical mechanical
polishing of gold-containing substrates such as integrated circuit
chips, and the like. Examples of suitable oxyhalogen compounds
include iodate compounds such as potassium iodate (KIO.sub.3) or
potassium hydrogen iodate (a 1:1 mixture of HIO.sub.3 acid and
KIO.sub.3), bromate (BrO.sub.3.sup.-1) compounds, chlorate
(ClO.sub.3.sup.-1) compounds, and the like. Preferably, the halogen
salt in the admixture is chosen to complement the oxyhalogen
component (i.e., to include the same halogen atom). For example, an
iodide preferably is utilized in combination with an iodate
compound, a bromide preferably is utilized in combination with a
bromate compound, and a chloride preferably is utilized in
combination with a chlorate compound. Preferably, the oxyhalogen
compound is present in the CMP composition at a concentration in
the range of about 0.5 to about 6 percent by weight (e.g., about 2
percent by weight). The halide preferably is present in the CMP
composition at a concentration in the range of about 1 to about 2
percent by weight.
[0025] Cyanide-free gold-solubilizing agents useful in the
compositions and methods of the present invention include any
chemical compound or combination of compounds that can solubilize
oxidized gold species, e.g. gold(+3). Non-limiting examples of
suitable cyanide-free gold-solubilizing agents include phosphonic
acid chelating agents, admixtures of an oxyhalogen compound and a
halide salt, acetonitrile, ammonium sulfamate, ammonium sulfite,
diethylenetriaminepentaacetic acid and salts thereof, a combination
of two or more of the foregoing, and the like.
[0026] Non-limiting examples of suitable phosphonic acid chelating
agents include, without limitation amino-tris(methylenephosphonic
acid) and hydroxyethylidene-1,1-diphosphonic acid,
hexamethylenediaminetetra(methylenephosphonic acid),
diethylenetriaminepenta(methylenephosphonic acid), salts thereof,
and combinations of two or more of the foregoing thereof.
[0027] The cyanide-free gold-solubilizing agent preferably is
present in the CMP compositions of the present invention in an
amount in the range of about 0.5 to about 6 percent by weight, more
preferably in the range of about 1 to about 4 percent by
weight.
[0028] When a reactive admixture of an oxyhalogen compound (e.g.,
iodate) and a halide salt (e.g., iodide) is utilized as the
gold-oxidizing agent, the halide salt can also act as a
solubilizing agent for oxidized gold species. Thus, in embodiments
utilizing a reactive admixture of an oxyhalogen compound and a
halide salt, an additional solubilizing agent can be omitted, if
desired.
[0029] The aqueous carrier in the CMP compositions of the present
invention can be water (e.g., deionized water), or a mixture of
water with one or more water-soluble solvent such as a lower alkyl
alcohol (e.g., methanol or ethanol), a polyol (e.g., ethylene
glycol or glycerin), and the like. Preferably, the aqueous carrier
is deionized water.
[0030] The polishing composition optionally further comprises one
or more other additives. Such additives include any suitable
surfactant and/or rheological control agent, including viscosity
enhancing agents, coagulants (e.g., polymeric rheological control
agents, such as, for example, urethane polymers), acrylates
comprising one or more acrylic subunits (e.g., vinyl acrylates and
styrene acrylates), polymers, copolymers, and oligomers thereof,
and salts thereof. Suitable surfactants include, for example,
cationic surfactants, anionic surfactants, anionic
polyelectrolytes, nonionic surfactants, amphoteric surfactants,
fluorinated surfactants, mixtures thereof, and the like.
[0031] The polishing composition optionally can further comprise a
biocide. The biocide can be any suitable biocide, for example an
isothiazolinone biocide. The amount of biocide used in the
polishing composition typically is about 1 ppm to about 500 ppm,
and preferably is about 10 ppm to about 200 ppm.
[0032] The polishing composition can be prepared by any suitable
technique, many of which are known to those skilled in the art. The
polishing composition can be prepared in a batch or continuous
process. Generally, the polishing composition can be prepared by
combining the components thereof in any order. The term "component"
as used herein includes individual ingredients (e.g., acids, bases,
etc.) as well as any combination of ingredients (e.g., acids,
bases, surfactants, etc.).
[0033] For example, the abrasive can be dispersed in an aqueous
solvent, such as deionized water. The gold-oxidizing agent and the
solubilizing agent, as well as any other optional component, can
then be added, and mixed by any method that is capable of
incorporating the components into the polishing composition. The
CMP composition can be prepared prior to use, with one or more
components, such as the solubilizing agent or gold-oxidizing agent,
added to the CMP composition just before use (e.g., within about 1
minute before use, or within about 1 hour before use, or within
about 7 days before use). The pH can be adjusted at any suitable
time. The CMP composition also can be prepared by mixing the
components at the surface of the substrate during the polishing
operation.
[0034] The CMP composition also can be provided as a concentrate
which is intended to be diluted with an appropriate amount of water
prior to use. In such an embodiment, the polishing composition
concentrate can comprise an abrasive, a gold-oxidizing agent, a
solubilizing agent, and an aqueous carrier in amounts such that,
upon dilution of the concentrate with an appropriate amount of
aqueous solvent, each component of the polishing composition will
be present in the polishing composition in a suitable effective
amount.
[0035] The invention further provides a method of
chemically-mechanically polishing a gold-containing surface of a
substrate. The present method utilizes a CMP composition of the
present invention (i.e., a CMP composition the CMP composition
comprising an abrasive, a gold-oxidizing agent, a cyanide-free
gold-solubilizing agent, and an aqueous carrier) The method
comprises the steps of (a) contacting a gold-containing surface of
a substrate with a polishing pad and a cyanide-free CMP composition
of the invention for a time period sufficient to oxidize gold on
the surface of the substrate; and (b) causing relative motion
between the pad and the surface while maintaining a portion of the
CMP composition in contact with the surface between the pad and the
substrate for a time sufficient to abrade the oxidized portion of
the surface with the CMP composition.
[0036] The method of the present invention can be used to polish
any suitable substrate, and is especially useful for polishing
surfaces of substrates comprising gold.
[0037] When the gold-oxidizing agent in the CMP composition of the
invention is a reactive admixture of oxyhalogen compound and a
halide salt it is desirable to keep these two materials separate
until just prior to use. Accordingly, when the CMP composition
comprises an oxyhalogen compound, (e.g., potassium iodate,
potassium hydrogen iodate, and the like) and a halide salt, it is
preferred that the oxyhalogen compound and the halide salt are kept
separate from one another and are only admixed just prior to
contacting the surface of the substrate, or are admixed on the
surface of the substrate, itself. The abrasive component of the CMP
composition can be included in either or both of the separate
formulated products. Upon mixing of the two compositions, free
halogen is formed, which then reacts with gold present in the
substrate.
[0038] The CMP method of the invention is particularly suited for
use in conjunction with a CMP apparatus in which a polishing pad
and platen are in relative motion to one another. Typically, the
CMP apparatus comprises a platen, which, when in use, is in motion
and has a velocity that results from orbital, linear, or circular
motion, a polishing pad in contact with the platen and moving with
the platen when in motion, and a carrier attached to the platen,
which holds a substrate to be polished so that it can be contacted
with the polishing pad. A CMP composition is supplied to the
surface to be polished with at least a portion of the CMP
composition being disposed between the substrate and the pad. The
platen, with its affixed substrate, is moved relative to the
surface of the polishing pad for a time period sufficient for the
CMP composition between the substrate and the pad to abrade at
least a portion of the surface of the substrate.
[0039] A substrate can be planarized or polished with the
chemical-mechanical polishing composition with any suitable
polishing pad (e.g., polishing surface). Suitable polishing pads
include, for example, woven and non-woven polishing pads. Moreover,
suitable polishing pads can comprise any suitable polymer of
varying density, hardness, thickness, compressibility, ability to
rebound upon compression, and compression modulus. Suitable
polymers include, for example, polyvinylchloride,
polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester,
polyacrylate, polyether, polyethylene, polyamide, polyurethane,
polystyrene, polypropylene, coformed products thereof, and mixtures
thereof.
[0040] Desirably, the CMP apparatus further comprises an in situ
polishing endpoint detection system, many of which are known in the
art. Techniques for inspecting and monitoring the polishing process
by analyzing light or other radiation reflected from a surface of
the workpiece are known in the art. Such methods are described, for
example, in U.S. Pat. No. 5,196,353, U.S. Pat. No. 5,433,651, U.S.
Pat. No. 5,609,511, U.S. Pat. No. 5,643,046, U.S. Pat. No.
5,658,183, U.S. Pat. No. 5,730,642, U.S. Pat. No. 5,838,447, U.S.
Pat. No. 5,872,633, U.S. Pat. No. 5,893,796, U.S. Pat. No.
5,949,927, and U.S. Pat. No. 5,964,643. Desirably, the inspection
or monitoring of the progress of the polishing process with respect
to a workpiece being polished enables the determination of the
polishing end-point, i.e., the determination of when to terminate
the polishing process with respect to a particular workpiece.
[0041] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLE 1
[0042] This example shows the effect of varying amounts of a
phosphonic acid chelating agent on oxidation and solubilization of
gold utilizing electrochemical techniques.
[0043] The electrochemical apparatus utilized to evaluate the
effects of phosphonic acid chelating agents on the oxidation and
solubilization of gold is similar to one normally used in
evaluation of metallic corrosion. The apparatus included a three
electrode cell, a Princeton Applied Research 273A potentiostat
(along with software for electrochemically evaluating corrosion),
and a Pine rotator. The electrode cell included a gold electrode
(i.e., the working electrode), a platinum counter electrode, and
mercurous surface electrode (MSE) as a reference electrode, and an
abrasive pad at its bottom. The cell was placed on a scale to
select and monitor a down-force used in the tests. Electrochemical
data pertinent to metal dissolution was obtained with a rotating
electrode pressed against the abrasive pad (with a selected down
force), and also with electrode lifted from the pad, i.e., with and
after surface abrasion. The data obtained with abrasion are similar
to the electrochemical metal dissolution observed during polishing,
while the results obtained after abrasion mimic the reactions that
occur in valleys of a semiconductor wafer pattern, where abrasion
does not play a role. The rates of gold dissolution were evaluated
with potentiodynamic potential curves. The potential was varied
about 250 mV below the open circuit potential to some value well
above that potential, with and without abrasion, for aqueous
solutions having a pH of about 9, and containing about 2% ammonium
persulfate and about 0.5, 1, 2, and 4%
1-hydroxyethylidene-1,1-diphosphonic acid (DEQUEST.RTM. 2010).
Differences between data with and without abrasion readily
indicated the extent to which the CMP composition is capable of
metal passivation and re-passivation.
[0044] The gold dissolution rate for each solution was evaluated
from the potentiodynamic curves, which were obtained by varying
potential and recording current generated by all the reactions on
gold. Data with abrasion were obtained with a down force of
approximately 2 psi in solutions without an added abrasive (with
the abrasive pad providing the needed surface abrasion). The
results indicate that additions of a phosphonic acid chelating
agent can greatly diminish the passivating properties of the oxide
film. The calculated gold dissolution rate was determined to be
about 210 .ANG./min with abrasion and 35 .ANG./min after abrasion
was terminated. The dissolution rates obtained at a potential of
0.2 V relative to MSE at each phosphonate level are recorded in
Table 1. The results indicated that in the absence of phosphonate,
the dissolution rate for 2% ammonium persulfate was limited to
about 200 .ANG./min for a downforce of 2 psi or less, while
increasing the phosphonate concentration resulted in an increase in
the gold dissolution rate at the concentrations examined.
TABLE-US-00001 TABLE 1 Effect of varying phosphonate concentration
on gold dissolution rate at a constant 2% ammonium persulfate
concentration. Phosphonate Concentration (wt %) Gold Dissolution
Rate (.ANG./min)* 0% 210 0.5% 212 1% 375 2% 630 4% 1230 *Gold
Dissolution Rate (.ANG./min) measured at about 0.1 V above the open
circuit potential.
EXAMPLE 2
[0045] This example shows the effect of varying the concentration
ammonium persulfate on oxidation and solubilization of gold
utilizing electrochemical techniques.
[0046] The rates of dissolution of gold substrates were monitored
electrochemically in solutions having a pH of about 9 and
containing about 2% by weight of
1-hydroxyethylidene-1,1-diphosphonic acid (DEQUEST.RTM. 2010), and
varying concentrations of ammonium persulfate, in water. An
abrasive pad applied with down-force of about 2 psi was used to
abrade the surface in each evaluation. The ammonium persulfate
concentration was varied from about 1% to about 4% by weight (i.e.,
1%, 2%, and 4%). The gold dissolution rate for each solution was
assessed from potentiodynamic polarization curves by extrapolation
of the anodic and cathodic currents to the open circuit potential.
The calculated dissolution rates for each phosphonate concentration
are recorded in Table 2.
TABLE-US-00002 TABLE 2 Effect of varying persulfate concentration
on gold dissolution rate at a constant 2% phosphonic acid chelating
agent concentration. Ammonium Persulfate Concentration (wt %) Gold
Dissolution Rate (.ANG./min) 1% 38 2% 116 4% 273
EXAMPLE 3
[0047] This Example demonstrates the effect of varying the pH level
on gold dissolution rates, evaluated by electrochemical
techniques.
[0048] The rates of dissolution of gold substrates were monitored
electrochemically in solutions of varying pH containing about 2% by
weight of 1-hydroxyethylidene-1,1-diphosphonic acid (DEQUEST.RTM.
2010) and about 4% by weight of ammonium persulfate, in water. An
abrasive pad applied with down-force of about 2 psi was used to
abrade the surface in each evaluation. The pH was varied from about
2 to about 9 (i.e., 2, 5, 8, and 9). The gold dissolution rate for
each solution was assessed from potentiodynamic polarization curves
by extrapolation of the anodic and cathodic currents to the open
circuit potential. The dissolution rates observed at each pH value
are recorded in Table 3. Use of amino-tris(methylenephosphonic acid
(DEQUEST.RTM. 2000) in place of DEQUEST.RTM. 2010 afforded almost
identical results.
TABLE-US-00003 TABLE 3 Effect of varying pH on gold dissolution
rate at a constant 2% phosphonic acid chelating agent concentration
and 4% ammonium persulfate concentration. pH Gold Dissolution Rate
(.ANG./min) 2 1.5 5 2.1 8 25 9 252
EXAMPLE 4
[0049] This Example demonstrates the effectiveness of CMP
compositions of the invention comprising ammonium persulfate,
alumina, and a phosphonic acid cheating agent for removing gold in
a small scale CMP polishing apparatus.
[0050] The removal rates of gold-containing substrates were
monitored on a small scale polisher for CMP compositions having a
pH of about 9 and containing varying levels of phosphonic acid
chelating agent, ammonium persulfate, and alpha-alumina, in water.
A hard polishing pad applied with down-force of about 2 psi, a
platen rotation speed of about 50 rpm, a carrier rotation speed of
about 53 rpm, and a slurry supply rate of about 200 mL/min was used
to polish the gold surface of each substrate. The substrate was a
Si wafer on which a 340 .ANG. thin layer of titanium was deposited,
followed by a 1600 .ANG. thick layer of gold. The concentration of
1-hydroxyethylidene-1,1-diphosphonic acid (DEQUEST.RTM. 2010) was
varied from about 0.5 to about 2.5% by weight, the amount of
surface-treated alpha alumina was varied from about 1 to about 2%
by weight, and ammonium persulfate was varied from about 2 to about
4% by weight. The gold removal rate in .ANG./min was determined for
each composition. The observed gold removal rates and compositions
are recorded in Table 4. The data clearly indicate that gold
removal rates increases with the % of phosphonic acid chelating
agent, as well as with the increasing levels of the oxidizing agent
and abrasive. The removal rate also increased with increasing
applied down force and increased platen speed.
TABLE-US-00004 TABLE 4 CMP compositions and gold removal rates
obtained therewith. Wt % Wt % Wt % Gold Removal Rate Alumina
(NH.sub.4).sub.2S.sub.2O.sub.8 Phosphonate (.ANG./min) 1.5 3 2 952
1 2 1.5 686 1 2 2.5 962 2 2 2.5 1037 2 4 2.5 1253 2 2 1.5 706 1 4
1.5 878 2 4 1.5 859 1 4 2.5 1154 1.5 3 2 950
EXAMPLE 5
[0051] This Example demonstrates the effectiveness of a CMP
composition of the invention comprising alumina and a reactive
admixture of an iodate compound and iodide for oxidizing an
solubilizing gold.
[0052] The gold removal rates of gold-containing substrates were
monitored on a small scale polisher using a CMP compositions of the
invention having a pH of about 5 to about 7 and containing about 2%
by weight surface-treated alumina (i.e., surface treated with a
polymer), and a reactive admixture containing about 2% by weight
potassium hydrogen iodate and 2% by weight potassium iodide, in
water. The CMP composition was applied to the platen in two parts
(i.e., one containing potassium hydrogen iodate and alumina, and
the other containing potassium iodide and alumina), each part
having the 2.times. concentration of the final composition and
mixed on the platen in approximately 1:1 ratio to obtain the final
composition described above. A hard polishing pad applied with
down-force of about 2 psi, a platen rotation speed of about 50 rpm,
a carrier rotation speed of about 53 rpm, and a slurry supply rate
of about 200 mL/min was used to abrade the gold surface of the
substrate. The gold substrate was a Si wafer having a 100 .ANG.
tantalum layer, a 100 .ANG. platinum layer and a 4000 .ANG. gold
layer deposited thereon. The observed gold removal rate was about
1800 .ANG./min.
[0053] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0054] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0055] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *