U.S. patent application number 11/881338 was filed with the patent office on 2007-11-22 for method of polishing a tungsten-containing substrate.
This patent application is currently assigned to Cabot Microelectronics Corporation. Invention is credited to Dinesh N. Khanna, Alexander Simpson, Robert Vacassy.
Application Number | 20070266641 11/881338 |
Document ID | / |
Family ID | 39679434 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070266641 |
Kind Code |
A1 |
Vacassy; Robert ; et
al. |
November 22, 2007 |
Method of polishing a tungsten-containing substrate
Abstract
The invention provides a chemical-mechanical polishing
composition particularly useful in polishing tungsten-containing
substrates. The composition comprises a tungsten etchant, an
inhibitor of tungsten etching, and water, wherein the inhibitor of
tungsten polishing is a polymer, copolymer, or polymer blend
comprising at least one repeating group comprising at least one
nitrogen-containing heterocyclic ring or a tertiary or quaternary
nitrogen atom.
Inventors: |
Vacassy; Robert; (Aurora,
IL) ; Khanna; Dinesh N.; (Naperville, IL) ;
Simpson; Alexander; (Glen Allen, VA) |
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: |
39679434 |
Appl. No.: |
11/881338 |
Filed: |
July 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11670137 |
Feb 1, 2007 |
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11881338 |
Jul 26, 2007 |
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10869397 |
Jun 16, 2004 |
7247567 |
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11670137 |
Feb 1, 2007 |
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Current U.S.
Class: |
51/308 |
Current CPC
Class: |
C09G 1/02 20130101; H01L
21/3212 20130101; C23F 3/06 20130101; C09K 3/1463 20130101 |
Class at
Publication: |
051/308 |
International
Class: |
C09C 1/68 20060101
C09C001/68 |
Claims
1-20. (canceled)
21. A chemical-mechanical polishing composition comprising: (a)
ferric ion, (b) an inhibitor of tungsten etching, wherein the
inhibitor of tungsten etching is a polymer, copolymer, or polymer
blend comprising at least one repeating group comprising at least
one nitrogen-containing heterocyclic ring or a tertiary or
quaternary nitrogen atom, wherein the inhibitor of tungsten etching
is present in an amount of about 1 ppm to about 1000 ppm, (c)
silica, (d) malonic acid, and (e) water.
22. The chemical-mechanical polishing composition of claim 21,
wherein the inhibitor of tungsten etching is a
polyvinylimidazole.
23. The chemical-mechanical polishing composition of claim 22,
wherein the inhibitor of tungsten etching is a
poly(1-vinylimidazole).
24. The chemical-mechanical polishing composition of claim 21,
wherein the inhibitor of tungsten etching is a
dialkylamine-epichlorohydrin copolymer.
25. The chemical-mechanical polishing composition of claim 24,
wherein the inhibitor of tungsten etching is a copolymer of
2,2'-dichlorodiethyl ether and a
bis[.OMEGA.-(N,N-dialkyl)alkyl]urea.
26. The chemical-mechanical polishing composition of claim 21,
wherein the polishing composition further comprises a
per-compound.
27. The chemical-mechanical polishing composition of claim 26,
wherein the per-compound is hydrogen peroxide.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application is a continuation of copending U.S.
patent application Ser. No. 11/670,137, filed Feb. 01, 2007, which
is a continuation-in-part of U.S. patent application Ser. No.
10/869,397, filed Jun. 16, 2004, now issued as U.S. Pat. No.
7,247,567.
FIELD OF THE INVENTION
[0002] This invention pertains to the chemical-mechanical polishing
of substrates comprising tungsten. The invention further provides a
polishing composition comprising ferric ion, a polymer, silica,
malonic acid, and water.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits are made up of millions of active
devices formed in or on a substrate, such as a silicon wafer. The
active devices are chemically and physically connected into a
substrate and are interconnected through the use of multilevel
interconnects to form functional circuits. Typical multilevel
interconnects comprise a first metal layer, an interlevel
dielectric layer, and sometimes a third and subsequent metal layer.
Interlevel dielectrics, such as doped and undoped silicon dioxide
(SiO.sub.2) and/or low-.kappa. dielectrics, are used to
electrically isolate the different metal layers. As each layer is
formed, typically the layer is planarized to enable subsequent
layers to be formed on top of the newly formed layer.
[0004] Tungsten is increasing being used as a conductive material
to form the interconnections in integrated circuit devices. One way
to fabricate planar tungsten circuit traces on a silicon dioxide
substrate is referred to as the damascene process. In accordance
with this process, the silicon dioxide dielectric surface is
patterned by a conventional dry etch process to form holes and
trenches for vertical and horizontal interconnects. The patterned
surface is coated with an adhesion-promoting layer such as titanium
or tantalum and/or a diffusion barrier layer such as titanium
nitride or tantalum nitride. The adhesion-promoting layer and/or
the diffusion barrier layer are then over-coated with a tungsten
layer. Chemical-mechanical polishing is employed to reduce the
thickness of the tungsten over-layer, as well as the thickness of
any adhesion-promoting layer and/or diffusion barrier layer, until
a planar surface that exposes elevated portions of the silicon
dioxide surface is obtained. The vias and trenches remain filled
with electrically conductive tungsten forming the circuit
interconnects.
[0005] Typically, chemical-mechanical polishing compositions for
polishing tungsten-containing substrates comprise compounds capable
of etching tungsten. The compounds capable of etching tungsten, or
etchants, serve to convert tungsten into a soft oxidized film that
is capable of controlled removal by mechanical abrasion. Abrasion
is performed using abrasives suspended in a liquid carrier to form
a polishing slurry in conjunction with a polishing pad or with
abrasives fixed to a polishing pad, in which movement of the
polishing pad relative to the substrate (i.e., a semiconductor
wafer) with the polishing slurry therebetween causes mechanical
removal of the soft oxidized film. However, the etchants often are
capable of converting tungsten metal or its oxide directly into
soluble forms of tungsten. In the polishing step, the over-coating
layer of tungsten is removed to expose the oxide layer and to
achieve planarity of the substrate. After exposure of the oxide
layer and before completion of the polishing process, tungsten in
the trenches undesirably can be eroded by a combination of static
etching and by mechanical action of the abrasives, leading to
dishing and erosion. Dishing may compromise circuit integrity and
leads to surface non-planarity, which may complicate deposition of
metal layers on subsequent levels of the device. Inhibitors of
tungsten etching have been added to chemical-mechanical polishing
compositions. For example, U.S. Pat. No. 6,273,786 discloses a
chemical-mechanical polishing process comprising a tungsten
corrosion inhibitor selected from the group consisting of
phosphates, polyphosphates, silicates, and mixtures thereof. U.S.
Pat. No. 6,083,419 discloses a chemical-mechanical polishing
composition comprising an inhibitor of tungsten etching that is a
compound selected from the group consisting of nitrogen-containing
heterocycles without nitrogen-hydrogen bonds, sulfides, and
oxazolidines.
[0006] However, such inhibitors are not always effective at
preventing erosion of tungsten within trenches. Additionally, use
of high levels of such inhibitors of tungsten etching can reduce
the polishing rates of substrates comprising tungsten layers to
unacceptably low levels. Erosion is a function not only of tungsten
etching, but also of the abrasion process. Thus, there remains a
need in the art for compositions and methods for
chemical-mechanical planarization of tungsten-containing substrates
that will provide for reduced erosion of tungsten and yet maintain
useful rates of tungsten removal. The invention provides such a
chemical-mechanical polishing 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
[0007] The invention provides a method of chemically-mechanically
polishing a substrate comprising tungsten comprising (i) contacting
a substrate comprising tungsten with a polishing pad and a
chemical-mechanical polishing composition comprising (a) a tungsten
etchant, (b) an inhibitor of tungsten etching, where the inhibitor
of tungsten polishing is present in an amount of about 1 ppm to
about 1000 ppm, and (c) water, (ii) moving the polishing pad
relative to the substrate with the polishing composition
therebetween, and (iii) abrading at least a portion of the
substrate to polish the substrate. The inhibitor of tungsten
etching is a polymer, copolymer, or polymer blend comprising at
least one repeating group comprising at least one
nitrogen-containing heterocyclic ring or a tertiary or quaternary
nitrogen atom. The invention further provides a polishing
composition comprising (a) ferric ion, (b) an inhibitor of tungsten
etching, where the inhibitor of tungsten etching is present in an
amount of about I ppm to about 1000 ppm, (c) silica, (d) malonic
acid, and (e) water, wherein the inhibitor of tungsten etching is
as recited above.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The invention is directed to a method of polishing a
substrate comprising tungsten. The method comprises (i) contacting
a substrate comprising tungsten with a polishing pad and a
chemical-mechanical polishing composition comprising (a) a tungsten
etchant, (b) an inhibitor of tungsten etching, wherein the
inhibitor of tungsten etching is present in an amount of about 1
ppm to about 1000 ppm, and (c) water, (ii) moving the polishing pad
relative to the substrate with the polishing composition
therebetween, and (iii) abrading at least a portion of the
substrate to polish the substrate. The inhibitor of tungsten
polishing is a polymer, copolymer, or polymer blend comprising at
least one repeating group comprising at least one
nitrogen-containing heterocyclic ring or a tertiary or quaternary
nitrogen atom. The invention further provides a polishing
composition comprising (a) ferric ion, (b) an inhibitor of tungsten
etching, wherein the inhibitor of tungsten etching is as recited
above, (c) silica, (d) malonic acid, and (e) water.
[0009] The method of the invention can be used to polish any
suitable substrate that comprises tungsten, such as a semiconductor
substrate. Generally, the inventive method is used to polish a
tungsten layer of a substrate. For example, the method of the
invention can be used to polish at least one tungsten metal layer
associated with a substrate selected from the group consisting of
silicon substrates, TFT-LCD (thin film transistor liquid crystal
display) glass substrates, GaAs substrates, and other substrates
associated with integrated circuits, thin films, multiple level
semiconductors, wafers, and the like.
[0010] The chemical-mechanical polishing composition includes a
tungsten etchant. The tungsten etchant can be any suitable compound
or ionic species that etches tungsten. The term "compound or ionic
species that etches tungsten" as used herein refers to a compound
or ionic species that corrodes tungsten by turning solid tungsten
metal into a soluble tungsten corrosion product. A compound or
ionic species that etches tungsten may include one or more
components that react with tungsten metal or its oxide to form
soluble tungsten corrosion products. Generally, the process of
corrosion is an oxidation process, in which electrons are
transferred from solid tungsten metal to the compound or ionic
species that etches tungsten, to form tungsten species with a
higher oxidation state than that of solid tungsten metal or its
oxide.
[0011] Examples of compounds that etch tungsten include but are not
limited to oxidizing agents, fluoride-containing agents, and
organic acids such as oxalic acid and malonic acid. The compound
that etches tungsten desirably comprises at least one metal ion
with a suitable oxidation potential. Preferably, the etchant is
ferric ion, which can be provided by way of any suitable compound
comprising ferric ion, e.g., a compound that disassociates in water
to provide ferric ions, such as ferric nitrate.
[0012] Desirably, the etchant, such as ferric ion, is present in
the chemical-mechanical polishing composition at a concentration of
about 0.0002 M or more (e.g., about 0.001 M or more, or about 0.005
M or more, or about 0.01 M or more). Preferably, the etchant, such
as ferric ion, is present at a concentration of about 0.4 M or less
(e.g., about 0.2 M or less, or about 0.1 M or less).
[0013] The chemical-mechanical polishing composition includes an
inhibitor of tungsten etching. The inhibitor of tungsten etching is
a compound that inhibits the conversion of solid tungsten metal or
its oxide into soluble tungsten compounds while allowing the
composition to convert tungsten into a soft oxidized film that can
be controllably removed by abrasion. Classes of compounds that are
useful as inhibitors of tungsten etching in the context of the
invention include polymers comprising repeating groups comprising
at least one nitrogen-containing heterocyclic ring, and polymers
comprising repeating groups comprising at least one tertiary or
quaternary nitrogen atom. Preferred examples of polymers comprising
at least one nitrogen-containing heterocyclic ring include polymers
comprising imidazole rings. Preferred examples of polymers
comprising a tertiary or quaternary nitrogen atom include
copolymers of alkylated amine monomers and nonionic monomers.
[0014] As used herein, the term imidazole refers to a 5-membered
cyclic structure having two nitrogen atoms and three carbon atoms,
in which the nitrogen atoms are at the 1- and 3-positions on the
ring, and the carbon atoms are at the 2-, 4-, and 5-positions on
the ring.
[0015] The inhibitor of tungsten etching can be any polymer
comprising heterocyclic nitrogen-containing rings. In a first
embodiment, the inhibitor of tungsten etching is a polymer
comprising imidazole rings. The polymer can be a polymer or
copolymer containing only imidazole-containing repeating units, or
can be a copolymer containing one or more imidazole-containing
repeating units in combination with other repeating units,
including but not limited to ethylene, propylene, ethylene oxide,
propylene oxide, styrene, epichlorohydrin, and mixtures thereof.
The copolymer can be a random copolymer, alternating copolymer,
periodic copolymer, block copolymer (e.g., AB, ABA, ABC, etc.),
graft copolymer, or comb copolymer.
[0016] The imidazole rings can be attached at the 1-, 2-, or
4-position of the imidazole ring. When the imidazole ring is
attached to the polymer at the 2- or 4-positions, it is well
appreciated in the art that one of the two ring nitrogen atoms can
bear either a hydrogen atom or another functional group, for
example, alkyl or aryl. When the imidazole ring is optionally
substituted with an alkyl group on a ring nitrogen, the imidazole
ring can be further quaternized, i.e., the alkyl group-substituted
ring nitrogen can be bonded to four carbon atoms and have a
positive charge. Furthermore, the imidazole rings can be further
substituted with additional functional groups at any open position
or can be annelated to a second ring as in, for example,
benzimidazole. In a preferred embodiment, the polymer comprising
imidazole rings is a polymer derived from the polymerization of
1-vinylimidazole, e.g., a poly(1-vinylimidazole).
[0017] In a second embodiment, the inhibitor of tungsten etching
comprises a polymer comprising tertiary or quaternary nitrogen
atoms. The polymer can consist of a single repeating group
comprising tertiary or quaternary nitrogen atoms, or can be a
copolymer containing one or more of such repeating units in
combination with other repeating units, including but not limited
to ethylene, propylene, ethylene oxide, propylene oxide, styrene,
epichlorohydrin, 2,2'-dichloroethyl ether, and mixtures thereof. A
desirable example of a polymer that consists of repeating groups
comprising tertiary or quaternary nitrogen atoms is a polymer of a
diallyldialkylamine salt. Preferably, the inhibitor of tungsten
etching comprises a copolymer containing one or more repeating
groups comprising a tertiary or quaternary nitrogen atom and one or
more nonionic monomers. The copolymer can be a random copolymer,
alternating copolymer, periodic copolymer, block copolymer (e.g.,
AB, ABA, ABC, etc.), graft copolymer, or comb copolymer. The
inhibitor of tungsten etching can be a dialkylamine-epichlorohydrin
copolymer. A preferred example of a dialkylamine-epichlorohydrin
copolymer is poly(dimethylamine-co-epichlorohydrin). The polymer
comprising tertiary or quaternary nitrogen atoms also can be a
copolymer of 2,2'-dichlorodiethyl ether and a
bis[.OMEGA.-(N,N-dialkyl)alkyl]urea. A preferred copolymer
containing one or more repeating groups comprising a tertiary or
quaternary nitrogen atom and one or more nonionic monomers is
poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea].
[0018] The inhibitor of tungsten etching can comprise a polymer
blend of one or more inhibitors of tungsten etching of the
invention. Many methods for blending of polymers are known in the
art. One suitable method is coextrusion of two or more polymers.
Other methods involve batch mixing of polymers. Any suitable method
can be used to produce an inhibitor of tungsten etching that is a
polymer blend.
[0019] The inhibitor of tungsten etching desirably is present in
the chemical-mechanical polishing composition at the point-of-use
in an amount of about 1 ppm or more (e.g., about 5 ppm or more, or
about 10 ppm or more, or about 50 ppm or more). The inhibitor of
tungsten etching desirably is present in the polishing composition
at the point-of-use in an amount of about 1000 ppm or less (e.g.,
about 800 ppm or less, or about 600 ppm or less, or about 400 ppm
or less). As utilized herein, the term "point-of-use" refers to the
point at which the polishing composition is applied to the
substrate surface (e.g., the polishing pad or the substrate surface
itself).
[0020] While not wishing to be bound by any particular theory, it
is believed that the polymeric inhibitor of tungsten etching
interacts with the tungsten metal surface in a manner that permits
conversion of tungsten metal to a soft oxidized film while
inhibiting direct solubilization of tungsten or its oxide, and
further serves to reduce, or substantially reduce, erosion due to
mechanical abrasion of the tungsten metal itself. The polymeric
inhibitor of tungsten etching may serve as a protective film on the
surface of the tungsten metal that modulates mechanical erosion of
tungsten on a substrate during chemical-mechanical polishing of a
substrate.
[0021] The chemical-mechanical polishing composition optionally
comprises an abrasive. The abrasive can be any suitable abrasive,
many of which are well known in the art. A desirable abrasive is a
metal oxide abrasive. Preferably, the abrasive is selected from the
group consisting of alumina, ceria, silica, titania, zirconia, and
mixtures thereof. More preferably, the abrasive is silica. The
silica can be any suitable form of silica. Useful forms of silica
include but are not limited to fumed silica, precipitated, and
condensation-polymerized silica. The abrasive particles useful in
the invention desirably have an average particle size (e.g.,
average particle diameter) of about 20 nm to about 500 nm.
Preferably, the abrasive particles have an average particle size of
about 70 nm to about 300 nm (e.g., about 100 nm to about 200
nm).
[0022] When an abrasive is present in the chemical-mechanical
polishing composition and is suspended in water, any suitable
amount of abrasive can be present in the polishing composition.
Typically about 0.1 wt. % or more (e.g., about 0.2 wt. % or more,
or 0.3 wt. % or more) of abrasive will be present in the polishing
composition. The amount of abrasive in the polishing composition
typically will be about 10 wt. % or less, and more typically will
be about 5 wt. % or less (e.g., about 3 wt. % or less).
[0023] The abrasive particles preferably are colloidally stable.
The term colloid refers to the suspension of abrasive particles in
the liquid carrier. Colloidal stability refers to the maintenance
of that suspension through 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
unagitated for a time of 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 initial 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). More preferably, the value of
[B]-[T]/[C] is less than or equal to 0.3, and most preferably is
less than or equal to 0.1.
[0024] The chemical-mechanical polishing composition optionally
comprises a per-compound. A per-compound (as defined by Hawley's
Condensed Chemical Dictionary) is a compound containing at least
one peroxy group (--O--O--) or a compound containing an element in
its highest oxidation state. Examples of compounds containing at
least one peroxy group include but are not limited to hydrogen
peroxide and its adducts such as urea hydrogen peroxide and
percarbonates, organic peroxides such as benzoyl peroxide,
peracetic acid, di-tert-butyl peroxide, monopersulfates
(SO.sub.5.sup.2-), dipersulfates (S.sub.2O.sub.8.sup.2-), and
sodium peroxide. Preferably, the per compound is hydrogen
peroxide.
[0025] When a per compound is present in the chemical-mechanical
polishing composition, the per compound can be present in any
suitable amount. The per compound preferably comprises about 10 wt.
% or less (e.g., about 8 wt. % or less, or about 6 wt. % or less)
of the composition.
[0026] The chemical-mechanical polishing composition desirably has
a pH that is about 9 or less (e.g., about 8 or less, or about 6 or
less, or about 4 or less). Preferably, the polishing composition
has a pH of about 1 or more. Even more preferably, the polishing
composition has a pH of about 1 to about 4. The polishing
composition optionally comprises pH adjusting agents, for example
nitric acid or potassium hydroxide. The polishing composition
optionally comprises pH buffering systems, for example potassium
hydrogen phthalate. Such pH buffering systems are well known in the
art.
[0027] The chemical-mechanical polishing composition optionally
comprises a stabilizer. It is well known that hydrogen peroxide and
other per compounds are not stable in the presence of many metal
ions without the use of stabilizers. Without the stabilizer, the
metal ion or ions and the per compound may react in a manner that
degrades the per compound over time. The stabilizer may also
interact with the compound that etches tungsten in the compositions
of the invention and reduce the effectiveness of the etchant.
Therefore, the selection of the choice and of the amount of the
stabilizer can be important and can influence the effectiveness of
the polishing composition.
[0028] Useful stabilizers include but are not limited to phosphoric
acid, organic acids (e.g., malonic acid, citric acid, adipic acid,
oxalic acid, phthalic acid, and ethylenediaminetetraacetic acid),
nitriles, and other ligands that are capable of binding to metal
ions and reduce their reactivity towards per compounds. It will be
appreciated that the aforementioned acids can exist in the form of
a salt (e.g., a metal salt, an ammonium salt, or the like), an
acid, or as a partial salt thereof. For example, malonates include
malonic acid, as well as mono- and di-salts thereof. Preferred
stabilizers are selected from the group consisting of malonic acid,
citric acid, adipic acid, oxalic acid, and mixtures thereof. An
especially preferred stabilizer is malonic acid.
[0029] The stabilizer can be present in the chemical-mechanical
polishing composition in any suitable amount. Desirably, the amount
of stabilizer is based on the amount of the tungsten etchant that
is present in the composition. Preferably, the amount of stabilizer
will be about 1 molar equivalent or more (e.g., about 2 molar
equivalents or more). The amount of stabilizer will typically be
less than about 5 molar equivalents.
[0030] The chemical-mechanical 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 and 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), and
polymers, copolymers, and oligomers thereof, and salts thereof.
Suitable surfactants include, for example, anionic surfactants,
cationic surfactants, anionic polyelectrolytes, cationic
polyelectrolytes, nonionic surfactants, amphoteric surfactants,
fluorinated surfactants, mixtures thereof, and the like.
[0031] The chemical-mechanical polishing composition can be
produced by any suitable technique, many of which are known to
those skilled in the art. For example, the tungsten etchant and the
inhibitor of tungsten etching may be combined in water before
applying the polishing composition to a substrate comprising
tungsten or they may be applied separately to a polishing pad or to
a substrate before or during substrate polishing. Generally, the
components of the polishing composition may be prepared by
combining the ingredients 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.).
[0032] For example, the tungsten etchant and the inhibitor of
tungsten etching can be combined in water at predetermined
concentrations and mixed until such components are completely
dissolved. A concentrated dispersion of an abrasive, if used, then
can be added, and the mixture diluted to give the desired
concentration of abrasive in the final polishing composition.
Optionally, a per-compound, a stabilizer, and other additives can
be added to the polishing composition at any time during the
preparation of the polishing composition, e.g., before or after
addition of the tungsten etchant and the inhibitor of tungsten
etching, and before or after adding the abrasive, if an abrasive is
desired, and mixed by any method that is capable of incorporating
the additives into the polishing composition. The mixture can be
filtered, if desired, to remove large particulate contaminants such
as dirt or packaging materials before use.
[0033] The polishing composition can be prepared prior to use, with
one or more components, such as the per-compound, added to the
polishing composition just before use (e.g., within about 1 minute
before use, or within about 5 minutes before use, or within about 1
hour before use, or within about 24 hours before use, or within
about 7 days before use). For example, the inhibitor of tungsten
etching may decompose in the presence of the tungsten etchant or in
the presence of the per compound. In such a situation, the
inhibitor of tungsten etching may be added to the polishing
composition immediately before use (e.g., within about 1 minute
before use, or within about 5 minutes before use, or within about 1
hour before use, or within about 24 hours before use, or within
about 7 days before use).
[0034] The chemical-mechanical polishing composition can be
supplied as a one package system comprising tungsten etchant and an
inhibitor of tungsten etching. Optional components, such as an
abrasive and/or a per-compound, can be placed in a second or third
container. Furthermore, the components in the first or second
container can be in dry form while the components in the
corresponding container can be in the form of an aqueous
dispersion. If the per-compound is a solid, it may be supplied
either in dry form or as an aqueous mixture. The per-compound can
be supplied separately from the other components of the polishing
composition. Other two-container, or three- or more container,
combinations of the components of the polishing composition are
within the knowledge of one of ordinary skill in the art.
[0035] The chemical-mechanical polishing composition preferably
comprises about 0.4 M or less of ferric nitrate or ferric ions,
about 1000 ppm or less of a polymer selected from the group
consisting of polyvinylimidazole, dimethylamine-epichlorohydrin
copolymer, and
poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea],
hydrogen peroxide, silica, and water, wherein the pH is about 1 to
about 6. More preferably, the chemical-mechanical polishing
composition comprises about 0.2 mM to about 0.4 M of ferric ion,
about 1 ppm to about 1000 ppm of a polymer selected from the group
consisting of polyvinylimidazole, dimethylamine-epichlorohydrin
copolymer, and
poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea],
about 0.2 wt. % to about 3 wt. % of silica, about 0.1 wt. % to
about 10 wt. % of hydrogen peroxide, and water. The recited
concentrations of specified components refer to the concentrations
at the point-of-use.
[0036] In the method of chemically-mechanically polishing a
tungsten-containing substrate (such as a semiconductor wafer), the
substrate typically will be pressed against a polishing pad in the
presence of a polishing composition under controlled chemical,
pressure, velocity, and temperature conditions. The relative motion
of the substrate and pad can be circular, elliptical, or linear.
Typically, the relative motion of the substrate and pad is
circular.
[0037] Any suitable polishing pad can be used in the method of the
invention. 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.
[0038] The invention also provides a polishing composition
comprising ferric ion, an inhibitor of tungsten etching, wherein
the inhibitor of tungsten etching is a polymer, copolymer, or
polymer blend comprising at least one repeating group comprising at
least one nitrogen-containing heterocyclic ring or a tertiary or
quaternary nitrogen atom, wherein the inhibitor of tungsten etching
is present at the point of use in an amount of about 1 ppm to about
1000 ppm, silica, malonic acid, and water. The other features of
this polishing composition (e.g., the amount of ferric ion, the
amount of silica, the amount of malonic acid, the pH, and other
suitable additives) are the same as set forth above for the
chemical-mechanical polishing composition useful in the method of
the invention.
[0039] The polishing composition can be used to polish any suitable
substrate, for example, by (a) contacting a substrate with the
chemical-mechanical polishing composition and a polishing pad, (b)
moving the polishing pad relative to the substrate with the
chemical-mechanical polishing composition therebetween, and (c)
abrading at least a part of the substrate to polish the substrate.
The chemical-mechanical polishing composition is especially useful
in the method of the invention described above.
[0040] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLE 1
[0041] This example compares the static etch rates observed when a
polishing composition useful in the inventive method, a composition
comprising imidazole, and a control composition are exposed to a
tungsten-containing substrate.
[0042] Similar planar tungsten wafers were exposed to six different
compositions (Compositions 1A, 1B, 1C, 1D, 1E, and 1F). Each of the
compositions comprised about 0.5 wt. % silica, 0.4143 wt. % of a 10
wt. % aqueous solution of ferric nitrate (i.e., 0.0017 M ferric
nitrate), and about 320 ppm of malonic acid in water, and had a pH
of about 2.3. Composition 1A (control) did not contain any other
components. Compositions 1B, 1C, and 1D (comparative) additionally
contained 100 ppm, 500 ppm, and 1000 ppm of imidazole,
respectively. In contrast, Compositions 1E and 1F (invention)
contained 100 ppm and 125 ppm of polyvinylimidazole,
respectively.
[0043] The planar tungsten wafers were immersed in each of the
compositions at about 43.3.degree. C. for 5 minutes, and the
tungsten static etch rate (in angstroms per minute) was determined
for each of the compositions by measuring the change in wafer
thickness and dividing the change in thickness by 5. The results
are summarized in Table 1. TABLE-US-00001 TABLE 1 Tungsten Etch
Rates Composition Etch Rate (.ANG./min) 1A (control) 255.8 1B
(comparative) 192.2 1C (comparative) 202.4 1D (comparative) 198.9
1E (invention) 161.5 1F (invention) 138.4
[0044] As is apparent from the data set forth in Table 1,
Compositions 1E and 1F containing 100 ppm and 125 ppm of
polyvinylimidazole, respectively, showed reductions in the static
etch rate of about 37% and about 46% respectively as compared to
the control compositions, i.e., Composition 1A. Compositions 1B,
1C, and 1D containing 100 ppm, 500 ppm, and 1000 ppm of imidazole,
respectively, showed reductions in the static etch rate of about
25%, 21%, and 22%, respectively, as compared to the control
composition, i.e., Composition 1A. These results demonstrate that
polishing compositions containing inhibitors of tungsten etching in
accordance with the invention exhibit significantly less static
etching as compared to compositions containing imidazole and the
control composition.
EXAMPLE 2
[0045] This example demonstrates the effect on erosion of patterned
tungsten-containing wafers resulting from addition of the
inhibitors of tungsten etching to a polishing composition in
accordance with the invention.
[0046] Similar substrates comprising tungsten overlaid onto
patterned silicon dioxide coated with a Ti/TiN barrier layer were
used as the test substrates. The width of the trenches within the
pattern was 2 microns, the width of silicon dioxide between
trenches was 2 microns, and the pattern density was 50%. A
commercially available polishing tool was used to polish the
substrates with the compositions. The polishing parameters were as
follows: polishing sub-carrier pressure of 21.5 kPa (3.125 psi),
back pressure of 21.5 kPa (3.125 psi), table speed of 100 rpm,
carrier speed of 55 rpm, ring pressure of 19.0 kPa (2.77 psi),
polishing composition delivery rate of 150 ml/min, and ex-situ pad
conditioning using a IC 1000 K-grooved/Suba IV polishing pad.
[0047] Six different compositions were used to
chemically-mechanically polish the substrates (Compositions 2A, 2B,
2C, 2D, 2E, and 2F). Each of the compositions comprised about 0.5
wt. % silica, 0.4143 wt. % of a 10 wt. % aqueous solution of ferric
nitrate (i.e., 0.0017 M ferric nitrate), and about 320 ppm of
malonic acid in water, and had a pH of about 2.3. Composition 2A
(control) did not contain any other components. Composition 2B
(comparative) additionally contained 100 ppm of imidazole.
Composition 2C (invention) additionally contained 100 ppm of
poly(1-vinylimidazole). Composition 2D (invention) additionally
contained 70 ppm of poly(dimethylamine-co-epichlorohydrin).
Composition 2E (invention) additionally contained 100 ppm of
[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea].
Composition 2F (invention) additionally contained 100 ppm of
poly(diallyldimethylammonium) chloride.
[0048] The substrates were polished at endpoint plus 20%
overpolish. Erosion was determined as the difference in height of
oxide within the pattern and height of oxide outside of the
pattern, using a plane parallel to the surface of the substrate as
a reference. The results are summarized in Table 2. TABLE-US-00002
TABLE 2 Erosion Amounts Composition Erosion (.ANG.) 2A (control)
277.4 2B (comparative) 376.8 2C (invention) -8 2D (invention) 34.6
2E (invention) 91.2 2F (invention) 49
[0049] As is apparent from the data set forth in Table 2,
Composition 2B (comparative) exhibited an approximately 36%
increase in erosion as compared with the control composition, i.e.,
Composition 2A. Composition 2C (invention) exhibited essentially no
erosion. Compositions 2D, 2E, and 2F (invention) exhibited
approximately 87%, 67%, and 82% decreases in erosion, respectively,
as compared to the control composition, i.e., Composition 2A. These
results demonstrate that erosion of a tungsten-containing layer can
be substantially reduced through the use of a polishing composition
in accordance with the invention.
[0050] 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.
[0051] 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.
[0052] 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.
* * * * *