U.S. patent application number 11/287039 was filed with the patent office on 2007-05-24 for friction reducing aid for cmp.
This patent application is currently assigned to Cabot Microelectronics Corporation. Invention is credited to Phillip W. Carter, Kevin J. Moeggenborg.
Application Number | 20070117497 11/287039 |
Document ID | / |
Family ID | 38054171 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070117497 |
Kind Code |
A1 |
Moeggenborg; Kevin J. ; et
al. |
May 24, 2007 |
Friction reducing aid for CMP
Abstract
The invention provides a chemical-mechanical polishing system
for polishing a substrate comprising a polishing component, a
water-soluble silicate compound, an oxidizing agent, and water,
wherein the pH of the polishing system is about 8 to about 12. The
invention further provides a method of chemically-mechanically
polishing a substrate with the aforementioned polishing system. The
polishing system provides for reduced friction during polishing of
substrates.
Inventors: |
Moeggenborg; Kevin J.;
(Naperville, IL) ; Carter; Phillip W.;
(Naperville, 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
Aurora
IL
|
Family ID: |
38054171 |
Appl. No.: |
11/287039 |
Filed: |
November 22, 2005 |
Current U.S.
Class: |
451/41 ;
451/285 |
Current CPC
Class: |
B24B 37/0056 20130101;
B24B 57/02 20130101; B24B 37/042 20130101 |
Class at
Publication: |
451/041 ;
451/285 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24B 29/00 20060101 B24B029/00 |
Claims
1. A chemical-mechanical polishing system for polishing a substrate
comprising: (a) a polishing component selected from the group
consisting of a polishing pad, an abrasive, and a combination
thereof, (b) a water-soluble silicate compound in an amount
sufficient to provide about 0.1 wt. % or more of SiO.sub.2, (c) an
oxidizing agent that oxidizes at least part of a substrate, and (d)
water, wherein the pH of the polishing system is about 8 to about
12, and wherein the water-soluble silicate compound is present in
aqueous solution in the polishing system.
2. The polishing system of claim 1, wherein the water-soluble
silicate compound is selected from the group consisting of
potassium silicate, sodium silicate, potassium metasilicate, and
sodium metasilicate.
3. The polishing system of claim 2, wherein the water-soluble
silicate compound is potassium silicate.
4. The polishing system of claim 3, wherein the potassium silicate
is present in an amount sufficient to provide about 0.25 wt. % or
more of SiO.sub.2.
5. The polishing system of claim 3, wherein the potassium silicate
has a SiO.sub.2:K.sub.2O molar ratio of about 2.8 to about 3.9.
6. The polishing system of claim 5, wherein the potassium silicate
has a SiO.sub.2:K.sub.2O molar ratio of about 3 to about 3.6.
7. The polishing system of claim 1, wherein the oxidizing agent is
selected from the group consisting of hydrogen peroxide, iodates,
permanganates, persulfates, hydrogen peroxymonosulfate sulfates,
molybdates, ferric nitrate, nitrates, quinones, and combinations
thereof.
8. The polishing system of claim 1, wherein the polishing system
further comprises an abrasive wherein the abrasive is suspended in
the water.
9. The polishing system of claim 8, wherein the abrasive is
selected from the group consisting of alumina, ceria, silica,
zirconia, and combinations thereof.
10. The polishing system of claim 1, wherein the polishing system
comprises a polishing pad and an abrasive wherein the abrasive is
fixed to the polishing pad.
11. The polishing system of claim 1, wherein the water-soluble
silicate compound is present in an amount of about 0.5 wt. % or
more.
12. The polishing system of claim 1, wherein the pH is about 9 to
about 11.
13. A method of chemically-mechanically polishing a substrate,
which method comprises: (i) contacting a substrate with a
chemical-mechanical polishing system comprising: (a) a polishing
component selected from the group consisting of a polishing pad, an
abrasive, and a combination thereof, (b) a water-soluble silicate
compound in an amount sufficient to provide about 0.1 wt. % or more
of SiO.sub.2, (c) an oxidizing agent that oxidizes at least part of
a substrate, and (d) water, wherein the pH of the polishing system
is about 8 to about 12, and wherein the water-soluble silicate
compound is present in aqueous solution in the polishing system,
and (ii) abrading at least a portion of the substrate to polish the
substrate.
14. The method of claim 13, wherein the water-soluble silicate
compound is selected from the group consisting of potassium
silicate, sodium silicate, potassium metasilicate, and sodium
metasilicate.
15. The method of claim 14, wherein the water-soluble silicate
compound is potassium silicate.
16. The method of claim 15, wherein the potassium silicate is
present in an amount sufficient to provide about 0.25 wt. % or more
of SiO.sub.2.
17. The method of claim 15, wherein the potassium silicate has a
SiO.sub.2:K.sub.2O molar ratio of about 2.8 to about 3.9.
18. The method of claim 17, wherein the potassium silicate has a
SiO.sub.2:K.sub.2O molar ratio of about 3 to about 3.6.
19. The method of claim 13, wherein the oxidizing agent is selected
from the group consisting of hydrogen peroxide, iodates,
permanganates, persulfates, hydrogen peroxymonosulfate sulfates,
molybdates, ferric nitrate, nitrates, quinones, and combinations
thereof.
20. The method of claim 13, wherein the polishing system further
comprises an abrasive wherein the abrasive is suspended in the
water.
21. The method of claim 20, wherein the abrasive is selected from
the group consisting of alumina, ceria, silica, zirconia, and
combinations thereof.
22. The method of claim 13, wherein the polishing system comprises
a polishing pad and an abrasive wherein the abrasive is fixed to
the polishing pad.
23. The method of claim 13, wherein the water-soluble silicate
compound is present in an amount of about 0.5 wt. % or more.
24. The method of claim 13, wherein the pH is about 9 to about
11.
25. The method of claim 13, wherein the substrate comprises a metal
layer.
26. The method of claim 25, wherein the metal layer comprises
tantalum.
27. The method of claim 26, wherein the metal layer further
comprises copper.
28. The method of claim 13, wherein the substrate comprises a
dielectric layer which has a dielectric constant of about 3.5 or
lower.
29. The method of claim 28, wherein the dielectric layer is an
organically modified silicon glass.
30. The method of claim 28, wherein the dielectric layer is
carbon-doped silicon dioxide.
31. The method of claim 28, wherein the substrate further comprises
a metal layer.
32. The method of claim 31, wherein the metal layer comprises
tantalum.
33. The method of claim 32, wherein the metal layer further
comprises copper.
Description
BACKGROUND OF THE INVENTION
[0001] 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. In one manufacturing
process, a dielectric substrate is patterned by a conventional dry
etch process to form holes and trenches for vertical and horizontal
interconnects. The patterned surface is then optionally coated with
a diffusion barrier layer and/or an adhesion-promoting layer,
followed by deposition of a metal layer to fill the trenches and
holes. Chemical-mechanical polishing (CMP) is then employed to
reduce the thickness of the metal layer, as well as the thickness
of the diffusion barrier layer and/or adhesion-promoting layer,
until the underlying dielectric layer is exposed, thus forming the
circuit device.
[0002] In chemical-mechanical polishing, the surface of the
substrate is contacted with a polishing composition and a polishing
component, such as a polishing pad. Polishing compositions (also
known as polishing slurries) typically contain an abrasive material
in an aqueous solution and are applied to a surface by contacting
the surface with a polishing pad saturated with the polishing
composition. Chemical components of the polishing compositions are
thought to react with surface materials of the substrate being
polished, either by converting the surface materials to softer,
more easily abradable derivatives of the materials, which
derivatives are then removed by mechanical action of the abrasive
material and/or the polishing pad, or by solubilizing the surface
materials that are removed by mechanical action alone. In certain
applications, the abrasive can be affixed to the surface of the
polishing pad.
[0003] The frictional forces resulting from the relative motion of
the substrate surface and the surface of the polishing pad with a
polishing composition therebetween during the polishing process can
lead to defectivity of the device being formed on the substrate via
damage of the lines by scratching of the substrate by abrasive
particles and/or the polishing pad and via delamination of the
surface layers from the substrate. In addition, frictional heating
of the polishing pad at the pad/slurry interface can lead to
premature pad failure. Strategies to reduce frictional forces, such
as incorporation of surfactants into polishing compositions, use of
polishing pads composed of softer materials, or reduction of force
applied to the substrate/polishing pad interface often result in
the reduction of removal rates of the materials being polished,
which can result in increased processing times, thus reducing
throughput and increasing overall unit costs.
[0004] Further, in efforts to reduce the capacitance between
conductive layers on microelectronic devices and thus to increase
the frequency or speed at which the devices can operate, materials
having lower dielectric constants than the commonly used silicon
dioxide-based dielectrics are being employed to provide electrical
isolation between circuit lines. Examples of low dielectric
constant materials typically include organic polymer materials,
inorganic and organic porous dielectric materials, and blended or
composite organic and inorganic materials, which can be porous or
non-porous. Such materials are mechanically softer than silicon
dioxide-based dielectrics and are more easily damaged during device
manufacture. It would be highly desirable to incorporate low
dielectric constant materials into semiconductor structures while
still being able to utilize the conventional chemical-mechanical
polishing (CMP) systems for polishing the surface of the resulting
devices during semiconductor wafer processing.
[0005] Thus, a need remains for chemical-mechanical polishing
compositions and systems exhibiting reduced friction between
substrates and polishing components. 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
[0006] The invention provides a chemical-mechanical polishing
system for polishing a substrate comprising (a) a polishing
component selected from the group consisting of a polishing pad, an
abrasive, and a combination thereof, (b) a water-soluble silicate
compound in an amount sufficient to provide about 0.1 wt. % or more
of SiO.sub.2, (c) an oxidizing agent that oxidizes at least part of
a substrate, and (d) water, wherein the pH of the polishing system
is about 8 to about 12. The invention further provides a method of
chemically-mechanically polishing a substrate, which method
comprises (i) contacting a substrate with a chemical-mechanical
polishing system comprising (a) a polishing component selected from
the group consisting of a polishing pad, an abrasive, and a
combination thereof, (b) a water-soluble silicate compound in an
amount sufficient to provide about 0.1 wt. % or more of SiO.sub.2,
(c) an oxidizing agent that oxidizes at least part of a substrate,
and (d) water, and (ii) abrading at least a portion of the
substrate to polish the substrate, wherein the pH of the polishing
system is about 8 to about 12.
BRIEF DESCRIPTION OF THE DRAWING
[0007] The Figure illustrates a method for determination of the
coefficient of friction for a chemical-mechanical polishing
process.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The invention provides a chemical-mechanical polishing (CMP)
system comprising a polishing component, a water-soluble silicate
compound in an amount sufficient to provide about 0.1 wt. % or more
of SiO.sub.2, an oxidizing agent that oxidizes at least part of a
substrate, and water, wherein the pH of the polishing system is
about 8 to about 12. The water and any components dissolved or
suspended therein form the polishing composition of the
chemical-mechanical polishing system. The amounts of the components
recited herein are based on the total weight of the polishing
composition unless otherwise noted (i.e., the weight of the water
and any components dissolved or suspended therein).
[0009] The polishing component is selected from the group
consisting of a polishing pad, an abrasive, and the combination of
a polishing pad and an abrasive. If an abrasive is present, the
abrasive can be in any suitable form (e.g., abrasive particles).
The abrasive can be fixed on the polishing pad and/or can be in
particulate form and suspended in the water. The polishing pad can
be any suitable polishing pad, many of which are known in the
art.
[0010] The abrasive can be any suitable abrasive, for example, the
abrasive can be natural or synthetic, and can comprise metal oxide,
carbide, nitride, carborundum, and the like. The abrasive also can
be a polymer particle or a coated particle. The abrasive desirably
comprises a metal oxide. Preferably, the metal oxide is selected
from the group consisting of alumina, ceria, silica, zirconia,
co-formed products thereof, and combinations thereof. The abrasive
particles typically 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 30 nm to
about 400 mn (e.g., about 40 nm to about 300
[0011] mn, or about 50 mn to about 250 nm, or about 75 nm to about
200 nm).
[0012] When the abrasive is suspended in the water (i.e., when the
abrasive is a component of the polishing composition), any suitable
amount of abrasive can be present in the polishing composition.
Typically, about 0.01 wt. % or more (e.g., about 0.05 wt. % or
more) abrasive will be present in the polishing composition. More
typically, about 0.1 wt. % or more abrasive will be present in the
polishing composition. The amount of abrasive in the polishing
composition typically will not exceed about 20 wt. %, more
typically will not exceed about 10 wt. % (e.g., will not exceed
about 5 wt. %). Preferably, the amount of abrasive in the polishing
composition is about 0.05 wt. % to about 2 wt. %, and more
preferably about 0.1 wt. % to about 1 wt. %.
[0013] The polishing system can comprise 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.
[0014] The polishing system comprises a water-soluble silicate
compound. The water-soluble silicate compound can be any suitable
water-soluble silicate compound. Desirably, the water-soluble
silicate compound is an alkali metal silicate. Preferably, the
water-soluble silicate compound is selected from the group
consisting of potassium silicate, sodium silicate, potassium
metasilicate, and sodium metasilicate. More preferably, the
water-soluble silicate compound is potassium silicate.
[0015] Water-soluble silicate compounds suitable for use in the
invention can be silicate glasses. Silicate glasses are typically
prepared by high-temperature fusion of silica sand with a suitable
alkali metal compound (e.g., sodium carbonate or potassium
carbonate).
[0016] Water-soluble silicates have the general formula
M.sub.2O.mSiO.sub.2.nH.sub.2O, where M is an alkali metal selected
from the group consisting of sodium, potassium and lithium, and m,
referred to as the modulus, and n are the number of moles of
SiO.sub.2 and H.sub.2O, respectively, per mole of M.sub.2O. The
modulus m is the molar ratio of SiO.sub.2 to M.sub.2O. The weight
ratio of SiO.sub.2 to M.sub.2O is also commonly used to describe
the composition of water-soluble alkali metal silicates. The
modulus m can be any suitable positive nonzero number (e.g., about
1 or more), typically about 1 to about 4, and more typically about
2 to about 4 (e.g., about 2.8 to about 3.9, or about 3 to about
3.6).
[0017] In a preferred embodiment, the water-soluble silicate
compound is potassium silicate having a general formula
K.sub.2O.mSiO.sub.2 wherein the modulus m (e.g., the molar ratio of
SiO.sub.2 to K.sub.2O) is a positive nonzero number. The potassium
silicate can have any suitable modulus. Desirably, the modulus is
about 1 or more. Preferably, the modulus is about 2.8 to about 3.9.
More preferably, the modulus is about 3 to about 3.6.
[0018] The water-soluble silicate compound is present in aqueous
solution in the polishing composition. A method of providing the
water-soluble silicate compound is to dissolve a solid form of the
water-soluble silicate compound in water to provide a solution.
Alternatively, a concentrated solution of the water-soluble
silicate compound can be diluted to obtain the desired
concentration of the water-soluble silicate compound in solution.
Various grades of potassium silicate and sodium silicate solutions
in water are available commercially, wherein the solutions are
characterized by the particular modulus of the silicates used in
their preparation, as well as wt. % SiO.sub.2 and wt. % K.sub.2O or
Na.sub.2O of the solutions. Zaclon, Inc. (Cleveland, Ohio) and PQ
Corporation (Valley Forge, Pa.) are two major suppliers of both
solid forms and solutions of potassium silicate and sodium
silicate.
[0019] Aqueous solutions of potassium silicate also can be obtained
by hydrothermal processes, wherein a silicon dioxide (e.g.,
SiO.sub.2) source is reacted with aqueous solutions of potassium
hydroxide under conditions of elevated temperature and/or pressure.
Examples of suitable hydrothermal processes for production of
aqueous solutions of potassium silicate are disclosed in U.S. Pat.
Nos. 5,084,262 and 5,238,668.
[0020] The polishing composition of the polishing system can
comprise any suitable amount of the water-soluble silicate
compound. Generally, the content of the water-soluble silicate
compound present in the polishing composition is expressed as the
weight percent of SiO.sub.2 provided by the water-soluble silicate
compound, based on the total weight of water and any components
dissolved therein. It will be understood that the formula
"SiO.sub.2" is a formal representation to allow for the calculation
of the amount of water-soluble silicate compound useful in the
polishing composition regardless of the source thereof (e.g.,
aqueous solutions or solid forms of water-soluble silicate
compounds of various compositions as described herein). Typically,
the polishing composition comprises sufficient water-soluble
silicate compound to provide about 0.1 wt. % or more (e.g., about
0.25 wt. % or more, about 0.5 wt. % or more, about 1 wt. % or more,
about 1.5 wt. % or more, or about 2 wt. % or more) of SiO.sub.2.
The polishing composition preferably comprises sufficient
water-soluble silicate compound to provide about 8 wt. % or less
(e.g., about 6 wt. % or less, or about 4 wt. % or less, or even
about 3 wt. % or less) of SiO.sub.2. The polishing composition most
preferably comprises about 0.25 wt. % to about 5 wt. % (e.g., about
0.5 wt. % to about 4 wt. %, or about 1 wt. % to about 3 wt. %) of
SiO.sub.2.
[0021] The polishing composition of the polishing system comprises
an oxidizing agent that oxidizes at least a part of a substrate.
Any suitable oxidizing agent can be used in conjunction with the
invention. Suitable oxidizing agents include inorganic and organic
per-compounds, bromates, nitrates, chlorates, chromates, iodates,
iron and copper salts (e.g., nitrates, sulfates, EDTA salts, and
citrates), rare earth and transition metal oxides (e.g., osmium
tetraoxide), potassium ferricyanide, potassium dichromate, iodic
acid, quinones, and the like. 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, and di-tert-butyl peroxide, monopersulfates
(SO.sub.5.sup.2-), dipersulfates (S.sub.2O.sub.8.sup.2-), and
sodium peroxide. Examples of compounds containing an element in its
highest oxidation state include but are not limited to periodic
acid, periodate salts, perbromic acid, perbromate salts, perchloric
acid, perchlorate salts, perboric acid, perborate salts, and
permanganates. Preferably, the oxidizing agent is selected from the
group consisting of hydrogen peroxide, iodates, permanganates,
persulfates, hydrogen peroxymonosulfate sulfates, molybdates,
ferric nitrate, nitrates, quinones, and combinations thereof. More
preferably, the oxidizing agent is potassium iodate or hydrogen
peroxide.
[0022] When the oxidizing agent is a salt, the oxidizing agent can
have any suitable cation. Non-limiting examples of suitable cations
include potassium, ammonium, and the like.
[0023] When the oxidizing agerit is a quinone, the oxidizing agent
can be any suitable quinone. Non-limiting examples of suitable
quinones include benzoquinones, naphthoquinones, and
anthraquinones. The quinone can be substituted at any available
position with any suitable substituent(s) or combinations of
substituents. Preferred substituents include groups that confer
solubility or emulsifiability of the quinone in the water of the
polishing composition. Suitable substituents include, without
limitation, hydroxyl, amino, monoalkylamino, dialkylamino, sulfonic
acid, carboxyl, phosphonic acid, salts thereof, and combinations
thereof. In an embodiment, the quinone is substituted with at least
one hydroxyl group. In other embodiments, the quinone is
substituted with at least one acidic substituent or a salt thereof.
Preferably, the at least one acidic substituent is selected from
the group consisting of sulfonic acid, carboxyl, and phosphonic
acid. More preferably, the at least one acidic substituent is
sulfonic acid (--SO.sub.3H). It will be appreciated that the acidic
substituents are capable of forming salts, and in this regard the
quinone having acidic substituents can exist as an acid, salt, or
when di- or polysubstituted can exist as a partial salt (e.g., a
monosalt of a disulfonic acid). Quinones having acidic substituents
can be supplied for use in the inventive polishing composition in
either acid form or salt form. Preferred anthraquinones are
selected from the group consisting of anthraquinone-2,6-disulfonic
acid, anthraquinone-2-sulfonic acid, anthraquinone-1,8-disulfonic
acid, anthraquinone-1,5-disulfonic acid, acid blue 45, salts
thereof, and combinations thereof. Preferred benzoquinones include
1 ,4-benzoquinone and 2,5-dihydroxy- 1 ,4-benzoquinone. Preferred
naphthoquinones include 1,2-naphthoquinone-4-sulfonic acid and
salts thereof.
[0024] The concentration of oxidizing agent in the polishing
composition of the polishing system desirably is about 1 mM or more
(e.g., about 2 mM or more, or about 3 mM or more, or about 5 mM or
more). The concentration of oxidizing agent in the polishing
composition preferably is about 1 M or less (e.g., about 0.5 M or
less, or about 0.25 M or less, or about 0.1 M or less). The desired
concentration of oxidizing agent can be achieved by any suitable
means, such as by using about 0.05 wt. % to about 20 wt. % of the
oxidizing agent based on the weight of the water and any components
dissolved or suspended therein in the preparation of the polishing
composition.
[0025] The polishing system has a pH of about 8 to about 12.
Preferably, the polishing system has a pH of about 8 to about 11,
more preferably about 9 to about 11. The pH of the polishing system
can be achieved and/or maintained by any suitable means. More
specifically, the polishing system can further comprise a pH
adjustor, a pH buffering agent, or a combination thereof. Aqueous
solutions of water-soluble silicate compounds obtained by
dissolution of silicate glasses (e.g., alkali metal silicates) or
prepared by hydrothermal processes have a strongly basic pH of
about 11 or more, being composed of a salt of a strong base and a
weak acid. The pH of the polishing system can be adjusted if
desired by acidifying a strongly basic solution of water-soluble
silicate compound by the addition of a sufficient amount of an acid
to neutralize sufficient M.sub.2O that is present to obtain the
desired pH. The pH adjustor can be any suitable pH-adjusting
compound. For example, the pH adjustor can be any suitable acid
strong enough to produce the desired final pH. Examples of suitable
acids include nitric acid, acetic acid, phosphoric acid, and the
like. The pH can be increased if desired by the addition of a
strong base. Examples of strong bases include potassium hydroxide,
ammonium hydroxide, and tetraalkylammonium hydroxide (e.g.,
tetramethylammonium hydroxide).
[0026] The pH buffering agent can be any suitable buffering agent,
for example, phosphates, acetates, borates, ammonium salts, and the
like. When a buffering agent is used to adjust the pH of the
polishing system, it will be understood that sufficient buffering
agent will be added to the polishing system to neutralize
sufficient M.sub.2O to provide the desired pH. The polishing system
can comprise any suitable amount of a pH adjustor and/or a pH
buffering agent, provided such amount is sufficient to achieve
and/or maintain the pH of the polishing system within the ranges
set forth herein.
[0027] The pH of the polishing system can be adjusted at any
suitable time. For example, the pH can be adjusted after addition
of the water-soluble silicate compound to the polishing composition
of the polishing system as described herein. A desired amount of a
water-soluble silicate compound also can be added to the polishing
composition, wherein the polishing composition comprises a
sufficient amount of a pH adjustor and/or a pH buffering agent such
that the desired pH is obtained after complete mixing of the
water-soluble silicate compound with the polishing composition. In
still other embodiments, the pH of the polishing system is adjusted
at the point-of-use (e.g., at the surface of the substrate).
[0028] The polishing system optionally comprises a corrosion
inhibitor (i.e., a film-forming agent). The corrosion inhibitor can
be any suitable corrosion inhibitor for any component(s) of the
substrate. Preferably, the corrosion inhibitor is a
copper-corrosion inhibitor. For the purposes of this invention, a
corrosion inhibitor is any compound, or mixture of compounds, that
facilitates the formation of a passivation layer (i.e., a
dissolution-inhibiting layer) on at least a portion of the surface
being polished. Useful corrosion inhibitors include, for example,
nitrogen-containing heterocyclic compounds. The corrosion inhibitor
desirably comprises one or more 5- or 6-membered, heterocyclic,
nitrogen-containing rings. Preferred corrosion inhibitors include
1,2,3-triazole, 1,2,4-triazole, benzotriazole, benzimidazole,
benzothiazole, and derivatives thereof, such as, for example,
hydroxy-, amino-, imino-, carboxy-, mercapto-, nitro-, urea-,
thiourea-, or alkyl-substituted derivatives thereof. Most
preferably, the corrosion inhibitor is selected from the group
consisting of benzotriazole, 1,2,3-triazole, 1,2,4-triazole, and
mixtures thereof. The polishing system of the invention can
comprise any suitable amount of the corrosion inhibitor. Generally,
the polishing composition of the polishing system comprises about
0.005 wt. % to about 1 wt. % (e.g., about 0.01 to about 0.5 wt. %,
or about 0.02 to about 0.2 wt. %) of the corrosion inhibitor.
[0029] The polishing system optionally further comprises one or
more other additives. Such additives include any suitable
surfactant and/or Theological control agent. Suitable surfactants
include, for example, cationic surfactants, anionic surfactants,
anionic polyelectrolytes, nonionic surfactants, amphoteric
surfactants, fluorinated surfactants, mixtures thereof, and the
like.
[0030] The polishing system optionally further comprises an
antifoaming agent. The anti-foaming agent can be any suitable
anti-foaming agent. Suitable antifoaming agents include, but are
not limited to, silicon-based and acetylenic diol-based antifoaming
agents. The amount of anti-foaming agent present in the polishing
composition of the polishing system typically is about 40 ppm to
about 140 ppm.
[0031] The polishing system optionally further comprises a biocide.
The biocide can be any suitable biocide, for example an
isothiazolinone biocide. The amount of biocide used in the
polishing system typically is about 1 ppm to about 500 ppm, and
preferably is about 10 ppm to about 200 ppm.
[0032] The polishing composition of the polishing system 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., abrasive, water-soluble silicate compound, etc.)
as well as any combination of ingredients (e.g., abrasive,
water-soluble silicate compound, oxidizing agent, etc.).
[0033] The polishing composition of the polishing system 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
water-soluble silicate compound, an oxidizing agent, and water in
amounts such that, upon dilution of the concentrate with an
appropriate amount of water, each component of the polishing
composition will be present in the polishing composition in an
amount within the appropriate range recited above for each
component. For example, the abrasive, a water-soluble silicate
compound, and oxidizing agent can each be present in the
concentrate in an amount that is about 2 times (e.g., about 3
times, about 4 times, or about 5 times) greater than the
concentration recited above for each component so that, when the
concentrate is diluted with an equal volume of water (e.g., 2 equal
volumes water, 3 equal volumes of water, or 4 equal volumes of
water, respectively), each component will be present in the
polishing composition in an amount within the ranges set forth
above for each component. Furthermore, as will be understood by
those of ordinary skill in the art, the concentrate can contain an
appropriate fraction of the water present in the final polishing
composition in order to ensure that the water-soluble silicate
compound, oxidizing agent, and other suitable additives are at
least partially or fully dissolved in the concentrate.
[0034] Any of the components used in conjunction with the invention
can be provided in the form of a mixture or solution in water. Two
or more components then desirably are individually stored and
subsequently mixed to form the polishing composition of the
polishing system. In this regard, it is suitable for the polishing
composition to be prepared (e.g., for all the components to be
mixed together) and then delivered to the surface of the substrate.
It is also suitable for the polishing composition to be prepared on
the surface of the substrate, through delivery of the components of
the polishing composition from two or more distinct sources,
whereby the components of the polishing composition meet at the
surface of the substrate (e.g., at the point-of-use). In either
case, the flow rate at which the components of the polishing
composition are delivered to the surface of the substrate (i.e.,
the delivered amount of the particular components of the polishing
composition) can be altered prior to the polishing process and/or
during the polishing process, such that the polishing
characteristics, such as the polishing rate, of the polishing
system is altered.
[0035] The polishing composition can be supplied as a one package
system comprising a water-soluble silicate compound, an oxidizing
agent, and water. Alternatively, the water-soluble silicate
compound and water can be supplied in a first container, and an
oxidizing agent can be supplied in a second container, either in
dry form, or as a solution or dispersion in water. Optional
components, such as an abrasive, a surfactant, and/or a corrosion
inhibitor, can be placed in the first and/or second containers or a
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
or solution. Moreover, it is suitable for the components in the
first or second containers to have different pH values, or
alternatively to have substantially similar, or even equal, pH
values. If an optional component such as an abrasive is a solid, it
may be supplied either in dry form or as a mixture in water. The
oxidizing agent desirably is supplied separately from the other
components of the polishing composition and is combined, e.g., by
the end-user, with the other components of the polishing
composition shortly before use (e.g., 1 week or less prior to use,
1 day or less prior to use, 1 hour or less prior to use, 10 minutes
or less prior to use, or 1 minute or less prior to use). 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.
[0036] While the components of the polishing composition of the
polishing system can be combined well before or even shortly before
use, the components of the polishing composition can be combined at
or near the point-of-use. As utilized herein, the term
"point-of-use" refers to the point at which the polishing
composition is contacted with the substrate surface). When the
components of the polishing composition are to be combined using
point-of-use mixing, the components of the polishing composition
are separately stored in two or more storage devices.
[0037] In order to mix components of the polishing composition
contained in storage devices at or near the point-of-use, the
storage devices typically are provided with one or more flow lines
leading from each storage device to the point-of-use of the
polishing composition (e.g., the platen or the substrate surface).
By the term "flow line" is meant a path of flow from an individual
storage container to the point-of-use of the component stored
therein. The one or more flow lines can each lead directly to the
point-of-use, or, in the case that more than one flow line is used,
two or more of the flow lines can be combined at any point into a
single flow line that leads to the point-of-use. Furthermore, any
of the one or more flow lines (e.g., the individual flow lines or a
combined flow line) can first lead to one or more of the other
devices (e.g., pumping device, measuring device, mixing device,
etc.) prior to reaching the point-of-use of the component(s).
[0038] The components of the polishing composition can be delivered
to the point-of-use independently (e.g., the components are
delivered to the substrate surface whereupon the components are
mixed during the polishing process), or the components can be
combined immediately before delivery to the point-of-use.
Components are combined "immediately before delivery to the
point-of-use" if they are combined less than 10 seconds prior to
reaching the point-of-use, preferably less than 5 seconds prior to
reaching the point-of-use, more preferably less than 1 second prior
to reaching the point of use, or even simultaneous to the delivery
of the components at the point-of-use (e.g., the components are
combined at a dispenser). Components also are combined "immediately
before delivery to the point-of-use" if they are combined within 5
m of the point-of-use, such as within 1 m of the point-of-use or
even within 10 cm of the point-of-use (e.g., within 1 cm of the
point of use).
[0039] When two or more of the components of the polishing
composition of the polishing system are combined prior to reaching
the point-of-use, the components can be combined in the flow line
and delivered to the point-of-use without the use of a mixing
device. Alternatively, one or more of the flow lines can lead into
a mixing device to facilitate the combination of two or more of the
components. Any suitable mixing device can be used. For example,
the mixing device can be a nozzle or jet (e.g., a high pressure
nozzle or jet) through which two or more of the components flow.
Alternatively, the mixing device can be a container-type mixing
device comprising one or more inlets by which two or more
components of the polishing composition are introduced to the
mixer, and at least one outlet through which the mixed components
exit the mixer to be delivered to the point-of-use, either directly
or via other elements of the apparatus (e.g., via one or more flow
lines). Furthermore, the mixing device can comprise more than one
chamber, each chamber having at least one inlet and at least one
outlet, wherein two or more components are combined in each
chamber. If a container-type mixing device is used, the mixing
device preferably comprises a mixing mechanism to further
facilitate the combination of the components. Mixing mechanisms are
generally known in the art and include stirrers, blenders,
agitators, paddled baffles, gas sparger systems, vibrators,
etc.
[0040] The invention further provides a method of polishing a
substrate using the polishing system described herein. The method
of polishing a substrate comprises (i) contacting a substrate with
the aforementioned polishing system, and (ii) abrading or removing
at least a portion of the substrate to polish the substrate.
[0041] In particular, the method of the invention comprises the
steps of (i) contacting a substrate with a chemical-mechanical
polishing system comprising a polishing component, a water-soluble
silicate compound in an amount sufficient to provide about 0.1 wt.
% or more of SiO.sub.2, an oxidizing agent that oxidizes at least
part of a substrate, and water, wherein the pH of the polishing
system is about 8 to about 12, and (ii) abrading at least a portion
of the substrate to polish the substrate.
[0042] In accordance with the invention, the substrate can be
polished with the polishing system described herein by any suitable
technique. The method of the invention is particularly well-suited
for use in conjunction with a chemical-mechanical polishing (CMP)
apparatus. Typically, the 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
that holds a substrate to be polished by contacting and moving
relative to the surface of the polishing pad. The polishing of the
substrate takes place by the substrate being placed in contact with
the polishing system of the invention, and by the polishing pad
moving relative to the substrate, with the other components of the
polishing system therebetween, so as to abrade and remove a portion
of the substrate so as to polish at least a portion of the
substrate.
[0043] The substrate can be any suitable substrate that is capable
of being polished by the inventive method. The substrate can
comprise metals (e.g., copper, tantalum, aluminum, titanium,
molybdenum, and the like), metal alloys (e.g., stainless steel,
cobalt-chrome, and the like), semiconductors (e.g., gallium
nitride, gallium arsenide, and the like), ceramics (e.g., silicon
carbide), polymers (e.g., polycarbonate), optical materials (e.g.,
sapphire, zinc sulfide, zinc selenide, and the like), diamond, and
insulating materials.
[0044] The substrate can comprise any suitable microelectronic
substrate (e.g., an integrated circuit, metals, ILD layers,
semiconductors, thin films, MEMS, magnetic heads) and can further
comprise any suitable insulating, metal, or metal alloy layer
(e.g., metal conductive layer). Preferably, the metal layer
comprises tantalum. More preferably, the substrate further
comprises a metal layer comprising copper. The insulating layer can
be a metal oxide, porous metal oxide, glass, organic polymer,
fluorinated organic polymer, or any other suitable high or low-k
insulating layer. The insulating layer preferably comprises a
dielectric material which has a dielectric constant of about 3.5 or
lower.
[0045] Examples of low dielectric constant (i.e., low-k dielectric)
materials include but are not limited to fluorine doped silicon
dioxide, an organically modified silicon glass such as carbon doped
silicon dioxide (CDO), fluorinated carbon, and organic materials
such as fluorinated and unfluorinated parylene and polyimide. The
low-k dielectrics can be porous or nonporous. Examples of porous
low dielectric materials are porous hydrosilsesquioxane or porous
methyl silsesquioxane, porous silica structures such as aerogel,
low temperature deposited silicon carbon films, low temperature
deposited Si--O--C films, and methyl doped porous silica.
Preferably, the insulating layer is an organically modified silicon
glass or a carbon-doped silicon dioxide.
[0046] Advantageously, the polishing system of the invention allows
for reduction of the coefficient of friction associated with
chemical-mechanical polishing of a substrate, while maintaining
acceptable polishing rates.
[0047] 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 substrate are known in the art. Desirably, the inspection or
monitoring of the progress of the polishing process with respect to
a substrate 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 substrate.
[0048] The following example further illustrates the invention but,
of course, should not be construed as in any way limiting its
scope
EXAMPLE
[0049] This example demonstrates the reduction in the coefficient
of friction observed in the polishing of a substrate comprising
tantalum using the inventive method.
[0050] Similar substrates comprising a 250 nm layer of tantalum
were polished with different polishing compositions (Polishing
Compositions A and B). Each of Polishing Compositions A and B
contained 0.5 wt. % of ceria and 0.20 wt. % of potassium iodate in
water at a pH of 11. Polishing Composition B further contained 3
wt. % of potassium silicate.
[0051] The substrates were polished for 60 seconds using a
polyurethane polishing pad on a Logitech Model CDP polisher using
the following polishing parameters: 13.8 kPa (2 psi) downforce
pressure of the substrate against the polishing pad, 66 rpm platen
speed, 70 rpm carrier speed, 160 mL/min polishing composition flow
rate, and use of a polyurethane polishing pad. Following polishing,
the removal rate was determined using resistivity measurements.
[0052] The coefficient of friction was determined by the
relationship of the displacement of the carrier shaft during the
polishing operation to the force generated by friction between the
polishing pad and the substrates. Referring to the Figure, a
non-contact capacitive displacement sensor (10) electrically
connected to a recording device (20) was positioned adjacent to the
carrier shaft (30) of the polisher (40) with a gap (50)
therebetween. Displacement of the carrier shaft caused by force F
(60) resulting from frictional force generated during the polishing
of the substrates resulted in a change in the output voltage of the
sensor. A calibration curve was obtained by measurement of sensor
output voltage as a function of known force applied to the carrier
shaft in a direction normal to the central axis of the carrier
shaft. The average force F.sub.a applied to the carrier shaft
during the polishing experiments was determined from the
calibration curve using the average output voltage over the 60
second polishing time. The coefficient of friction .mu. was
calculated from force F.sub.a and downforce pressure (70) of the
substrate (80) against the polishing pad P (90) from the equation:
.mu.=F.sub.a/P. The results are set forth in the Table.
TABLE-US-00001 TABLE Effect of Potassium Silicate on Coefficient of
Friction and Tantalum Removal Rate Polishing Removal Rate
Coefficient of Composition (.ANG./min) Friction (.mu.) A
(comparative) 339 0.45 B (invention) 300 0.35
[0053] As is apparent from the results set forth in the Table, the
presence of 3 wt. % of potassium silicate in the inventive
polishing composition resulted in an approximately 20% reduction in
the coefficient of friction observed in the polishing of a
substrate comprising a layer of tantalum, while the tantalum
removal rate was decreased by only approximately 12%. Thus, the
results of this example demonstrate the friction reduction
achievable by the polishing composition and method of the
invention.
[0054] 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.
[0055] 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.
[0056] 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.
* * * * *