U.S. patent application number 10/851684 was filed with the patent office on 2005-01-06 for synthesis of chemically reactive ceria composite nanoparticles and cmp applications thereof.
This patent application is currently assigned to Ferro Corporation. Invention is credited to Feng, Xiangdong, Her, Yie-Shein, Mao, Yun.
Application Number | 20050003744 10/851684 |
Document ID | / |
Family ID | 26944462 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050003744 |
Kind Code |
A1 |
Feng, Xiangdong ; et
al. |
January 6, 2005 |
Synthesis of chemically reactive ceria composite nanoparticles and
CMP applications thereof
Abstract
The present invention provides a method of synthesizing
nanosized abrasive particles and methods of using the same in
chemical mechanical polishing slurry applications. The nanosized
abrasive particles according to the invention are produced by
hydrothermal synthesis. The crystallites of the particles include
cerium atoms and atoms of metals other than cerium. In a preferred
embodiment of the invention, the crystallites exhibit a cubic
crystal lattice structure. The differences in electric potential
between the cerium atoms and the atoms of metals other than cerium
facilitate the polishing of films without the need for chemical
oxidizers.
Inventors: |
Feng, Xiangdong; (Broadview
Heights, OH) ; Her, Yie-Shein; (Canandaigua, NY)
; Mao, Yun; (Geneva, NY) |
Correspondence
Address: |
RANKIN, HILL, PORTER & CLARK, LLP
925 EUCLID AVENUE, SUITE 700
CLEVELAND
OH
44115-1405
US
|
Assignee: |
Ferro Corporation
1000 Lakeside Avenue
Cleveland
OH
44114
|
Family ID: |
26944462 |
Appl. No.: |
10/851684 |
Filed: |
May 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10851684 |
May 21, 2004 |
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10255136 |
Sep 25, 2002 |
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6818030 |
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10255136 |
Sep 25, 2002 |
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09992485 |
Nov 16, 2001 |
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6596042 |
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Current U.S.
Class: |
451/41 ; 423/263;
51/307; 51/309 |
Current CPC
Class: |
C01P 2004/51 20130101;
C03C 19/00 20130101; C01F 17/235 20200101; C01P 2002/60 20130101;
C09C 1/3653 20130101; C01P 2004/64 20130101; C09K 3/1409 20130101;
C01P 2004/62 20130101; B82Y 30/00 20130101; C01P 2006/90 20130101;
C01G 23/053 20130101; C01P 2002/76 20130101; C01G 23/04 20130101;
C01F 17/224 20200101 |
Class at
Publication: |
451/041 ;
051/307; 051/309; 423/263 |
International
Class: |
B24D 003/02; B24B
001/00 |
Claims
What is claimed:
1. A method of producing abrasive particles for use in CMP slurries
comprising: a. providing an aqueous reaction mixture comprising i.
one or more compounds that provide a source of cerium ions, ii. one
or more compounds that provide a source of metal ions selected from
the group consisting of Be, B, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag,
Cd, In, Sn, Sb, Te, Ba, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Hp, Er,
Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, and
combinations thereof, b. contacting the aqueous reaction mixture
with a base to raise the pH to above about 1.5, and, c. subjecting
the aqueous reaction mixture to hydrothermal treatment at a
temperature of from about 70.degree. C. to about 500.degree. C. to
produce the abrasive particles, d. wherein the abrasive particles
comprise crystallites having crystal lattice structures that
include cerium and one or more metals other than cerium.
2. The method of claim 1 wherein the ratio of cerium ions to guest
ions is about 100000:1 to about 1:100000.
3. The method of claim 1 where the compound that provides the
source of cerium ions is a Ce(III) salt or a Ce(IV) salt.
4. The method of claim 1 wherein the reaction mixture is subjected
to hydrothermal treatment for about 10 minutes to about 48
hours.
5. The method of claim 4 wherein the aqueous reaction mixture is
contacted with the base by double jet injection.
6. The method of claim 5 wherein the compound that provides the
source of guest ions is a salt of the guest ion.
7. The method of claim 6 wherein the compound that provides the
source of guest ions is selected from the group consisting of
Fe(NO.sub.3).sub.3, Cu(NO.sub.3).sub.2, Nd(NO.sub.3).sub.3, and
hydrated forms thereof.
8. The method of claim 1 wherein the particles have a crystallite
size of about 5 to about 100 nm.
9. The method of claim 1 wherein the particles agglomerate to form
a secondary particle size of about 50 to about 500 nm.
10. A method of making composite CMP ceria particles comprising: a.
contacting an aqueous solution of
Ce(NH.sub.4).sub.2(NO.sub.3).sub.6 with a second metal salt to form
a reaction mixture; b. contacting the reaction mixture with a base
to raise the pH to above about 1.5; and c. heating the reaction
mixture to form the particles.
11. The method of claim 10 wherein the second reaction mixture is
heated for about 10 minutes to about 48 hours at a temperature of
about 70.degree. C. to about 500.degree. C.
12. The method of claim 10 wherein the first reaction mixture is
contacted with the base by double jet injection
13. The method of claim 10 wherein the second metal salt is
selected from the group consisting of nitrates, chlorides,
bromides, sulfates, perchlorides, and acetates of iron, copper and
neodymium in their anhydrous and hydrated forms.
14. The method of claim 10 wherein the second metal salt is
selected from the group consisting of Fe(NO.sub.3).sub.3,
Cu(NO.sub.3).sub.2, Nd(NO.sub.3).sub.3, and hydrated forms
thereof.
15. A method of removing a film at a desired rate in the absence of
chemical oxidizers comprising: a. determining the desired polishing
rate of film to be removed; b. selecting abrasive particles
according to claim 1 that provide a desired polishing rate for the
film be removed; and c. polishing the film with a CMP slurry
comprising the particles selected in step b.
16. The method of claim 15 wherein the film be removed is selected
from the group consisting of silver, gold, platinum, copper,
palladium, nickel, cobalt, iron, ruthenium, iridium, and osmium,
silicon, aluminum, germanium, tungsten, tantalum, and alloys or
blends thereof.
17. The method of claim 15 wherein the film to be removed is
selected from the group consisting of oxides, nitrides or silicides
of boron, sodium, magnesium, aluminum, silicon, phosphorus,
potassium, calcium, gallium, germanium, arsenic, selenium,
rubidium, strontium, yttrium, zirconium, tin, antimony, cesium,
nickel, cobalt and barium.
18. The method of claim 15 wherein the film to be removed is a
polymer is selected from the group consisting of
poly(para-xylylenes), halogenated poly(para-xylylenes), b-staged
polymers, polyimides, halogenated polyimides, silsequioxanes, alkyl
substituted silsequioxanes, poly-(arylene ethers) and
poly-(tetrafluoroethylene).
19. The method of claim 15 wherein the CMP slurry further comprises
a pH adjuster.
20. A CMP slurry comprising: a. water; and b. abrasive particles
according to claim 1.
21. The CMP slurry of claim 20 wherein the slurry is substantially
free of chemical additives/oxidizers.
22. The CMP slurry of claim 20 wherein the ratio of cerium ions to
guest ions is about 1000:1 to about 1:1000.
23. The CMP slurry of claim 21 wherein the guest ion is selected
from the group consisting of Fe, Nd, and Cu.
24. The CMP slurry of claim 21 wherein the guest ion is selected
from the group consisting of Ti, Ta and Y.
25. A method of removing a portion of a substrate in a CMP
operation comprising: a. providing the CMP slurry of claim 20; b.
adjusting the pH of the slurry to 3.0 to 11.0 using at least one pH
adjuster; c. contacting the slurry and the substrate to be
polished; and d. performing CMP on the substrate using said
slurry.
26. The method of claim 25 wherein the difference in
electronegativity of the cerium ions and the guest ions is
sufficient to drive a redox reaction between the particle and the
substrate when the particle contacts the substrate.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending
Appn. Ser. No. 10/255,136, filed Sep. 25, 2002, which is a
continuation in part of Appn. Ser. No. 09/992,485, filed Nov. 16,
2001, now U.S. Pat. No. 6,596,042.
FIELD OF THE INVENTION
[0002] The present invention provides a process for producing
abrasive particles, the abrasive particles produced according to
the process, and a process for removing a film layer using a CMP
slurry containing particles made by the process.
BACKGROUND OF THE INVENTION
[0003] Chemical-mechanical polishing (CMP) slurries are used, for
example, to planarize surfaces during the fabrication of
semiconductor chips and related electronic components. CMP slurries
typically include reactive chemical agents and abrasive particles
dispersed in a liquid carrier. The abrasive particles perform a
grinding function when pressed against the surface being polished
using a polishing pad, and separately, the reactive chemical agents
serve to oxidize the surface.
[0004] It is well known that the size, composition, and morphology
of the abrasive particles used in a CMP slurry can have a profound
effect on the polishing rate and surface finishing. Over the years,
CMP slurries have been formulated using abrasive particles formed
using, for example, alumina (Al.sub.2O.sub.3), cerium oxide, or
ceria (CeO.sub.2), iron oxide (Fe.sub.2O.sub.3), silica
(SiO.sub.2), silicon carbide (SiC), silicon nitride
(Si.sub.3N.sub.4), tin oxide (SnO.sub.2), titania (TiO.sub.2),
titanium carbide (TiC), tungsten oxide (WO.sub.3), yttria
(Y.sub.2O.sub.3), zirconia (ZrO.sub.2), and combinations
thereof.
[0005] Known abrasive particles for use in CMP slurries include
colloidal silica, which is produced by condensation in aqueous
solution. Another is fumed silica, which may be produced by a
continuous flame hydrolysis technique involving the conversion of
silicon tetrachloride (SiCl.sub.4) to the gas phase using an
oxy-hydrogen flame. The silicon tetrachloride reacts with the
combustion by-produce (water) to yield silica (SiO.sub.2) and
hydrochloric acid: SiCl.sub.4+2H.sub.2O.fwdarw.SiO.sub.2+4HCl. The
HCl is easily separated as it remains in the gas phase, while the
fumed silica is solid. In order to attain a desired particle size,
the fumed silica is mechanically ground or milled. Fumed silica is
by far the most widely used abrasive particle.
[0006] Calcination is another method of producing abrasive
particles for use in CMP slurries. During the calcination process,
precursors such as carbonates, oxalates, nitrates, and sulfates,
are converted into their corresponding oxides at very high
temperature. After the calcination process is complete, the
resulting oxides must be milled to obtain particle sizes and
distributions that are proper to provide desired removal rate and
prevent scratching.
[0007] The calcination process, although widely used, does present
certain disadvantages. For example, it tends to be energy intensive
and can produce toxic and/or corrosive gaseous byproducts. In
addition, contaminants are easily introduced during the calcination
and subsequent milling processes. Finally, it is difficult to
obtain a narrow particle size distribution.
[0008] The basic mechanism of the CMP process is the simultaneous
formation of a removable surface layer, such as via oxidation of a
metal surface or via hydrolysis of an oxide or nitride layer,
coupled with the mechanical removal of the removable surface layer
using abrasive particles pressed between the work piece and a
polishing polishing pad that are in motion relative to each other.
In CMP slurries for removing copper films, the mechanical
(abrasive) effect and oxidizing function are separately provided by
the different components. That is, abrasive particles mainly
contribute the mechanical effect, while chemical oxidizing agents
give rise to a chemical (redox) reaction.
[0009] Numerous chemical additives exist to improve film removal
rates, to adjust the selectivity of removal rates between various
materials, and to allow better surface finishing and less defects.
Hydrogen peroxide, ferric nitrate, potassium iodate and periodate
are widely used as oxidizing chemicals in copper CMP slurries to
improve removal rates relative to slurries having only abrasive
particles. Most CMP slurries are formed by combining two separate
components, namely: (1) abrasive particles dispersed in a liquid
medium; and (2) chemical additives (e.g., a chemical oxidizer). The
separate components are mixed together immediately prior to use
and, once blended, have a shelf life of typically only about 5 days
or less. The chemical oxidizer in conventional CMP slurries tends
to lose its oxidative efficacy if it remains unused for long
periods.
[0010] While the use of chemical oxidizers improves the metal
removal rate to industrially practicable levels, the chemical
oxidizers in the slurry continue to oxidize metal until they are
expended or removed. Hence, chemical oxidizers are one of main
contributors to the problem of dishing or pitting of metal
surfaces, which results from continued oxidative attack on an
already planar metal surface, even in the absence of abrasive
particles.
BRIEF SUMMARY OF THE INVENTION
[0011] Broadly, the abrasive particles according to the invention
comprise crystallites (primary particles) that include cations of
cerium and cations of at least one other metal, which have been
formed by hydrothermal synthesis. The abrasive particles can be
used to formulate CMP slurries that provide industrially acceptable
removal rates of a variety of surface films (substrates), without
the need for added chemical oxidizers, which eliminates concerns
about dishing and cupping. Slurries formulated using abrasive
particles according to the invention exhibit a shelf life far
greater than traditional CMP slurries. Another advantage provided
by the abrasive particles according to the invention is that use of
chemical oxidizers can be avoided, which reduces the environmental
impact of producing electronic components.
[0012] The foregoing and other features of the invention are
hereinafter more fully described and particularly pointed out in
the claims, the following description setting forth in detail
certain illustrative embodiments of the invention, these being
indicative, however, of but a few of the various ways in which the
principles of the present invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a Table displaying several properties and
polishing rates of the abrasive particles formulated in Example
5.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The invention provides a method of synthesizing abrasive
particles having a desired reactivity, which can be used in
formulating CMP slurries exhibiting a variety of substrate removal
rates. The inventive particles may be used to polish metal
substrates or metal oxide substrates. Both operations are routinely
required in the manufacture of electronic components. The substrate
removal rate of CMP slurries is believed to depend on numerous
factors. A non-exhaustive list of such factors includes: the
composition of the abrasive particles; the relative level and
identity of guest metal ions in those particles; the size of the
primary particles (i.e., crystallite size); the size of secondary
particles (i.e., coalesced or agglomerated primary particles); the
concentration of abrasive particles in the slurry; the pH of the
slurry; and the presence and concentration of chemical oxidizers in
the slurry. The focus of the present invention is the control of
primary and secondary particle size of the abrasive particles, and
the control of the level of guest ions in such primary particles.
Chemically reactive abrasive particles according to the invention
can be used in the CMP process to produce both chemical and
mechanical effects.
[0015] It has been discovered that nanoscale composite ceria
particles can be synthesized hydrothermally such that cerium oxide
acts as a host matrix (crystal lattice structure) for guest metal
atoms (or ions) that take the place of cerium atoms (or ions) in
the crystal lattice structure of the host matrix. The inventive
process produces "nanoscale" particles, with primary particles
(crystallites) having a mean diameter (D.sub.50) in the range of
about 1 nm to about 10000 nm. In a preferred embodiment, the
average crystallite size may be about 5 to about 1000 nm, more
preferably about 10 to about 400 nm, still more preferably about 15
to about 200 nm, and even more preferably about 20 to about 100 nm.
Secondary particles, which are agglomerations of primary particles,
exhibit sizes within the range of from about 10 to about 10000 nm,
but are preferably 30 nm to about 1000 nm, more preferably from
about 40 to about 800 nm and still more preferably from about 50 to
about 500 nm. Throughout the instant specification and in the
appended claims, the term "particle" when used without further
explanation refers to secondary particles.
[0016] Generally, guest metal ions are substituted for a cerium
ions in the crystal lattice structure, thus preserving the ratio of
metal cations to oxygen ions in such crystal. Thus, for cerium
oxide, the mole ratio of metal atoms (or cations) to oxygen atoms
in the crystal lattice structure will be about 1:2, although mole
ratios of metal atoms to oxygen atoms of about 1:1.5 to 1:3.5 are
possible. The ratio of cerium atoms to oxygen atoms in the crystal
is sufficient to preserve overall statistical electroneutrality.
The resultant composite metal oxide formula is thus
Ce.sub.xM.sub.yO.sub.z where x+y is about 1 and z is within the
range of from about 1.5 to about 3.5. Because the guest metal ions
(1) may have a different oxidation state than cerium and/or (2) do
have a different electronegativity than cerium, the difference in
electrical potential is generally sufficient to drive a redox
reaction on the surface of a film to be polished when the abrasive
particles according to the invention are in contact therewith.
Films or substrates that can be polished (removed) using abrasive
particles according to the invention include metals, metal oxides,
metal nitrides, silicides, and polymers.
[0017] In particular, the invention provides a method of producing
abrasive particles for use in CMP slurries comprising providing an
aqueous reaction mixture comprising a source of cerium ions and a
source of metal ions other than cerium. The metal ions other than
cerium are selected from the group consisting of Be, B, Mg, Al, Si,
Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, As, Sr, Y, Zr, Nb,
Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Pr, Nd, Pm, Sm,
Eu, Gd, Tb, Dy, Hp, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au,
Hg, Tl, Pb, Bi and combinations thereof. The aqueous reaction
mixture is subjected to hydrothermal treatment at a temperature of
from about 70.degree. C. to about 500.degree. C. to produce the
abrasive particles. When the mole percentage of cerium atoms in the
crystal lattice structure of the crystallites exceeds the mole
percentage of guest metal ions, the crystallites will generally
exhibit a cubic crystal lattice structure wherein cerium serves as
a host cation and the metal other than cerium serves as a guest
cation. When the mole percentage of cerium atoms in the crystal
lattice structure is less than the mole percentage of guest metal
ions, the crystallites will generally exhibit a crystal lattice
structure determined by the guest metal ions, with the cerium
cation serving as guests therein. The inventive abrasive particles
can be dispersed in water to form CMP slurries. If desired, a pH
adjuster may be added to adjust the pH to about 3 to about 11.
[0018] The precise stoichiometry used in hydrothermal synthesis
dictates the final aggregate ratio of guest to host ions in the
crystal structures of a sample of the inventive composite
particles. An analysis of an aqueous dispersion of composite
abrasive particle formed in accordance with the invention that
included cerium as a host cation and titanium as a guest ion showed
that the dispersion consisted mainly of small particles having a
particle size distribution in the range of 6 to 30 nm, along with a
few larger particles having a size of about 160 nm. The smaller
particles exhibited a spherical shape, whereas the larger particles
appeared to be more rectangular. The EDS spectrum for the large
particles showed that they consist of 95 wt % ceria and 5 wt %
titania, while the smaller particles consist of 58 wt % ceria and
42 wt % titania. Thus, it will be appreciated that variations in
the relative mole percentage of cerium ions to guest ions will
occur in individual particles, which may be different than the
average relative mole percentage for the bulk of the particles. In
other words, while the aggregate composition of a dispersion of
inventive particles will have a makeup approximately the same as
the relative amounts of reagents used, the composition of a single
given particle, or any subset of particles from such a dispersion
may have a composition widely different from the aggregate.
[0019] In the aggregate, the mole ratio of cerium ions to guest
ions in abrasive particles according to the invention will be from
about 100000:1 to about 1:100000. In order to retain the desired
cubic crystal lattice structure of cerium oxide, the mole ratio of
cerium ions to guest ions in the abrasive particles according to
the invention will be within the range of from about 1000:1 to
about 1:1. Still more preferably, the aggregate mole ratio will be
within the range of from about 90:1 to about 1.5:1. It will be
appreciated that as the concentration of guest ions increases,
additional crystalline phases tend to appear in the primary
particles. For example, crystallites containing substantial molar
quantities of ceria and titania will exhibit both a cubic
crystalline phase and an anatase crystalline phase, although both
crystals contain ions of both cerium and titanium.
[0020] The cerium host ions may be provided by a Ce(III) salt or a
Ce(IV) salt, for example Ce(NH.sub.4).sub.2(NO.sub.3).sub.6. The
hydrothermal treatment may be carried out for about 10 minutes to
about 48 hours, preferably about 15 minutes to about 24 hours and
more preferably about 1 hour to 8 hours. It is believed that the
method of mixing the aqueous reaction mixture and a base has an
effect on primary and secondary particle sizes. For example,
blending a base into the aqueous reaction mixture by double jet
injection is effective in synthesizing composite ceria particles
having desired small crystallite sizes. Ceria particles having
crystallite sizes of about 10 nm to about 100 nm provide superior
polishing rates in CMP operations.
[0021] The reaction mixture may be heated to a temperature of about
70.degree. C. to about 500.degree. C., or to a temperature of about
200.degree. C. to about 400.degree. C. Preferably the second
reaction mixture is heated to a temperature of about 300.degree.
C.
[0022] The source of guest ions is not critical. Accordingly, the
source of guest metal ions may be a salt of the guest ion. The
guest ion salt may be selected from the group consisting of
nitrates, chlorides, perchlorides, bromides, sulfates, phosphates,
carbonates, and acetates of the guest ion. Metal ethoxides may also
be used. In a preferred embodiment, the source of guest ions may be
Fe(NO.sub.3).sub.3, Cu(NO.sub.3).sub.2, Nd(NO.sub.3).sub.3, or the
hydrated forms thereof.
[0023] These composite particles can be used as chemically reactive
abrasives in CMP slurries to remove metal film layers such as
copper without the need for added oxidizers. Metal oxides,
nitrides, silicides and polymers may also be polished effectively.
Metals that can be polished by the inventive methods include
silver, gold, platinum, copper, palladium, nickel, cobalt, iron,
ruthenium, iridium, and osmium, silicon, aluminum, germanium,
tungsten, tantalum and alloys or blends thereof.
[0024] Metal oxides that can be polished by the inventive methods
include oxides of metals such as boron, sodium, magnesium,
aluminum, silicon, phosphorus, potassium, calcium, gallium,
germanium, arsenic, selenium, rubidium, strontium, yttrium,
zirconium, tin, antimony, cesium, and barium. Metal oxide
substrates may also contain more than one of the aforementioned
oxides. Metal nitrides can also be polished.
[0025] Low K-value dielectric materials may also be polished. Many
of these are polymeric, for example poly-para-xylenes commercially
available from S. C. Cookson, of Indianapolis, Ind., under the
Parylene tradename. Further such polymers include fluorinated
polyimides, methyl silsesqioxane, and poly-(arylene ether)s. The
Dow Chemical Company, of Midland, Mich., commercially supplies
B-staged polymers including those sold by under the Cyclotene.RTM.
and SiLK.RTM. trademarks. For example, Cyclotene.RTM. 4026-46 is a
blend of B-staged divinylsiloxane-bis-benzocy- clobutene,
mesitylene, polymerized 1,2-dihydro-2,2,4-trimethylquinoline,
2,6-bis{(4-azidophenyl) methylene}-4-ethylcyclohexanone, and
1-1'-(1-methylethylidene) bis {4-(4-azidophenoxy)benzene}. In
general, the Cyclotene.RTM. dielectric polymers contain at least
B-staged divinylsiloxane-bis-benzocyclobutene and mesitylene.
Polymers sold under the SiLK.RTM. trademark are semiconductor
dielectric resins comprise a Dow proprietary b-staged polymer,
cyclohexanone, and gamma-butyrolactone. In addition, carbon doped
silica substrates, which are also known as SiCOH substrates, can be
polished.
[0026] The difference in valence state and/or electronegativity
between ceria and the guest ions in the abrasive particles
according to the invention gives the particles the ability to
provide the redox potential to films to be removed. Hence, it is
believed that such oxidation occurs only when a particle contacts
the substrate surface, and consequently, that oxidation and
mechanical abrasion occur simultaneously. This fact, combined with
the small particle size disclosed herein (nanoscale) provides
extremely precise polishing, and planarization that is both locally
and globally accurate. Thus, the invention further provides a
method of removing a film by CMP at a desired rate in the absence
of chemical oxidizers.
[0027] When all other polishing conditions are kept similar,
adjustments in the relative molar percentage of guest metal ions in
the crystal lattice structure of the abrasive particles according
to the invention can be used to determine or tune the rate of film
removal. Thus, the invention facilitates determining the rate of
removal of a film layer by selecting the composition of the
abrasive, rather than adjusting other polishing parameters.
[0028] The invention further provides a method of removing a
portion of a substrate by contacting the substrate with a CMP
slurry comprising composite abrasive particles wherein the abrasive
particles comprise cerium ions and guest metal ions selected from
the group consisting of iron, copper, neodymium, and combinations
thereof, and wherein the slurry contains no additional
oxidizers.
[0029] The invention also provides a method of producing a CMP
slurry comprising contacting the particles discussed hereinabove
with water to form a suspension and adjusting the pH of the
suspension to about 2.0 to about 11.0 with a pH adjuster, wherein
the slurry is substantially free of chemical additives and
oxidizers.
[0030] Because the particles of the present invention are so small,
i.e., primary particle diameters on the order of nanometers, a very
high fraction of the atoms reside at the particle crystalline
surfaces and grain boundaries. As primary particle size decreases,
the BET specific surface area (m.sup.2/gram) increases. Without
being limited to any theory, applicants postulate that
nanoparticles are much more reactive than the corresponding bulk
material due to vastly increased specific surface area. It is
further believed that surface defects, non-balanced charges, guest
ions in the grain boundary and vacancies in the crystalline lattice
and other surface active sites may beneficially induce or catalyze
chemical redox reactions.
[0031] Hydrothermal synthesis of cerium oxide abrasive particles is
disclosed in commonly owned U.S. Pat. No. 6,596,042, which is
hereby incorporated by reference. In order for the particles to
function as chemically active nanoparticles, the nanoparticles must
be able to form a stable suspension in water. In developing the
embodiments of the present invention, hydrothermal synthesis of
ceria was carried out in order to facilitate crystallization of the
desired abrasive oxide particles containing guest cations.
[0032] With respect to the present invention, hydrothermal
synthesis is conducted in a sealed (i.e., air-tight) container,
typically made of stainless steel. A metal salt containing the host
cation ingredient, i.e., cerium ions, is solubilized in deionized
water. A crystallization promoter is added, and optionally, a
stabilizer for the crystallization promoter is also added. The pH
of the inherently acidic salt solution is raised to at least 1.5,
preferably to at least 7.5, and more preferably to at least 9.0
using a base, (which may be provided in the form of a solution),
which assists in the formation of a solution having a gel-like
consistency. Suitable bases include, for example, NaOH, KOH,
NH.sub.4OH, organoamines such as urea, ethylamine and ethanolamine,
and/or polyorganoamines such as polyethylenimine. Combinations of
bases can also be used. Other compounds such as urea can also be
added to assist in crystal growth. The gel-like solution will break
down into small particles upon rapid stirring. Double injection
mixing can be used to ensure stoichiometric homogenization of the
metal salt solutions with the base(s) to ensure uniform crystal
seed generation. Hydrothermal synthesis is carried out in a closed
container because the pressure generated by the raised temperature
results in small particles having a narrow size distribution
resulting from uniform crystal growth. The solution may be further
diluted with deionized water as needed. The solution is transferred
to a sealed stainless steel reaction vessel, which is heated to
70-500.degree. C. for about 1 hour to about 500 hours under
stirring. The vessel is then cooled to room temperature, and the
slurry is washed until a low conductivity is achieved, typically
<5 mS, preferably <1 mS, more preferably <0.5 mS and most
preferably <0.1 mS. As a final purifying step, the particles may
be filtered using micron range filter paper.
[0033] Crystallization promoters include titanium chloride,
titanium sulfate, titanium bromide, organotitanium compounds such
as titanium oxychloride and those sold by E.I. DuPont de Nemours of
Wilmington, Del., under the Tyzor.RTM. trademark, for example
Tyzor.RTM.-TE. A preferred crystallization promoter is
Ti[OCH(CH.sub.3).sub.2)].sub.4 (titanium (IV) isopropoxide). It
will be appreciated that certain titanium compounds tend to rapidly
decompose in aqueous media, which reduces their efficiency in
promoting the formation of particles having larger crystallite
sizes. Accordingly, it is preferable for one or more stabilizing
compounds such as, for example, acetyl acetone, (i.e., acetyl
acetone titanate) to be present with the crystallization promoters
in order to prevent or delay their decomposition. Further details
on crystallization promoters and stabilizers can be found in
commonly owned U.S. Pat. No. 6,596,042, and copending application
Ser. No. 09/992,485. The guest ions are incorporated into the
cerium oxide crystal structure without disrupting the cubic
structure thereof.
[0034] Although the preceding description and following
experimental examples will show that the inventive abrasive
particles alone--absent oxidizers and other chemical additives--can
be used to exhibit a wide variety of satisfactory metal removal
rates on a copper substrate, the metal removal rates of any
inventive particle can be further adjusted by the use of chemical
additives, including oxidizers. Such chemical additives include
hydrogen peroxide, ascorbic acid, citric acid, formic acid, acetic
acid, propionic acid, butyric acid, valeric acid, acrylic acid,
lactic acid, succinic acid, nicotinic acid, oxalic acid, malonic
acid, tartaric acid, malic acid, glutaric acid, citric acid, maleic
acid, and glycine.
[0035] The following examples are intended only to illustrate the
invention and should not be construed as imposing limitations upon
the claims. The following experimental methods, conditions and
instruments were employed in preparing the exemplary CMP particles
detailed hereinbelow.
EXAMPLE 1
[0036] An abrasive particle suitable for CMP was prepared by first
dissolving 1854 g (3.38 mol) of Ce(NH.sub.4).sub.2(NO.sub.3).sub.6
in 3500 g of deionized water. To this solution, 100 g of
Ti(isopropoxide)4 (0.35 mol) and 90 g of acetyl acetone was added.
The cerium salt solution was mixed with a basic solution
(containing 1000 g H.sub.2O and 1043 g of KOH) using a controlled
double jet injection method with constant stirring. The slurry thus
formed was diluted to a volume of 8330 mL with deionized water, and
heated in a sealed stainless steel vessel, i.e., a hydrothermal
reactor, at 300.degree. C. for 6 hours with agitation. After the
slurry was discharged from the hydrothermal reactor, the slurry was
decanted several times before being subjected to cross-flow washing
until a conductivity of 0.075 mS was achieved. The slurry was then
subjected to a Dual-Frequency Reactor (Advanced Sonic Processing
Systems) for sonification at a flow rate of about 50 ml/minute. The
resultant final CeO.sub.2 particles exhibited a primary particle
size of about 17 nm and a secondary particle size of about 800 nm.
A slurry of 1 wt % CeO.sub.2 particles was prepared in water
adjusted to a pH of 4 with HNO.sub.3). This slurry was used for
copper CMP on a Strasbaugh 6EC polisher with 3/1 psi & 60/60
rpm and with a slurry flow rate of 170 ml/min. A Cu removal rate of
1004 .ANG./min was obtained. The particle distribution was (d10) 50
nm, (d50) 120 nm, and (d90) 400 nm, and the particles exhibited a
crystallite size of 17 nm.
EXAMPLE 2
[0037] In a 500 ml beaker, 85.16 g of cerium ammonium nitrate
Ce(NH.sub.4).sub.2(NO.sub.3).sub.6 was dissolved in 300 ml
deionized water, and 6.34 grams (0.0157 mol) of ferric nitrate
nonahydrate (Fe(NO.sub.3).sub.3.9H.sub.2O) was added with stirring.
The solution was diluted further by addition of 350 ml of deionized
water. A basic solution was formed by dissolving 48.72 grams of
potassium hydroxide (KOH) in 350 ml deionized water. The solutions
(1) containing cerium ammonium nitrate and ferric nitrate and (2)
the base were simultaneously introduced under stirring into a 1000
ml beaker via a controlled double jet injection method. After the
solutions were added together, the resulting solution was stirred
for 5 minutes and then ultrasonicated for 15 min. The solution was
transferred to a sealed 1000 ml stainless steel reaction cylinder,
and then placed in a preheated oven at 300.degree. C. for 4 hours.
The reaction cylinder was removed from the oven, cooled to room
temperature, and the contents were transferred to a 1000 mL plastic
container. The reaction product consisted of a dispersion of cerium
oxide-ferric oxide composite nanoparticles. The product slurry was
then washed to remove excess unreacted ionic salts. The dispersion
was ultrasonicated for 15 minutes and then filtered to afford a
final product with pH 4.+-.0.5 and conductivity less than 0.07 mS.
The final product was filtered through 12-micron filter to remove
possible external impurities. The Cu CMP slurry was made by
diluting the above particles to a 1 wt % dispersion using deionized
water adjusted to a pH of 4 using nitric acid (HNO.sub.3). The Cu
CMP operation of Example 1 was performed using the composite Ce--Fe
particles this formed. A Cu removal rate of 1762 .ANG./min was
obtained. This indicates that the Ce--Fe composite particle is
chemically more active than the pure CeO.sub.2 nanoparticles used
in the comparative example. The particle distribution is (d10) 88
nm, (d50) 143 nm, and (d90) 346 nm, and the particles exhibited a
crystallite size of 10 nm.
EXAMPLE 3
[0038] A dispersion of cerium oxide-copper oxide composite
nanoparticles was formed using the same materials and procedure set
forth in Example 1, except that 13.36 g of copper nitrate
hemipentahydrate (Cu(NO.sub.3).sub.2.2.5H.sub.2O) was used instead
of ferric nitrate nonahydrate. The Cu CMP was performed under the
same conditions as in Example 1. A Cu removal rate of 2021
.ANG./min was obtained, indicating that Ce--Cu composite
nanoparticles are chemically more active than pure CeO.sub.2
particles. The particle distribution is (d10) 158 nm, (d50) 316 nm,
and (d90) 747 nm, with a crystallite size of 7.4 nm.
EXAMPLE 4
[0039] A dispersion of cerium oxide-neodymium oxide composite
nanoparticle dispersion was formed using the same materials and
procedure set forth in Example 1, except that 11.85 grams of
neodymium (III) nitrate hexahydrate (Nd(NO.sub.3).sub.3.6H.sub.2O)
was used instead of ferric nitrate nonahydrate. The Cu CMP was
performed under the same conditions as in Example 1. A Cu removal
rate of 1980 .ANG./min was obtained, indicating that Ce--Nd
composite nanoparticles are chemically more active than pure CeO2
nanoparticles. The particle distribution is (d10) 89 nm, (d50) 157
nm, and (d90) 437 nm and the particles exhibited a crystallite size
of 6.3 nm.
EXAMPLE 5
[0040] Composite cerium oxide particles were made in the following
manner. Except for the identity and amount of guest reagent added,
the syntheses were substantially identical. In a 1000 ml beaker,
80.2 g (0.146 moles) of cerium ammonium nitrate
Ce(NH.sub.4).sub.2(NO.sub.3).sub.6 was dissolved in 200 ml
deionized water to form a well mixed aqueous solution of cerium
salt. To the solution 18.95 g (0.036 moles) of acetyl acetone
titanate was added. The salt solution was well mixed until it was
clear and homogeneous. A sufficient quantity of DI-water was then
added to reach a final volume of 300 ml. In another 1000 ml plastic
bottle, 48.7 g (0.338 moles) of potassium hydroxide (KOH) was added
to DI water and diluted to a final volume of 300 ml. Using a
controlled double jet injection the salt solution and the base
solution are mixed together with continuous agitation, and mixed an
additional 5 minutes. The slurry is then ultrasonicated for 15
minutes. The slurry is then transferred to a stainless steel
reaction vessel and placed in a preheated oven at 300.degree. C.
for 4 hours. The stainless steel reaction vessel is removed from
the furnace and allowed to cool to room temperature. The reaction
product (a dispersion of cerium oxide-titanium oxide particles) is
then transferred to a clean 1000 ml container. The dispersion was
washed with DI water several times to remove excess ions and to
achieve subsequent separation from supernatants by settling. This
was carried out several times until the ion concentration was very
low (conductivity of 0.07 mS). The final product was filtered
through a 12-micron filter to remove any possible external
impurities.
[0041] FIG. 1 is a Table showing the molar amounts of guest ion
reagents that were mixed with Ce(NH.sub.4).sub.2(NO.sub.3).sub.6 to
produce the composite particles in accordance with the invention.
Sample 1 is the particle made by the exemplary synthesis of Example
5. The table further displays several properties of the composite
particles. The secondary particle size distribution of the
composite abrasive particles was determined by a light scattering
technique as known in the art, using a Horiba LA-910 particle size
analyzer. The secondary particle size is defined as the size of
agglomerates of primary particles.
[0042] The slurry was adjusted to a pH of 4 and the solid content
adjusted to 1% before use in CMP. The particles have the polishing
rate in angstroms per minute as set forth in FIG. 1. Polishing
experiments were performed using Westech 372 polisher using
six-inch silicon oxide wafers. An IC-1000/Suba-IV polishing pad was
used for polishing. The downward pressure on the carrier was set at
3.5 psi. The back pressure on the wafer carrier was 0 psi. The
carrier was rotated at speed of 93 rpm while the pad was rotated at
87 rpm. The slurry feed rate to the wafer-pad area was 150 ml. The
slurries used for the study are maintained at room temperature
(25.degree. C.). The films studied were PECVD TEOS silicon dioxide
on 150 mm diameter silicon wafer. The film thickness, before and
after CMP, was measured optically using a Prometrics FT-750.
[0043] It is noted that sample 34 in Table 1 is a comparative
example, inasmuch as it is a pure cerium oxide particle. Lacking
guest metal ions, the cerium oxide particle of sample 34 exhibits a
polishing rate on a silicon dioxide substrate of 3.14
.ANG./min.
EXAMPLE 6
[0044] To study the STI polishing performance of abrasive particles
with different mole percentages of titanium ions in the crystal
structure, 11 samples of abrasive particles were synthesized using
the procedures and reagents described in Example 5 above to produce
particles having the mole percentages of ceria and/or titania shown
in Table 1 below:
1 TABLE 1 Sample Ce/Ti (mole %) Raw D.sub.50 Raw Dmean (nm) 6-1
100/0 78 426 6-2 90/10 473 504 6-3 80/20 249 247 6-4 70/30 561 677
6-5 60/40 714 719 6-6 50/50 918 918 6-7 40/60 799 803 6-8 30/70 852
854 6-9 20/80 67 79 6-10 10/90 67 70 6-11 0/100 69 71
[0045] The particles were dispersed in water at a weight percent
loading of 1%. HNO.sub.3 was added to adjust the pH of the slurries
to 4.0. No chemical oxidizers and/or surfactants were added to the
slurries, and the slurries were not sonicated or filtered after
formation.
[0046] Samples 6-1 through 6-11 were used separately to polish
6-inch blanket thermal oxide (TOX) and nitride (NIT) wafers using a
Westech 372 polisher, an IC-1000/Suba-IV pad, with a downward
pressure of 3.5 psi (no back pressure), a carrier/pad rotation
speed of 93/87 rpm, and a slurry feed rate of 150 ml/min. Polishing
was conducted using the slurries first on a dummy silicon wafer,
then on a used TOX wafer, then on a new TOX wafer and finally on a
new NIT wafer. Distilled water was used to clean the wafers, which
were air-dried. Polishing results are shown in Table 2 below, where
"WIWNU" means WIthin Wafer Non-Uniformity:
2 TABLE 2 Polish rate (nm/min) Polish rate (nm/min) Polish rate
(nm/min) Surface TOX/NIT Sample TOX Used WIWNU TOX2 New WIWNU Avg
TOX NIT WIWNU Rough (nm) Selectivity 6-1 4.1 35.53% -1.2 37.60%
1.45 0.5 47.59% 1-1.5 2.9 6-2 339.1 24.04% 261.9 26.48% 300.5 197.9
6.38% 1-1.2 1.518444 6-3 43.6 34.53% 36.3 36.04% 39.95 224.3 7.09%
1.1-1.5 0.17811 6-4 399.5 15.45% 232.5 15.80% 316 234.6 5.10%
0.9-1.5 1.346974 6-5 335.9 11.74% 352.5 9.72% 344.2 159.2 5.05%
1.7-1.9 2.16206 6-6 300.1 12.32% 260.4 13.50% 280.25 18.3 36.33%
0.8-2.0 15.31421 6-7 196.4 16.85% 168.3 16.74% 182.35 2.7 33.11%
2.1-3 67.53704 6-8 260.6 9.40% 251.9 11.98% 256.25 96.3 6.50%
1.1-1.4 2.660955 6-9 90.9 16.29% 110.8 17.83% 100.85 2.7 37.34%
1.4-1.9 37.35185 6-10 N/A N/A 4.6 29.61% 4.6 28.9 22.32% 1.2-1.5
0.15917 6-11 N/A N/A 19.7 29.09% 19.7 23.3 26.34% 1.1-1.2
0.845494
[0047] The results shown in Table 2 above show that pure ceria
particles (i.e., containing no titanium ions) did not polish TOX or
NIT wafers at a very high rate. The removal rate increased as
titanium ions were introduced into the ceria crystal structure, and
then decreased as the concentration of titanium ions reached about
70 mole percent. In the case of pure titania, both TOX and NIT
removal rates were very low due to the inherent properties of
titania particles.
[0048] The TOX wafer surface for the slurries containing between 50
mole % and 80 mole % titanium ions are very rough due to the large
secondary particle sizes and the presence of needle-like particles,
which lead to some scratches on the wafers. In the case of 70 mole
% titanium ions, a better result may be attributable to a
comparatively small after formulation secondary particle size
(Dmean=338 nm vs. 404-1188 nm). In the range of 10 mole % to 40
mole % titanium ions, the TOX polishing rate is high and the
nitride removal rate is ideally not very high. The results for
Sample 6-3 (i.e., the 20 mole % titanium ions sample) are
questionable and may not be reliable.
[0049] The primary particle size increased in relation to the
increases in titanium ions present, with the lattice constant
decreasing from 5.42 .ANG. for pure ceria to 3.81 .ANG. for pure
titania. The lattice constant remained similar to pure ceria until
the mole percentage of titanium ions reached about 50 mole %. After
that point, the crystal structure of the ceria-titania composite
abrasive particles became more similar titania, which means that
cerium ions were guest ions and titanium ions were the host ions in
the crystal structure, which was anatase. Particles of this type
were not as good for oxide polishing as particles that exhibited a
substantially cubic crystal structure.
EXAMPLE 7
[0050] Abrasive particles were formed in accordance with the
procedures and using the reagents and equipment as described in
Example 5, except that the mole percentage of titanium cations to
cerium cations was 5.95% (Ti) to 94.05% (Ce). The raw mean particle
size (D.sub.50) of the abrasive particles was 79 nm. The abrasive
particles were dispersed at different loadings in water to form
slurries. No chemical oxidizers or surfactants were added, and the
slurries were not sonicated or filtered. The pH of the slurries was
adjusted using HNO.sub.3 or KOH. Slurry 7-1 included 1.0% by weight
of the abrasive particles and had a pH of 4. Slurry 7-2 included
1.0% by weight of the abrasive particles and had a pH of 10. Slurry
7-3 included 0.5% by weight of the abrasive particles and had a pH
of 4. And, Slurry 7-4 included 1.5% by weight of the abrasive
particles and had a pH of 4.
[0051] The slurries were separately used to 6-inch blanket thermal
oxide (TOX) and nitride (NIT) wafers using the same equipment and
procedures used in Example 6. The polishing results are shown in
Table 3 below:
3 TABLE 3 Polish rate (nm/min) Polish rate (nm/min) Polish rate
(nm/min) Surface TOX/NIT Sample TOX Used WIWNU TOX2 New WIWNU Avg
TOX NIT WIWNU Rough (nm) Selectivity 7-1 15.9 28.18% 19.1 9.29%
17.5 148.45 1.73% 1.1-1.3 0.1178848 7-2 117.6 39.52% 92.6 11.78%
105.1 124.4 23.37% 1.3-1.4 0.8448553 7-3 179.6 11.95% 152.2 22.72%
165.9 114.6 20.37% 1.2-2.1 1.447644 7-4 37.7 22.79% 24.4 14.65%
31.05 197.75 34.92% 0.9-1.0 0.1570164
[0052] The basic pH value 1 0 may be a little closer to the IEP of
hydrothermally created ceria particles (IEP=.about.8.5), resulting
in a pronounced increase of secondary particle size after slurry
formulation (Dmean=416 nm at pH=10 vs. 149 nm at pH=4), and thus
higher oxide removal rate and rougher surface finish. It is
somewhat surprising that an increase in TOX polishing rate was
observed when the weight percent of abrasive particles at a pH of 4
was reduced from 1.0% (Slurry 7-1) to 0.5% (Slurry 7-3). It is
possible that the relatively large secondary particles from Slurry
7-2 may have contaminated and been retained as residue on the
polishing pad during the polishing with Slurry 7-3. It is also
possible that the more dilute slurry (Slurry 7-3) provides more
opportunities for the abrasive particles to contact the wafer and
pad and thus results in a higher removal rate.
[0053] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
illustrative examples shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *