Composition and method for planarizing surfaces

A composition and a method for planarizing or polishing a surface with the composition are provided. The composition comprises a liquid carrier, a chemical accelerator, and solids comprising about 5-90 wt. % of fumed metal oxide, and about 10-95 wt. % of abrasive particles, wherein about 90% or more of the abrasive particles (by number) have a particle size no greater than 100 nm. The composition of the present invention is useful in planarizing or polishing a surface with high polishing efficiency, uniformity, and removal rate, with minimal defectivity, such as field loss of underlying structures and topography.

TECHNICAL FIELD OF THE INVENTION
 The present invention relates to a composition and method for planarizing
 or polishing a surface, such as the surface of a semiconductor or metal
 layer of a memory or rigid disk.
 BACKGROUND OF THE INVENTION
 Compositions for planarizing or polishing the surface of a substrate are
 well known in the art. 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 slurry composition.
 Typical abrasive materials include silicon dioxide, cerium oxide, aluminum
 oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for
 example, describes a method for chemically-mechanically polishing a metal
 layer by contacting the surface with a polishing slurry comprising high
 purity fine metal oxide particles in an aqueous medium.
 Conventional polishing compositions typically are not entirely satisfactory
 at planarizing semiconductor wafers. In particular, polishing slurries can
 have less than desirable polishing rates, and their use in
 chemically-mechanically polishing semiconductor surfaces can result in
 poor surface quality. Because the performance of a semiconductor wafer is
 directly associated with the planarity of its surface, it is crucial to
 use a polishing composition that has a high polishing efficiency,
 uniformity, and removal rate and leaves a high quality polish with minimal
 surface defects.
 The difficulty in creating an effective polishing composition for
 semiconductor wafers stems from the complexity of the semiconductor wafer.
 Semiconductor wafers are typically composed of a substrate, on which a
 plurality of transistors has been formed. Integrated circuits are
 chemically and physically connected into a substrate by patterning regions
 in the substrate and layers on the substrate. To produce an operable
 semiconductor wafer and to maximize the yield, performance, and
 reliability of the wafer, it is desirable to polish select surfaces of the
 wafer without adversely affecting underlying structures or topography. In
 fact, various problems in semiconductor fabrication can occur if the
 process steps are not performed on wafer surfaces that are adequately
 planarized.
 There have been many attempts to improve the polishing efficiency and
 uniformity of conventional polishing agents, while minimizing defectivity
 of the polished surface and damage to underlying structures or topography.
 For example, U.S. Pat. No. 5,340,370 describes a polishing composition
 comprising an abrasive, an oxidizing agent, and water, which purportedly
 yields an improved removal rate and polishing efficiency. Similarly, U.S.
 Pat. No. 5,622,525 describes a polishing composition comprising colloidal
 silica having an average particle size of 20-50 nm, a chemical activator,
 and demineralized water.
 A need remains, however, for compositions and methods that will exhibit
 desirable planarization efficiency, uniformity, and removal rate during
 the polishing and planarization of substrates, while minimizing
 defectivity, such as surface imperfections and damage to underlying
 structures and topography during polishing and planarization. The present
 invention seeks to provide such a composition and method. These and other
 advantages of the present invention will be apparent from the description
 of the invention provided herein.
 BRIEF SUMMARY OF THE INVENTION
 The present invention is directed to a composition for planarizing or
 polishing a surface. The polishing composition of the present invention
 comprises (a) a liquid carrier, (b) a chemical accelerator, and (c) solids
 comprising about 5-90 wt. % of fumed metal oxide and about 10-95 wt. % of
 abrasive particles, wherein about 90% or more of the abrasive particles
 (i.e., by number) have a particle size no greater than 100 nm. The present
 invention also provides a method of planarizing or polishing a surface
 comprising contacting the surface with the composition of the present
 invention.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention provides a composition comprising (a) a liquid
 carrier, (b) a chemical accelerator, and (c) solids comprising about 5-90
 wt. % of fumed metal oxide and about 10-95 wt. % of abrasive particles,
 wherein about 90% or more of the abrasive particles (by number) have a
 particle size no greater than 100 nm. The composition is useful in
 planarizing or polishing a surface. The present invention allows for a
 high polishing efficiency, uniformity, and removal rate of a surface with
 minimal defectivity, such as field loss of underlying structures and
 topography.
 The total solids can be present in any suitable concentration in the
 composition of the present invention. The solids desirably are present in
 a concentration of about 0.1 wt. % or more (e.g., about 0.1-40 wt. %).
 Preferably, the total solids concentration is about 0.1-30 wt. % (e.g.,
 about 1-30 wt. %) of the composition.
 The solids of the composition of the present invention comprise about 5-90
 wt. % of fumed metal oxide and about 10-95 wt. % of abrasive particles
 (i.e., the abrasive particles are at least about 10 wt. % of the total
 solids). The solids of the composition desirably comprise about 10-85 wt.
 % (e.g., about 15-75 wt. %) of fumed metal oxide and about 15-90 wt. %
 (e.g., about 25-85 wt. %) of abrasive particles (i.e., the abrasive
 particles are at least about 15 wt. % (e.g., at least about 25 wt. %) of
 the total solids). Preferably, the solids comprise about 15-60 wt. %
 (e.g., about 20-50 wt. %) of fumed metal oxide and about 40-85 wt. %
 (e.g., about 50-80 wt. %) of abrasive particles (i.e., the abrasive
 particles are at least about 40 wt. % (e.g., at least about 50 wt. %) of
 the total solids).
 The fumed metal oxide of the composition of the present invention can be
 any suitable fumed (pyrogenic) metal oxide. Suitable fumed metal oxides
 include, for example, fumed alumina, fumed silica, fumed titania, fumed
 ceria, fumed zirconia, fumed germania, and fumed magnesia, coformed
 products thereof, cofumed products thereof, and mixtures thereof.
 Preferably, the fumed metal oxide of the composition of the present
 invention is fumed silica.
 Any suitable abrasive particles can be present in the composition of the
 present invention. Desirable abrasive particles are metal oxides. Suitable
 metal oxides include alumina, silica, titania, ceria, zirconia, and
 magnesia. Also suitable for use in the composition are abrasive particles
 prepared in accordance with U.S. Pat. No. 5,230,833 and various
 commercially available products, such as the Akzo-Nobel Bindzil 50/80
 product and the Nalco 1050, 2327, and 2329 products, as well as other
 similar products available from DuPont, Bayer, Applied Research, Nissan
 Chemical, and Clariant. Preferably, the abrasive particles of the
 composition of the present invention are a condensation-polymerized metal
 oxide, e.g., condensation-polymerized silica. Condensation-polymerized
 silica typically is prepared by condensing Si(OH).sub.4 to form colloidal
 particles.
 The abrasive particles of the composition of the present invention are such
 that about 90% or more of the abrasive particles (by number) have a
 particle size no greater than 100 nm. Preferably, the abrasive particles
 are such that at least about 95%, 98%, or even substantially all (or
 actually all) of the abrasive particles (by number) have a particle size
 no greater than 100 nm. These particle size preferences for the abrasive
 particles (i.e., whereby at least about 90%, 95%, 98%, substantially all,
 and all of the abrasive particles (by number) are no greater than a
 specific size of abrasive particle) also can pertain to other particle
 sizes, such as 95 nm, 90 nm, 85 nm, 80 nm, 75 nm, 70 nm, and 65 nm.
 Similarly, the abrasive particles of the composition of the present
 invention can be such that at least about 90%, 95%, 98%, or even
 substantially all (or actually all) of the abrasive particles (by number)
 have a particle size no less than 5 nm. These particle size preferences
 for the abrasive particles (i.e., whereby at least about 90%, 95%, 98%,
 substantially all, and all of the abrasive particles (by number) are no
 less than a specific size of abrasive particle) also can pertain to other
 particle sizes, such as 7 nm, 10 nm, 15 nm, 25 nm, and 30 nm.
 The abrasive particles of the composition of the present invention can be
 essentially bimodal in distribution in terms of particle diameter, with
 about 30-70% (e.g., about 50%) of abrasive particles (by number) ranging
 in size from about 30-50 nm and about 30-70% (e.g., about 50%) of abrasive
 particles (by number) ranging in size from about 70-90 nm. Preferably, the
 abrasive particles are essentially bimodal in distribution in terms of
 particle diameter, with about 30-70% (e.g., about 50%) of abrasive
 particles (by number) ranging in size from about 35-45 nm and about 30-70%
 (e.g., about 50%) of abrasive particles (by number) ranging in size from
 about 75-85 nm.
 The percentage values used herein to describe the nature of the abrasive
 particles in terms of particle size are percentages "by number," rather
 than being weight percentages, unless otherwise noted. The particle size
 of the abrasive particles refers to the particle diameter. The particle
 size can be measured by any suitable technique. The particle size values
 set forth herein are based on a visual inspection, specifically by way of
 transmission electron micrography (TEM), of a statistically significant
 sample of the abrasive particles, preferably at least 200 particles.
 The particle size distribution of abrasive particles can be characterized
 by geometric standard deviation by number, referred to as sigma-g
 (.sigma..sub.g). The .sigma..sub.g values can be obtained by dividing (a)
 the diameter at which 84% of the abrasive particles (by number) are less
 than by (b) the diameter at which 16% of the abrasive particles (by
 number) are less than (i.e., .sigma..sub.g =d.sub.84 /d.sub.16).
 Monodispersed abrasive particles have a .sigma..sub.g value of about 1. As
 the abrasive particles become polydispersed (i.e., include particles of
 increasingly different size), the .sigma..sub.g value of the abrasives
 particles increases above 1. The abrasive particles typically have a
 .sigma..sub.g value of about 2.5 or less (e.g., about 2.3 or less). The
 abrasive particles desirably have a .sigma..sub.g value of at least about
 1.1 (e.g., about 1.1-2.3 (e.g., 1.1-1.3), preferably a .sigma..sub.g value
 of at least about 1.3 (e.g., about 1.5-2.3 or even about 1.8-2.3).
 The composition of the present invention also can be characterized by
 packing density. The packing density is one minus the sedimentation volume
 of all of the composition components mixed together divided by the
 addition of the separate sedimentation volumes of the individual
 composition components. Thus, the packing density (PD) is 1-(V.sub.total
 /(V.sub.fmo +V.sub.ap)), wherein V.sub.fmo is the volume of the fumed
 metal oxide (in the absence of the abrasive particles), V.sub.ap is the
 volume of the abrasive particles (in the absence of the fumed metal
 oxide), and V.sub.total is the volume of the fumed metal oxide and
 abrasive particles mixed together. These volumes of the fumed metal oxide
 alone, abrasive particles alone, and the combination of the two in a mixed
 condition are determined by centrifuging the samples at any suitable
 G-force for a duration equal to 1.2.times.Stokes settling time of the
 smallest particle in the material for which the volume is being
 determined.
 The composition desirably has a packing density value of at least about
 0.1, preferably a packing density value of at least about 0.15. More
 preferably, the composition has a packing density value of at least about
 0.2. Most preferably, the composition of the present invention has a
 packing density value of at least about 0.3 (e.g., about 0.3-0.6) or even
 at least about 0.4 (e.g., about 0.4-0.6 or about 0.5-0.6). The composition
 of the present invention typically has a packing density value of about
 0.7 or less (e.g., about 0.65 or less or even about 0.6 or less).
 Any suitable chemical accelerator can be present in the composition of the
 present invention. The chemical accelerator acts to improve the
 planarization or polishing of a substrate, for example, as evidenced by an
 increased rate of substrate removal.
 Suitable polishing accelerators can include, for example, oxidizers,
 chelating or complexing agents, catalysts, and the like. Suitable
 oxidizers can include, for example, oxidized halides (e.g., chlorates,
 bromates, iodates, perchlorates, perbromates, periodates, mixtures
 thereof, and the like). Suitable oxidizers also can include, for example,
 perboric acid, perborates, percarbonates, nitrates, persulfates,
 peroxides, peroxyacids (e.g., peracetic acid, perbenzoic acid,
 m-chloroperbenzoic acid, salts thereof, mixtures thereof, and the like),
 permanganates, chromates, cerium compounds, ferricyanides (e.g., potassium
 ferricyanide), mixtures thereof, and the like. Suitable chelating or
 complexing agents can include, for example, carbonyl compounds (e.g.,
 acetylacetonates, and the like), simple carboxylates (e.g., acetates, aryl
 carboxylates, and the like), carboxylates containing one or more hydroxyl
 groups (e.g., glycolates, lactates, gluconates, gallic acid and salts
 thereof, and the like), di-, tri-, and poly-carboxylates (e.g., oxalates,
 phthalates, citrates, succinates, tartrates, malates, edetates (e.g.,
 disodium EDTA), mixtures thereof, and the like), carboxylates containing
 one or more sulfonic and/or phosphonic groups, and the like. Suitable
 chelating or complexing agents also can include, for example, di-, tri-,
 or poly-alcohols (e.g., ethylene glycol, pyrocatechol, pyrogallol, tannic
 acid, and the like) and amine-containing compounds (e.g., amino acids,
 amino alcohols, di-, tri-, and poly-amines, and the like). Suitable
 polishing accelerators also can include, for example, sulfates, halides
 (i.e., fluorides, chlorides, bromides, and iodides), and the like.
 It will be appreciated that many of the aforementioned compounds can exist
 in the form of a salt (e.g., a metal salt, an ammonium salt, or the like),
 an acid, or as a partial salt. For example, citrates include citric acid,
 as well as mono-, di-, and tri-salts thereof; phthalates include phthalic
 acid, as well as mono-salts (e.g., potassium hydrogen phthalate) and
 di-salts thereof; perchlorates include the corresponding acid (i.e.,
 perchloric acid), as well as salts thereof. Furthermore, certain compounds
 may perform more than one function. For example, some compounds can
 function both as a chelating and an oxidizing agent (e.g., certain ferric
 nitrates and the like).
 Preferably, the chemical accelerator of the present invention is ammonium
 persulfate, hydroxylamine nitrate, or iron (III) nitrate.
 Any suitable amount of chemical accelerator can be present in the
 composition of the present invention. The chemical accelerator desirably
 is present in the polishing composition in an amount of about 0.01-20 wt.
 % (i.e., about 0.01-15 wt. %). Preferably, the chemical accelerator is
 present in the composition of the present invention in an amount of about
 0.1-10 wt. %. More preferably, the chemical accelerator is present in the
 composition of the present invention in an amount of about 0.1-5 wt. %
 (i.e., about 0.1-2 wt. %).
 The composition of the present invention can further comprise one or more
 other components, such as surfactants, polymeric stabilizers or other
 surface active dispersing agents, pH adjusters, regulators, or buffers,
 and the like. Suitable surfactants can include, for example, cationic
 surfactants, anionic surfactants, nonionic surfactants, amphoteric
 surfactants, fluorinated surfactants, mixtures thereof, and the like.
 Suitable polymeric stabilizers or other surface active dispersing agents
 can include, for example, phosphoric acid, organic acids, tin oxides,
 organic phosphonates, mixtures thereof, and the like. Suitable pH
 adjusters, regulators, or buffers can include, for example, sodium
 hydroxide, sodium carbonate, sulfuric acid, hydrochloric acid, nitric
 acid, phosphoric acid, citric acid, potassium phosphate, mixtures thereof,
 and the like.
 Any suitable carrier (e.g., solvent) can be used in the composition of the
 present invention. A carrier is used to facilitate the application of the
 fumed metal oxide and abrasive particles onto the surface of a suitable
 substrate. A preferred carrier is water.
 The pH of the composition of the present invention is maintained in a range
 suitable for its intended end-use. The composition desirably has a pH of
 about 2-12. The preferred pH will depend on the particular chemical
 accelerator. For example, when the chemical accelerator is ammonium
 persulfate and NH.sub.3, then the pH preferably is about 9-11. When the
 chemical accelerator is iron (III) nitrate, then the pH preferably is
 about 2.5 or less, more preferably about 2. When the chemical accelerator
 is hydroxylamine nitrate, then the pH preferably is about 2-5.
 The present invention also provides a method of planarizing or polishing a
 surface. This method comprises contacting a surface with a composition as
 described herein. A surface can be treated with the composition by any
 suitable technique. For example, the composition can be applied to the
 surface through use of a polishing pad.
 The composition of the present invention is capable of planarizing or
 polishing a substrate at a relatively high rate, e.g., removing the
 silicon dioxide layer from a layered substrate at a relatively high rate.
 Furthermore, the composition of the present invention is well-suited for
 the planarizing or polishing of many hardened workpieces, such as memory
 or rigid disks, metals (e.g., noble metals), ILD layers, semiconductors,
 micro-electro-mechanical systems, ferroelectrics, magnetic heads,
 polymeric films, and low and high dielectric constant films. The
 composition also can be used in the manufacture of integrated circuits and
 semiconductors. The composition of the present invention exhibits
 desirable planarization efficiency, uniformity, removal rate, and low
 defectivity during the polishing and planarization of substrates.

EXAMPLES
 The following examples further illustrate the present invention but, of
 course, should not be construed as in any way limiting its scope.
 The memory or rigid disks, referenced in all but one of the following
 examples (i.e., Example 5), were commercially available memory or rigid
 disks obtained from Seagate Technology. The memory or rigid disks were
 nickel-phosphor coated (plated) disks with aluminum substrates. The memory
 or rigid disks had undergone a pre-polishing process prior to being used
 in the following examples, and each memory or rigid disk had a surface
 roughness of 30-50 .ANG..
 The memory or rigid disks were polished using a table top polishing machine
 manufactured by Streuers (West Lake, Ohio). The table top polishing
 machine employed a Rotopol 31 base and Rotoforce 3 downforce unit. The
 polishing pads used in each of the following examples were 30.48 cm (12
 inch) diameter Polytex Hi pads manufactured by Rodel. The memory or rigid
 disks were polished for 10 minutes per side using a platen speed of 150
 rpm, a polishing carrier speed of 150 rpm, and a slurry flow rate of 100
 ml/min. The polishing force used was 50 N.
 Nickel-phosphor removal rates in each of the following examples were
 calculated by weighing the clean, dry memory or rigid disk prior to
 polishing and following polishing. The weight loss was converted to a
 memory or rigid disk thickness loss using a nickel-phosphor density of
 8.05 g/cm.sup.3.
 Example 1
 This example illustrates the significance of the combination and ratio of
 fumed metal oxide to abrasive particles in the composition of the present
 invention, as well as the presence of a chemical accelerator, in
 maximizing the removal rate of a surface during planarization or polishing
 of that surface.
 Nickel-phosphor plated memory or rigid disks were polished separately with
 ten different compositions with total solids concentrations comprising
 varying relative concentrations of fumed silica (i.e., 0 wt. %, 25 wt. %,
 50 wt. %, 75 wt. %, and 100 wt. %), condensation-polymerized silica (i.e.,
 100 wt. %, 75 wt. %, 50 wt. %, 25 wt. %, and 0 wt. %) (measured median
 particle size of about 20 nm, .sigma..sub.g =2.26), and hydroxyamine
 nitrate (HAN) (i.e., either 0 wt. % HAN or 0.25 wt. % HAN). All of the
 compositions had a pH of about 3.5. The fumed silica was added to the
 compositions in the form of Cab-O-Sperse.RTM. SC-E fumed silica aqueous
 dispersion (Cabot Corporation). The condensation-polymerized silica was
 Bindzil.RTM. 50/80 (Akzo-Nobel), wherein about 90% or more of the
 particles thereof (by number) have a particle size no greater than 100 nm
 and about 90% or more of the particles thereof (by number) have a particle
 size no less than 5 nm. Following use of the polishing compositions, the
 removal rate of each composition was determined, with the resulting data
 set forth in Table 1.
 TABLE 1
 Relative Relative Wt. %
 Wt. % Condensation- Removal Rate (micro inch
 Fumed polymerized per minute) [.ANG./min]
 Composition Silica Silica No HAN 0.25 Wt. % HAN
 A 0 100 2.10 2.70
 [534] [686]
 B 25 75 2.28 3.40
 [579] [864]
 C 50 50 2.28 3.89
 [579] [988]
 D 75 25 2.10 5.70
 [534] [1448]
 E 100 0 1.41 1.70
 [358] [216]
 As is apparent from the data set forth in Table 1, the removal rates
 exhibited by the compositions with HAN were significantly greater than the
 removal rates of compositions without HAN. Moreover, the removal rates for
 compositions with HAN and solids consisting of about 25-75 wt. % fumed
 silica and 25-75 wt. % condensation-polymerized silica (Compositions B, C,
 and D) were greater than the removal rates for compositions with HAN and
 solids consisting of 100 wt. % fumed silica or 100 wt. %
 condensation-polymerized silica (Compositions A and E). These results
 demonstrate the significance of a combination of a chemical accelerator
 and a mixture of fumed metal oxide and abrasive particles possessing the
 particle size characteristics described herein, as well as the ratio of
 fumed metal oxide to abrasive particles, on the removal rate achievable by
 the composition of the present invention.
 Example 2
 This example illustrates the significance of the combination and ratio of
 fumed metal oxide to abrasive particles in the composition of the present
 invention, as well as the presence of a chemical accelerator, in
 maximizing the removal rate of a surface during planarization or polishing
 of that surface.
 Nickel-phosphor plated memory or rigid disks were polished separately with
 ten different compositions with total solids concentrations comprising
 varying relative concentrations of fumed silica (i.e., 0 wt. %, 25 wt. %,
 50 wt. %, 75 wt. %, and 100 wt. %), condensation-polymerized silica (i.e.,
 100 wt. %, 75 wt. %, 50 wt. %, 25 wt. %, and 0 wt. %) (measured median
 particle size of about 20 nm, .sigma..sub.g =2.26), ammonium persulfate
 (APS) and NH.sub.3 (i.e., either 0.25 wt. % APS and 0.25 wt. % NH.sub.3 or
 0 wt. % APS and 0 wt. % NH.sub.3). All of the compositions had a pH of
 about 10. The fumed silica was added to the compositions in the form of
 Cab-O-Sperse.RTM. SC-E fumed silica aqueous dispersion (Cabot
 Corporation). The condensation-polymerized silica was Bindzil.RTM. 50/80
 (Akzo-Nobel), wherein about 90% or more of the particles thereof (by
 number) have a particle size no greater than 100 nm and about 90% or more
 of the particles thereof (by number) have a particle size no less than 5
 nm. Following use of the polishing compositions, the removal rate of each
 composition was determined, with the resulting data set forth in Table 2.
 TABLE 2
 Relative Relative Wt. % Removal Rate (micro inch
 Wt. % Condensation- per minute) [.ANG./min]
 Fumed polymerized No APS 0.25 Wt. % APS
 Composition Silica Silica No NH.sub.3 0.25 Wt. % NH.sub.3
 A 0 100 2.10 2.80
 [534] [711]
 B 25 75 2.28 6.40
 [579] [1626]
 C 50 50 2.28 4.60
 [579] [1169]
 D 75 25 2.10 3.20
 [534] [813]
 E 100 0 1.41 0.85
 [358] [216]
 As is apparent from the data set forth in Table 2, the removal rates
 exhibited by the compositions with APS and NH.sub.3 were significantly
 greater than the removal rates of compositions without APS and NH.sub.3,
 except for the composition consisting of 100 wt. fumed silica. In
 particular, the removal rates for compositions with APS and NH.sub.3 and
 solids consisting of about 25-75 wt. % fumed silica and 25-75 wt. %
 condensation-polymerized silica (Compositions B, C, and D) were greater
 than the removal rates for compositions with APS and NH.sub.3 and solids
 consisting of 100 wt. % fumed silica or 100 wt. % condensation-polymerized
 silica (Compositions A and E). These results demonstrate the significance
 of a combination of a chemical accelerator and a mixture of fumed metal
 oxide and abrasive particles possessing the particle size characteristics
 described herein, as well as the ratio of fumed metal oxide to abrasive
 particles, on the removal rate achievable by the composition of the
 present invention.
 Example 3
 This example illustrates the significance of the combination and ratio of
 fumed metal oxide to abrasive particles in the composition of the present
 invention, as well as the presence of a chemical accelerator, in
 maximizing the removal rate of a surface during planarization or polishing
 of that surface.
 Nickel-phosphor plated memory or rigid disks were polished separately with
 ten different compositions with total solids concentrations comprising
 varying relative concentrations of fumed silica (i.e., 0 wt. %, 25 wt. %,
 50 wt. %, 75 wt. %, and 100 wt. %), condensation-polymerized silica (i.e.,
 100 wt. %, 75 wt. %, 50 wt. %, 25 wt. %, and 0 wt. %) (measured median
 particle size of about 20 nm, .sigma..sub.g =2.26), and Fe(NO.sub.3).sub.3
 (i.e., either 0 wt. % Fe(NO.sub.3).sub.3 or 0.25 wt. %
 Fe(NO.sub.3).sub.3). All of the compositions had a pH of about 2. The
 fumed silica was added to the compositions in the form of
 Cab-O-Sperse.RTM. SC-E fumed silica aqueous dispersion (Cabot
 Corporation). The condensation-polymerized silica was Bindzil.RTM. 50/80
 (Akzo-Nobel), wherein about 90% or more of the particles thereof (by
 number) have a particle size no greater than 100 nm and about 90% or more
 of the particles thereof (by number) have a particle size no less than 5
 nm. Following use of the polishing compositions, the removal rate of each
 composition was determined, with the resulting data set forth in Table 3.
 TABLE 3
 Relative Wt. %
 Relative Condensation- Removal Rate [.ANG./min]
 Wt. % Fumed polymerized No 0.25 Wt. %
 Composition Silica Silica Fe(NO.sub.3).sub.3
 Fe(NO.sub.3).sub.3
 A 0 100 534 1653
 B 25 75 534 1907
 C 50 50 579 2161
 D 75 25 579 2314
 E 100 0 358 1424
 As is apparent from the data set forth in Table 3, the removal rates
 exhibited by the compositions with Fe(NO.sub.3).sub.3 were significantly
 greater than the removal rates of compositions without Fe(NO.sub.3).sub.3.
 In particular, the removal rates for compositions with Fe(NO.sub.3).sub.3
 and solids consisting of about 25-75 wt. % fumed silica and 25-75 wt. %
 condensation-polymerized silica (Compositions B, C, and D) were greater
 than the removal rates for compositions with Fe(NO.sub.3).sub.3 and solids
 consisting of 100 wt. % fumed silica or 100 wt. % condensation-polymerized
 silica (Compositions A and E). These results demonstrate the significance
 of a combination of a chemical accelerator and a mixture of fumed metal
 oxide and abrasive particles possessing the particle size characteristics
 described herein, as well as the ratio of fumed metal oxide to abrasive
 particles, on the removal rate achievable by the composition of the
 present invention.
 Example 4
 This example illustrates the significance of the distribution of abrasive
 particle sizes in the composition of the present invention in maximizing
 the removal rate of a surface during polishing or planarization of that
 surface.
 Nickel-phosphor wafers were polished separately with nineteen different
 compositions, all having 0.25 wt. % hydroxylamine nitrate (HAN) and a
 total solids concentration of 4 wt. %, wherein the solids consisted of a
 varying concentration of fumed silica (1.6 wt. %, 2.4 wt. %, and 3.2 wt. %
 of the composition, or 40 wt. %, 60 wt. %, and 80 wt. % of the total
 solids, respectively) and a varying concentration of
 condensation-polymerized silica (2.4 wt. %, 1.6 wt. %, and 0.8 wt. % of
 the composition, or 60 wt. %, 40 wt. %, and 20 wt. % of the total solids,
 respectively), with the condensation-polymerized silica having varying
 relative concentrations of nominal 20 nm, 40 nm, and 80 nm
 condensation-polymerized silica particles (i.e., 0 wt. %, 0.4 wt. %, 0.8
 wt. %, 1.2 wt. %, 1.6 wt. %, and 2.4 wt. % of the composition). All of the
 compositions had a pH of about 3.5. The fumed silica was added to the
 compositions in the form of Cab-O-Sperse.RTM. SC-E fumed silica aqueous
 dispersion (Cabot Corporation). The 20 nm, 40 nm, and 80 nm
 condensation-polymerized silicas were 1050, PR-4291, and 2329 products
 (Nalco), respectively. The nominal 20 nm condensation-polymerized silica
 particles had a median particle size of about 25 nm and a .sigma..sub.g
 value of 1.20. The nominal 40 nm condensation-polymerized silica particles
 had a median particle size of about 46 nm and a .sigma..sub.g value of
 1.22. The nominal 80 nm condensation-polymerized silica particles had a
 median particle size of about 78 nm and a .sigma..sub.g value of 1.16. The
 condensation-polymerized silicas are commercially available materials
 wherein about 90% or more of the particles thereof (by number) has a
 particle size no greater than 100 nm and about 90% or more of the
 particles thereof (by number) have a particle size no less than 5 nm.
 Following use of the polishing compositions, the removal rate of each
 composition was determined, with the resulting data set forth in Table 4.
 TABLE 4
 Wt. % Wt. % Wt. % Wt. % Removal
 Compo- Fumed Nominal 20 Nominal 40 Nominal 80 Rate
 sition Silica nm Silica nm Silica nm Silica [.ANG./min]
 A1 3.2 0.8 0 0 1471
 A2 3.2 0 0.8 0 1326
 A3 3.2 0 0 0.8 1634
 B1 2.4 1.6 0 0 1021
 B2 2.4 0 1.6 0 1474
 B3 2.4 0 0 1.6 1639
 C1 1.6 2.4 0 0 826
 C2 1.6 0 2.4 0 788
 C3 1.6 0 0 2.4 1123
 D1 3.2 0.4 0.4 0 1748
 D2 3.2 0.4 0 0.4 1855
 D3 3.2 0 0.4 0.4 1685
 E1 2.4 0.8 0.8 0 1324
 E2 2.4 0.8 0 0.8 1283
 E3 2.4 0 0.8 0.8 1484
 F1 1.6 1.2 1.2 0 1207
 F2 1.6 1.2 0 1.2 1242
 F3 1.6 0 1.2 1.2 1143
 G1 3.2 0.267 0.267 0.267 2002
 As is apparent from the data set forth in Table 4, the removal rates
 exhibited by the compositions comprising hydroxylamine nitrate and solids
 consisting of a mixture of fumed silica and condensation-polymerized
 silica varied significantly with the particle sizes of the
 condensation-polymerized silica. These results demonstrate that the
 distribution of abrasive particle sizes in the composition of the present
 invention affects the removal rate achievable by the composition.
 Example 5
 This example illustrates the significance of the combination and ratio of
 fumed metal oxide to abrasive particles in the composition of the present
 invention, as well as the presence of a chemical accelerator, in
 maximizing the removal rate of a metal surface during planarization or
 polishing of that surface.
 Tungsten layers were polished separately with five different compositions,
 all having 4 wt. % hydrogen peroxide, 0.005 wt. % Fe (from ferric
 nitrate), 0.05 wt. % glycine, 0.03 wt. % malonic acid, and a total solids
 concentration of 2 wt. %, wherein the solids consisted of a varying
 concentration of fumed silica (i.e., 0 wt. %, 60 wt. %, 75 wt. %, 90 wt.
 %, and 100 wt. %), and a varying relative concentration of
 condensation-polymerized silica (i.e., 100 wt. %, 40 wt. %, 25 wt. %, 10
 wt. %, and 0 wt. %) (measured median particle size of about 40 nm,
 .sigma..sub.g =1.22). All of the compositions had a pH of about 2.3. The
 fumed silica was added to the compositions in the form of an aqueous
 dispersion of Cab-O-Sil.RTM. LM-150 fumed silica (Cabot Corporation). The
 condensation-polymerized silica was PR-4291 (Nalco), wherein the nominal
 40 nm condensation-polymerized silica particles had a median particle size
 of about 46 nm and a .sigma..sub.g value of 1.22. Following use of the
 polishing compositions, the removal rate of each composition was
 determined, with the resulting data set forth in Table 5.
 TABLE 5
 Relative Wt. %
 Condensation-
 Relative Wt. % polymerized Removal Rate
 Composition Fumed Silica Silica [.ANG./min]
 A 0 100 2062
 B 60 40 2001
 C 75 25 2046
 D 90 10 2715
 E 100 0 2234
 As is apparent from the data set forth in Table 5, the removal rate
 exhibited by the compositions with solids consisting of about 90 wt. %
 fumed silica and 10 wt. % condensation-polymerized silica (Composition D)
 was greater than the removal rates for compositions with solids consisting
 of 100 wt. % fumed silica or 100 wt. % condensation-polymerized silica
 (Compositions A and E). These results demonstrate the significance of a
 combination of fumed metal oxide and abrasive particles possessing the
 particle size characteristics described herein, as well as the ratio of
 fumed metal oxide to abrasive particles, on the removal rate achievable by
 the composition of the present invention.
 All of the references cited herein, including patents, patent applications,
 and publications, are hereby incorporated in their entireties by
 reference.
 While this invention has been described with an emphasis upon preferred
 embodiments, it will be obvious to those of ordinary skill in the art that
 variations of the preferred embodiments may be used and that it is
 intended that the invention may be practiced otherwise than as
 specifically described herein. Accordingly, this invention includes all
 modifications encompassed within the spirit and scope of the invention as
 defined by the following claims.