WO2006119249A2 - Aerogels and methods of using the same for chemical mechanical planarization and for extracting metal ions - Google Patents

Abstract

Methods for extracting or removing metal ions from a solution or system of interest include employing aerogels comprising (i) silica, and (ii) a polymer comprising at least one functional group capable of coordinating or binding a metal ion. Methods for removing or extracting metal ions from a system include providing compositions providing such aerogels, adding such compositions to a system that includes a metal to be removed therefrom, allowing the aerogel to reside in the system for a period of time sufficient to coordinate or bind metal ions, and removing the aerogel from the system. Also disclosed are chemical mechanical planarization compositions comprising an oxidizing agent and an aerogel comprising silica and a polymer having at least one functional group capable of coordinating metal ions, and is a chemical mechanical planarization process employing such chemical mechanical planarization compositions.

Description

AEROGELS AND METHODS OF USING

THE SAME FOR CHEMICAL MECHANICAL PLANARIZATION

AND FOR EXTRACTING METAL IONS

[0001] This application claims priority to and the benefit of U.S. Provisional

Application Number 60/675,991 , filed April 29, 2005, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] The present disclosure relates, in , various embodiments thereof, to aerogels or aerogel compositions comprising silica and a polymer, wherein the polymer is capable of acting as a grinding agent and coordinating metal ions. Such aerogels are also referred to herein as polymer-silica aerogels. The disclosure further relates to methods of using such compositions to remove or extract metal ions from a system such as a solution or slurry. Such compositions find particular application in conjunction with a chemical mechanical planarization process, and various embodiments are described with particular reference thereto. However, it is to be appreciated that polymer-silica aerogels are also amenable to other applications wherein one or more metal ions are to be extracted or removed.

[0003] Aerogels comprise a special class of highly porous solids with high surface areas and low densities. Synthetically, aerogels often are derived from sol-gels. In that approach, a sol is prepared first and allowed to transform into a gel. If the solvent is extracted without collapsing the pores from the gel, as by supercritical fluid extraction, an aerogel can be formed. The aerogel has a higher porosity than a xerogel, along with a lower density.

[0004] Common precursors used in syntheses of silica-based aerogels include organosilicates. Both tetramethoxysilane (TMOS) and tetrathoxysilane (TEOS) can act as a precursor. The sol-gel synthetic pathway is based on a well known series of hydrolysis and condensation reactions between individual organosilicate molecules, creating network structures in the gel.

[0005] Polymeric chains can be incorporated in silica aerogels. Certain types of polymers can be dispersed uniformly in the silica matrix, and not form a completely separate phase from that of the silica particles. Such polymers have been shown to play a role in the gellation of the sol. [0006] In this regard, the bio-derived polymer chitosan has been of interest due to its functional amine groups as disclosed in U.S. Patent No. 6,303,046 and an article by Xipeng Liu, et al., Mat. Res. Symp. Proc. 740 (2003), each of which is fully incorporated herein by reference in its entirety. Chitosan-silica aerogel composites have been successfully synthesized and have the high surface area, porosity and low density associated with normal silica aerogels. However, the chitosan drastically influences the amount of time required for gellation. The gel time for a typical chitosan/TEOS system is 8-10 hours, while it takes the analogous TEOS system 70 hours to gel by itself. [0007] Further, as disclosed in an article by Xiangjun Hu et al. in Mat. Res. Symp.

Proc. 702 (2002) and U.S. Patent No. 6,303,046, both of which are fully incorporated herein by reference in their entirety, transition metal ions such as Ru(III), Rh(III), and Pd(II) have been incorporated into chitosan-silica aerogels via complexation with the amine group of chitosan. Typically, the metal ions were introduced into the synthesis during the wet-gel phase as an ethanolic or aqueous solution. U.S. Patent No. 6,303,046 discloses a printing medium comprising polymer-silica-metal aerogels. [0008] In some instances it may be necessary or desirable to remove or extract metal ions or metal ion complexes from a particular environment or system. Examples of such systems may include, but are not limited to, waste waters, systems associated with mining applications, and the like. Another example of a system that requires removal or extraction of metal ions is a process associated with forming integrated circuits.

[0009] An integrated circuit ("IC"), is an interconnected array of active and passive elements integrated with a single semiconductor substrate or deposited on the substrate by a continuous series of compatible processes, and capable of performing at least one complete electronic circuit function. Integrated circuits are typically formed from millions of active devices formed on a silicon substrate that are interconnected to form functional circuits and components. In back-end IC manufacturing, thin layers of metals (conductors) are layered with dielectric materials in order to form electrical interconnections between active components of the circuit.

[0010] Along this line, copper, because of its good electronic and thermal properties, is commonly used as a conductor in the production of semiconductor chips. Generally, electrical connections are made through metallized trenches or wells. For example, with reference to Figures 1A and 1B, a circuit 10 may be formed by depositing a dielectric film 14, such as a doped or undoped silicon dioxide (SiO₂) or a low-K dielectric on a substrate 12. Trenches or wells 18 are created in the dielectric film such as by etching. A thin barrier layer 16, is formed over the dielectric layer and into the trenches or wells. The barrier layer is typically formed from tantalum or tantalum nitride. The interconnections are made by depositing a metal film 20 over the barrier layer and into the trenches or wells. The metal film deposition continues until the trench or hole is filled with the metal layer. Examples of metals used for the metal layer include, but are not limited to, copper, aluminum, silver and tungsten.

[0011] The copper damascene process is an example of a typical integral circuit manufacturing process. The copper damascene process begins with the formation of a dielectric layer utilizing various optical lithography and etching techniques. A barrier layer of tantalum is deposited by sputtering. After the barrier layer is in place, copper is deposited by electrode deposition. The deposition process produces topographically uneven surfaces.

[00121 In order to create isolated metal lines, for example copper lines, the excess metal and barrier layers must be removed. Excess metal may be removed by chemical mechanical planarization or polishing (CMP). Chemical mechanical planarization is a process of smoothing and planing surfaces with a combination of chemical and mechanical forces. CMP is most widely used in back-end integrated circuit (IC) manufacturing and is also essential in the assembly of Electro-Mechanical Systems and the manufacture of sub-micron 1C. Because of the different chemical properties of copper and tantalum, the removal step is usually done by CMP in two separate steps: removal of the excess metal, e.g., copper, and then removal of the tantalum based barrier layer.

[0013] Figure 1 C represents a desired planarized surface obtained by CMP. That is, ideally, the upper surface 22 as formed from the copper lines and the barrier layer is generally substantially planar. Figure 1 D represents a more likely result after CMP. As shown in Figure 1 D, the upper surface of the barrier layer has been eroded. The upper surface of the copper or metal layer is recessed relative to the upper surface of the dielectric layer, which is referred to as "dishing" of the metal. Dishing is undesirable because it reduces the metal line's final thickness and the resulting non-planar surface presents problems if further functional layers are to be added to the circuit. [0014] In principle, CMP polishes the layers through a combination of mechanical and chemical forces. In theory, the polishing could be accomplished with mechanical grinding forces alone, but when this is attempted, the damage to the resulting layers can be high. Chemical etching cannot planarize the metal itself, but it can assist in the removal of unwanted metals without the damage caused by the mechanical forces. [0015] Figure 2 shows a schematic drawing of one current CMP technology system. A circuit chip 40 to be planarized is placed in direct contact with a polishing pad 34 attached to platen 32. The pad 34 and platen 32 are rotated, such as by motor 50, while the circuit wafer 40 is held in place by a wafer 42 and maintained against the pad 34 by downward pressure. Optionally, the wafer may also be rotated, which may be controlled by motor 52. The rotation speed and downward pressure may be selected and controlled by the user as desired for a particular purpose or intended use. An abrasive and chemically reactive solution, referred to as a CMP slurry, is applied to the pad during planarization. The slurry contains both mechanical and chemically etching components. Typically, it is a delicate balance of oxidizing agents, surfactants, complexing agents and abrasives in a pH controlled aqueous solution. Abrasives used in CMP compositions include metal oxide abrasives such as silicas, cerias, alumina, titania, ziconia, germania, tantalum oxide, and the like. On the microscopic scale, the abraslveness of the particles grinding away portions of the excess metal can supply the force necessary for planarization. Planarization can be accomplished by the rotational movement of the pad relative to the substrate as the slurry is provided to the wafer/pad interface.

[0016] The manufacture of integrated circuits requires the use of a variety of metals. Because of its electronic and thermal properties, copper is replacing aluminum as the conductive layer. Tantalum, or tantalum nitride, is used as a barrier layer between the copper and the dielectric layer (often SiO₂). The barrier layer plays a dual role. First, it promotes the adhesion of the copper to the dielectric layer. Second, it reduces the diffusion of copper onto the dielectric layer. For ultra large-scale integrated circuits, tungsten is used as a plug for multilevel interconnections. Chemically, CMP has three major steps: oxidation of the metal, coordination of the ions, and removal. All three steps can occur within the slurry phase plus additional rinsing. Oxidation is required to convert the metal in the metal or metal-containing layer to an ionic form. Once in ionic form, the complexing agent coordinates the metal ions, which are then removed by washing or rinsing.

[0017] Current advances in CMP technology are focused on the nature and composition of the slurry because the slurry affects both the removal rate and the efficiency of the process. However, several problems still exist with current CMP technology. First, because a complexing agent is used, there is a possibility that the slurry will leave this complexing agent and complexed metal-containing species on top. Another problem is inadequate selectivity between the removal rates for the conductor, barrier, and insulator layers. This causes over-polishing of some layers, resulting in degradation of the layer. Additionally, the tantalum or TaN in the barrier layers and the metal(s) in the metal layer generally have distinct chemical properties such that planarization of each layer may need to be carried out in a separate CMP process. [0018] Thus, there remains a need for compositions and methods for removal of metal ions from various systems such as, for example, waste water systems. Further, there is also a need for providing new CMP compositions for use in CMP processes.

BRIEF DESCRlPTiON

[0019] In one aspect, the present disclosure provides aerogel compositions and methods of using the same for extracting or removing metal ions from a solution or system of interest. The methods preferably employ an aerogel or an aerogel composition that includes silica and at least one polymer having a functional group capable of binding to, or coordinating with, a metal ion.

[0020] In yet another aspect, the present disclosure provides a chemical mechanical planarization composition comprising an oxidizing agent and an aerogel composition comprising silica and at least one polymer comprising at least one functional capable of binding a metal ion.

[0021] In yet another aspect, the present disclosure provides a CMP composition comprising an oxidizing agent and an aerogel composition comprising silica and immobilized metal-coordinating functional groups selected from amine, hydroxyl, thiol, carboxyl, cyclic amine, sulfonate, amide, secondary amine, oxo, sulfide, disulfide and phosphonate groups.

[0022] In another aspect, the present disclosure provides, in various embodiments thereof, a method for extracting a metal ion from a system of interest. The method comprises providing an aerogel or aerogel composition comprising (i) silica, and (ii) a polymer comprising at least one functional group capable of coordinating a metal ion to be removed from a system; adding the aerogel or aerogel composition to a system comprising a metal ion to be removed therefrom; allowing the aerogel or aerogel composition to reside in the system for a period of time sufficient to extract a selected concentration of the metal ion to be removed from the system; and removing the aerogel or aerogel composition from the system.

[0023] In still another embodiment, the present disclosure provides a chemical mechanical planarization process. The process comprises providing a workpiece comprising a dielectric layer, an optional barrier layer disposed over the dielectric layer, and a metal layer disposed over the barrier layer; providing a chemical mechanical planarization composition comprising (a) an oxidizing agent, and (b) an aerogel composition comprising (i) silica, and (ii) a polymer comprising at least one functional group capable of coordinating a metal ion; and planarizing at least one of the metal layer and the barrier layer by using the chemical mechanical planarization composition between a platen and the metal layer of the workpiece. Alternatively, the aerogel can be a silica based aerogel containing a functional group selected from amine, hydroxy!, thiol, carboxyl, cyclic amine, sulfonate, amide, secondary amine, oxo, sulfide, disulfide and phosphonate groups.

[0024] Further aspects of the present disclosure will be further understood with reference to the detailed description. It should, however, be understood that the detailed description, exemplary embodiments, and specific examples, while indicating various embodiments in accordance with the present disclosure, are given by way of illustration only and they are not intended to limit the scope of the claims. [0025] These and other non-limiting aspects and/or objects of the development are more particularly disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The following is a brief description of the drawings, which are presented for the purposes of illustrating the development disclosed herein and not for the purposes of limiting the same.

[0027] Figure 1 A represents a cross-sectional view of an integrated circuit;

[0028] Figure 1B represents a cross-sectional view of an integrated circuit comprising a metal layer;

[0029] Figure 1 C illustrates a cross-sectional view of a desired or ideal integrated circuit after undergoing a chemical mechanical planarization process;

[0030] Figure 1 D illustrates a cross-sectional view of an integrated circuit that exhibits dishing after undergoing a chemical planarization process; [0031] Figure 2 is a schematic representation of a chemical planarization system;

[0032] Figure 3 is a representation of an exemplary method for extracting metal ions from a source of interest utilizing a polymer-silica aerogel;

[0033] Figure 4 is a representation of an exemplary chemical mechanical planarization process employing a chemical mechanical planarization composition in accordance with the present disclosure;

[0034] Figure 5 illustrates synthetic pathways for forming a pectic acid-silica aerogel and a chitosan-silica aerogel;

[0035] Figure 6 represents UV- Vis spectra and standard line for trials examining removal of copper from a solution utilizing a polymer-silica aerogel;

[0036] Figure 7 represents UV- Vis spectra and standard line for trials examining removal of tungsten from a solution utilizing a polymer-silica aerogel;

[0037] Figure 8 represents UV-Vis spectra and standard line for trials examining removal of cerium from a solution utilizing a polymer-silica aerogel;

[0038] Figure 9 represents UV-Vis spectra and standard line for trials examining tantalum removal from a solution utilizing a polymer-silica aerogel;

[0039] Figure 10 represents UV-Vis spectra and standard line for dual metal tantalum absorption trials;

[0040] Figure 11 represents UV-Vis spectra and standard line for dual metal copper absorption trials;

[0041] Figure 12 illustrates FTIR spectra from stability trials of chitosan-silica aerogels and pectic acid-silica aerogels in the presence of sodium iodate; and

[0042] Figure 13 illustrates FTIR spectra of chitosan-silica aerogels and pectic acid-silica aerogels in the presence of hydrogen peroxide.

DETAILED DESCRIPTION

[0043] The present disclosure generally relates to a method or methods for removing metal ions from a system of interest utilizing an aerogel composition or aerogel comprising (i) silica, and (ii) a polymer having a functional group capable of coordinating a metal ion of interest.

[0044] The term "polymer" as used herein generally refers to a macromolecular substance composed _rof repeating atomic groups, i.e., monomers. The term encompasses all types of polymers such as, for example, homopolymers, copolymers, dimers, trimers, oligomers, and the like. [0045] The polymer incorporated into an aerogel may include any functional group or groups that is/are capable of binding metal ions. As used herein, the terms "binding," "complex," and "coordinate" and any derivatives thereof are used interchangeably. Suitable functional groups include, but are not limited to, amines, including primary amines, carboxyl groups, hydroxyl groups, sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, ketones, nitriles, sulfones, sulfonic acids, acylamine, cyclic amines, secondary amines sulfonates, oxos, phosphonates and the like. In one embodiment, a polymer incorporated into an aerogel comprises a single type of functional group. In another embodiment, a polymer incorporated into an aerogel comprise two or more different types of functional groups. Additionally, an aerogel may comprise a plurality of polymers wherein each polymer comprises functional groups that are capable of binding metal ions. In one embodiment where an aerogel comprises a plurality of polymers with such functional groups, at least two of the polymers have different functional groups.

[0046] Examples of suitable polymers include, but are not limited to, chitosan, pectic acid, alginic acid, carboxylate-modified poly(acryalmide), carboxylate modified chitosan, polyvinyl alcohol, carrageenans, polyamines, and the like. [0047] In one embodiment, the polymer is chitosan, which is the name given to materials derived from chitin by deacylation. These materials vary in degree of deacylation and molecular weight according to the source of the chitin and the deacylation process. Commercial chitosan typically is prepared from chitin from the skin or shell of anthropods and thus often is a recovered waste product of fishing industry. Chitosans in the range of 50 to 100 percent deacylated (replacement of 50 to 100 percent of acylamine groups by amine groups) and molecular weights in the 35,000 to 3,000,000 Dalton can be used. Suitable chitosans include, but are not limited to, those having weight average molecular weights in the range of about 150,000 to about 2,500,000 g/mol and degrees of deacylation from about 70 to about 100 percent. Particularly suitable chitosans include those with weight average molecular weights of about 300,000 to about 2,100,000 g/mol and degrees of deacylation from about 80 to about 100 percent.

[0048] Chitosan is a copolymer containing both beta-(1 -4)-2-acetamido-2-deoxy-

D-glucose and beta-1(1-4)-2-amino-2-deoxy-D-glucose units. The amine group of the deacylated units can form coordinate covalent bonds to metal ions by complexation. The extent to which the amine group, which coordinates to metal ions, is present relative to its protonated form depends on the pH of the system. A characteristic of chitosan that is unusual for compounds with primary amine groups is that a significant fraction of the groups are in the amine form at pH less than 7. Furthermore, this also means that chitosan can coordinate effectively at pH less than 7 rather than at the higher pH values at which the silica network is subject to base hydrolysis and instability. [0049] Another characteristic of chitosan is that it has OH groups. Without being limited to any particular theory, it is contemplated that the OH groups assist in the interaction of the polymer with the silica as it is present in the various stages of preparation and in the final form of aerogel material. This characteristic as well as the interactions of other groups of the chitosan copolymer with the silica, and of the OH groups with the metal ions and with other chitosan units may be the reason that the polymer is not extracted to a deleterious extent when the wet gel is exposed to aqueous metal ion containing solutions and alcohols.

[0050] In another embodiment, the polymer in the aerogel is pectic acid. Pectic acid comprises carboxyl functional groups that, similar to the amine groups such as in chitosan, can react with their surroundings and bind metal ions. [0051] The polymer, and/or the functional group, may be selected as desired for a particular purpose or intended use. For example, the polymer and/or functional group may be selected based on the type of metal ion to be removed from a solution, or from a process such as a chemical mechanical planarization process. The functional group can be incorporated in the aerogel by means other than in a functional polymer in the matrix for the CMP process. For example, silica aerogels are known that have amine, thiol or hydroxyl groups associated with the matrix by attachment directly or indirectly to the silicon atoms. The nature of the metal ion to be removed from a system may help determine the type of polymer or functional group to be employed to remove such metal ions. A polymer and/or functional group may be selected based on the known capability of the functional group or polymer to remove particular metals. For example, as previously described, it has been shown, such as in U.S. Patent No. 6,303,046, that amine functional groups, such as those on chitosan, can bind or complex transition metals such as Ru(III), Rh(III) and Pd(II). As described herein, amines and carboxyl groups are shown to effectively coordinate cobalt ions, including Co(Il), cerium ions, including Ce(IV), tungsten ions, including W(VI), and tantalum ions, including Ta(V). [0052] A functional group may also be selected based on the functional group's chemical nature. For example, functional groups having lone pairs of electrons, such as for example amines, may be suitable for binding or complexing metal ions. Additionally, a polymer or functional group may be selected based on whether the metal ion to be extracted is considered a hard or soft acid. Without being bound to any particular theory, hard acids typically complex with hard bases more efficiently than with soft bases, and similarly, soft acids typically complex with soft bases more efficiently than they would with hard bases. For example, Cu²⁺ is considered a soft ion and would be expected to complex to a soft base, such as an amine group. Thus, a polymer comprising amine functional groups may be particularly suitable to extract or coordinate copper (II) ions from a system. A person skilled in the art is capable of ascertaining or determining whether a metal ion is considered a hard or soft acid and whether a functional group is considered a hard a soft base. Therefore, a person skilled in the art is capable of selecting a polymer and/or functional group for removing a metal ion from a system of interest based on either (i) empirical data or (ii) general chemical knowledge as it relates to the chemical structure of the functional group, such as whether the functional group includes lone pairs of electrons, and/or the hardness or softness of the metal ion to be extracted and/or the hardness or softness of the polymer functional group. <

[0053] Aerogels comprising a polymer may be formed by mixing a polymer and a silica precursor, such as an organosilicate, together and forming a sol and/or a gel. Examples of suitable silica precursors include, but are not limited to, tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and the like. The gel is then formed into an alcogel. An aerogel is then formed by supercritically extracting the solvent from the alcogel using CO₂. Chitosan-silica aerogels and pectic acid-silica aerogels can be prepared as described in Shung Ji. Ph.D. Thesis- Brown University (2001), which is incorporated by reference in its entirety.

[0054] With reference to Figure 3, a method 60 for extracting a metal ion from a system of interest includes (a) providing a functionalized aerogel, as indicated in box 62 comprising (i) silica, and (ii) one or more functional groups capable of coordinating metal ions, the functional groups being directly or indirectly attached to a silicon of the aerogel or being provided as part of a polymer as previously described herein, (b) adding the aerogel to a system of interest, as indicated in box 64, in which the system comprises a metal ion to be removed from the system, and (c) removing the aerogel from the system, as indicated in box 68. The aerogel may be allowed to reside in the system, as indicated in 66, for any amount of time sufficient to remove a desired quantity or concentration of metal ions from the system. Additionally, as also indicated in box 66 in some systems, such as CMP process, the aerogel may be ground into a powder and also allowed to act as an abrasive for a period of time. [0055] Examples of metal ions that may be extracted from a solution include, but are not limited to, ions of Co, Cu, Fe, Cr, Ni, Mn, Rh, Ru₁ Ir, Pd, Pt, Yb, Er, Eu, Sm, and Dy.

[0056] In one embodiment, an aerogel comprising a polymer having functional groups capable of coordinating metal ions may be allowed to reside in a system of interest for a period of from about several seconds to several days. Of course shorter or longer periods of time may be selected as desired for a particular purpose or intended use.

[0057] In a method for extracting or removing metal ions from a system, an aerogel in accordance comprising silica and a polymer capable of coordinating a metal ion may be used alone or in a composition with other materials as may be needed or desired for the particular system.

[0058] The present disclosure also relates to chemical mechanical planarization compositions comprising (a) an oxidizing agent and (b) an aerogel that functions as both an abrasive and a complexing agent. As previously described herein, the aerogels are silica based, and silica is an abrasive material used in CMP pompositions. [0059] An aerogel for use in a CMP composition in accordance with the present disclosure comprises a functional group capable of complexing or coordinating metal ions, and in particular metal ions found in conjunction with CMP processes. [0060] In such aerogels, one or more functional groups are associated with aerogel matrix. As used herein, a functional group is associated with an aerogel matrix where the functional group is (i) attached either directly or indirectly to a silicon atom, or (ii) attached to another component or structure that is interspersed in the aerogel matrix. [0061] Suitable functional groups include, but are not limited to, primary amines, carboxyl groups, hydroxyl groups, sulfide, thiol, amide, pyridine and related cyclic amines, urethane, ether ketone, nitrile, sulfone, sulfonic acid, acrylamide, and the like. [0062] In one embodiment, a CMP composition comprise (a) an oxidizing and (b) an aerogel comprising functional groups capable of coordinating metal ions wherein the functional groups are directly or indirectly attached to a silicon atom of the aerogel matrix. [0063] In another embodiment, a CMP composition comprises (a) an oxidizing agent and (b) an aerogel comprising silica and a functionalized polymer capable of coordinating metal ions may be suitable for use in a chemical mechanical planarization composition and/or process.

[0064] A chemical mechanical planarization composition in accordance with the present disclosure comprises (a) an oxidizing agent and (b) an aerogel comprising silica and a polymer having functional groups capable of binding or coordinating metal ions. The polymer and/or functional group may be selected as desired to remove or extract any of one or more metal ions that require removal during a CMP process. In one embodiment, the silica based aerogel comprising polymer and/or functional group may be selected to both provide abrasivity and to remove ions of at least one of Cu₁ W, Ce, and/or Ta. In one embodiment the aerogel comprises chitosan. In another embodiment, the aerogel comprises pectic acid. In still another embodiment, the aerogel comprises chitosan and pectic acid.

[0065] The oxidizing agent may be selected from any material suitable as an oxidizing agent in a polishing composition. One of the steps in CMP is the oxidation of the metal layer to an ionic form. For copper, tantalum and tungsten this is an important step, as it allows forthe removal of the metal by taking it into a soluble form. By utilizing the oxidation chemistry of the metals, less mechanical work needs to be done, and this minimizes the damage caused by the mechanical grinding forces. As such, the oxidizing agent should be capable of oxidizing a metal, such as in the metal layer of an integrated circuit, to an ionic form. Examples of suitable oxidizing agents include, but are not limited to, hydrogen peroxide (H₂O₂), sodium iodate (NaIO₃), nitrates, ammonium persulfate, and the like.

[0066] In a CMP composition in accordance with the present disclosure, the aerogel must be stable in the presence of the oxidizing agent. Therefore the oxidizing agent may be selected on the desired aerogel to be employed in the composition, or the aerogel may be selected based on the oxidizing agent being used. [0067] Copper is a well studied metal. Its use in CMP comes from the fact that copper is second only to silver in its high thermal and electrical conductivities. [0068] Chemical mechanical planarization compositions in accordance with the disclosure may be suitable for use in a chemical mechanical planarization process. With reference to Figure 4, a chemical mechanical planarization process 70 comprises providing a workpiece, as indicated in box 72, such as, for example, a wafer or integrated circuit, providing a chemical mechanical planarization composition comprising an oxidizing agent and an aerogel comprising silica and one or more functional group capable of coordinating metal ions, as indicated in box 74, and planarizing at least one of a metal layer and/or a barrier layer on the workpiece, as indicated in box 76. In one embodiment, the chemical mechanical planarization process removes metal ions from the metal layer and allows for planarization of the metal layer. In another embodiment, the process removes metal ions from both the metal layer and barrier layer. The metal ions may be removed by any suitable method including, for example, rinsing, as indicated in box 78.

[0069] In still another embodiment, a chemical mechanical planarization composition in accordance with the present disclosure may be used in conjunction with other chemical mechanical planarization compositions. For example, in one embodiment a workpiece is subjected to a chemical mechanical planarization process by employing a first chemical mechanical planarization composition comprising an oxidizing agent, an abrasive that includes cerium or a cerium oxide, and a complexing agent. In this embodiment, the first chemical mechanical planarization composition does not include an aerogel. After the first planarization process, a second chemical mechanical planarization operation may be performed using a second chemical mechanical planarization composition comprising an oxidizing agent and an aerogel comprising silica and a polymer having functional groups that are capable of coordinating metal ions, in this case cerium ions, to remove cerium from the wafer or workpiece.

[0070] Methods and compositions in accordance with the present disclosure are further understood with respect to the following Examples. The Examples are for the purpose of illustrating various potential embodiments and not intended to limit the scope of the claims.

Examples

[0071] The ability of aerogels comprising silica and a polymer having functional groups suitable for coordinating metal ion were evaluated for their ability to extract metal ions from solution, because the ability of silica particles to function as abrasive is well known.

A. Aerogel Preparation [0072] Metal ion extraction was examined using chitosan-silica aerogels and pectic acid aerogels. The aerogels were prepared as described below. The synthetic pathway for preparing these aerogels is illustrated in Figure 6. [0073] The typical synthesis of chitosan-silica aerogels is as follows. Begin with

40 ml of 1 percent (w/w) aqueous chitosan solution. Add 12.5 ml of tetraethoxysilane (TEOS) and 0.9 ml glacial acetic acid. Stir vigorously for 8 hours, at which point the sol becomes clear. Transfer approximately 4 ml of sol into approximately 15-20 1.25 x 1.25 inch polystyrene boxes. Let the sol age overnight to form a clear, colorless gel. Divide a solution of 1.45 ml of ammonium hydroxide in ethanol evenly between all boxes, and let it stand for 24 hours. Replace the liquid on top of the gel with ethanol daily until ethanol is the primary solvent. Using high temperature arid pressure, supercritically extract the gels using carbon dioxide.

[0074] The typical preparation of pectic acid-silica aerogels begins with 40 ml of 1 percent (w/w) aqueous pectic acid solution titrated to pH = 4.0 with sodium hydroxide. Commercially available pectic acid was purchased from Aldrich Chemicals. Then, 7.6 ml tetramethoxysilane (TMOS) is added. Stir vigorously for 1 hour until the sol is clear. Transfer 4 ml aliquots of the sol into polystyrene boxes. The sol is aged overnight to form a clear, colorless gel. Add enough of a 2:1 (v/v) water/ethanol solution to completely cover the gel (approximately 3 ml). Replace the gel solvent daily, gradually increasing to 100 percent ethanol over a few days. Using high temperature and pressure, supercritically extract the gels using carbon dioxide. [0075] FTIR analysis was conducted using a Perkin Elmer 1600 FTIR with an N₂ purge to observe incorporation of the polymer into the aerogel. Aerogel pieces were selected to be quite clear and to be large enough to cover the infrared beam width when taped to the side of the sample holder. Also, the piece had to be thin enough in order for the beam to not be completely absorbed. Generally, pieces that were mostly transparent were used.

[0076] Single piece FTIR samples were run after synthesis of both the PA-SiO₂ and X-SiO₂ aerogels in order to observe the incorporation of the polymer inside the aerogel matrix. Since the aerogel trials were run using ground aerogel, no aerogel piece large enough existed for single piece FTlR analysis. In these cases, a sample was prepared using a KBr pellet. A small amount of ground aerogel was mixed with ground KBr. The mixture was then pressed into a mostly transparent pellet. The pellet was then placed in the sample holder of the FTIR. [0077] FTIR spectrum of a single piece of the PA-SiO₂ aerogel, indicated successful incorporation of the pectic acid into the aerogel. A shoulder at approximately 1700 cm^"1 was observed and is indicative of the carboxyl groups on the polymer. Since the silica has no carboxyl groups of its own, the signal must come from incorporation of the polymer. Also, the presence of the shoulder implies that the carboxyl groups are free and not bound to anything within the gel. Without being bound to any particular theory, this allows for coordination with the metal ions.

[0078] FIRR spectra also indicated successful incorporation of the chitosan polymer into an aerogel. In the case of chitosan, the amine groups are visible. Peaks at 1550 and 1595 cm^"1 were observed and respectively assigned to the free amine groups. Silica aerogels without chitosan do not have any absorbance in this range, so the peaks can be assigned to the amine groups on the chitosan. Again, their presence and location imply that the amine groups are free and available to complex with the metal ions.

B. Metal Ion Extraction Using Aerogels with Functionalized Polymers

[0079] The metals examined in this study are copper, tantalum, tungsten, and cerium. These metals were selected for their importance in the manufacture of integrated circuits of all types and to demonstrate the feasibility of employing aerogels comprising functionalized polymers in a CMP composition. Cerium was also of interest, because it is the other main abrasive (in place Of SiO₂) used in IC manufacturing. The trials were run in solution, beginning with the metal in the oxidized ion form. [0080] 1. Colorimetric Methods

Colorimetric Ultraviolet-Visible (UV-Vis) analysis was employed to determine how effective polymer-silica aerogels are in removing the selected ions from solution. For UV-Vis spectroscopy, the absorbance is directly proportional to the concentration of the solution. The Beer-Lambert law states:

A = log₁₀(l_Q/l) = εcb

where A is the absorbance of the light, I₀ is the initial intensity of the light, I is the intensity of the transmitted light, ε is the molar absorptivity, b is the length of the system (sample cell) and c is the concentration of the absorbing species. [0081] The molar absorptivity is a constant that is specific to each absorbing system and wavelength. As long as the composition of the system and the wavelength do not change, the molar absorptivity is constant. However, if the nature of the system changes with concentration (i.e. the equilibrium is shifted to a different species) then the Beer-Lambert law may not hold as ε is different for each species. [0082] The four metals under investigation have very different chemical properties, so a separate colorimetric method was required for each metal. All UV analysis was completed on a Perkin Elmer 3500. Scans were run from 200 to 800 nm using a quartz cell with a width of 1 mm.

[0083] The colorimetric analysis of copper is very well documented. One colorimetric method is based on the reaction of copper with ammonium hydroxide to form a blue color. To calibrate the method for this study, stock solutions of copper were made by dissolving copper (II) nitrate (Cu(NO₃)₂) in distilled water. An amount of ammonium hydroxide was added to slightly exceed four times the amount of [Cu(H₂O)₆J²⁺. Upon addition of the NH₄OH, a blue color developed due to the formation of a copper-amine complex. The UV absorbance was measured at 634 nm. A standard curve was constructed from a series of six known samples. [0084] Cerium has a very straight forward colorimetric analysis. When eerie ammonium nitrate is dissolved in water, the solution has a yellow color. The yellow is thought to be due to a cerium-ammonia complex. The UV absorbance was measured at 287 nm. Five stock solutions at varying concentrations were used to create a standard curve for cerium analysis.

[0085] The colorimetric determination of tungsten is well documented. Sodium tungstate was dissolved in distilled water for a stock solution. Three other solutions were required. First, 50.0 g of sodium thiocyanate was dissolved in 100 ml of distilled water. Second, 50.0 g of tartaric acid was dissolved in 100 ml of distilled water. And third, 70.0 g of stannous chloride (dihydrate) was added to 1 L of concentrated hydrochloric acid. After stirring for approximately 1 hour, the stannous chloride solution became clear.

[0086] The colorimetric method for W (Vl) is as follows. First, 10 ml of the tungsten solution is added to a 50 ml volumetric flask. Then, 2 ml of tartaric acid solution and 1.5 ml of the sodium thiocyanate solution is added. The solution is diluted to 50 ml by the stannous chloride solution. After sitting for 20 minutes, the UV absorption is measured at 400 nm. Five known concentration solutions were used to construct the standard curve. In this procedure, the time between mixing the components and the time of measurement is critical. Take the UV measurements at 20 minutes after mixing. The reaction proceeds with time, and the 20 minute time frame is an integral part of the method.

[0087] Relatively little has been published about aqueous tantalum chemistry, although it has important applications in the integrated circuit industry. Most of the colorimetric methods found in the literature are focused on issues involving the metallurgy of tantalum and its separation from other metals, particularly niobium. For this reason, a reliable colorimetric method of tantalum needed to be developed. [0088] While no fully satisfactory colorimetric method exists for tantalum, a literature review lead to a method involving pyrogallol by G. Chariot. Colorimetric Determination of Elements. Elsevier Publishing Company. Amsterdam: 1964. However, the determination was complicated, involved the use of strong acids (H₂SO₄) and a mostly aqueous system. A derivative of the pyrogallol determination was located. The approach is to react TaCI₅ with gallic acid in ethanol, a solvent in which TaCI₅ is stable.

[0089] The first colorimetric trials of tantalum began as close as possible to the published gallic acid determination (Kazunobu Kodama. Methods of Quantitative Inorganic Analysis, lnterscience Publishers. New York: 1963.) The published procedure assumed a starting material of impure tantalum oxide, and involved a fusion with potassium bisulfate step to produce a soluble species. In this work, TaCI₅ was purchased.

[0090] In the procedure, a saturated solution of ammonium oxalate was prepared by dissolving 2.52 g (NHJ₂C₂O₄ in distilled water. Then, 1 x 10^ g TaCI₅ and 5 mg K₂S₂O₇ were added to 40 ml of the ammonium oxalate solution. A gallic acid solution was made by adding 4.0 g gallic acid to 100 ml of a 1 :1 (v/v) EtOH:H₂O mixture. Then, 5.0 ml of the gallic acid solution was added to the ammonium oxalate/tantalum/potassium sulfate solution. Upon addition of the gallic acid solution, a yellow color formed. The yellow is due to a tantalum-gallate complex, the exact nature of which is unknown. Upon UV analysis, however, no identifiable peak was found. [0091] To determine the chemistry of the color formation the previously desired published procedure was broken down and the roles of various components were evaluated. First, the role of the sulfate was questioned. A new trial was run without the potassium sulfate. Thus, 22.5 ml of the saturated oxalate solution was combined with 2.5 ml of the gallic acid solution and 0.001 g OfTaCI₅. A yellow color still formed. After sitting for approximately 30 min, a precipitate appeared at the bottom of the flask. Without being bound to any particular theory, the precipitate was believed to be due to the reaction of the tantalum ions with the water to form the insoluble oxide. This later was shown to be incorrect. The precipitate formed was determined by FTlR analysis to be ammonium oxalate "crashing out" of solution. The same procedure was repeated using different amounts of tantalum. UV analyses were done on all samples. A peak was observed in the UV spectrum. Absorbance measurements were taken at 316 nm. A line correlating the tantalum concentration to absorbance was found, with a correlation coefficient of r = 0.99565 and standard deviation SD = 0.1123. [0092] Using this method, the first aerogel trials were conducted. A stock solution of 1 x 1 C⁴ M TaCI₅ was made. Half of the solution was a control, while the other half was the experimental solution. To the experimental solution, 0.14918 g of ground pectic acid-silica aerogel was added. This made the ratio of Ta ions to carboxyl groups approximately 1:10. After setting overnight, the solution was vacuum filtered to remove aerogel particles. Both the control solution and the filtered experimental solution underwent the following colorimetric analysis. First, 30 ml of the tantalum solution was added to 15 ml of fresh saturated oxalate solution. Then, 5 ml of the fresh gallic acid solution was added to each flask. Both the control and experimental solutions being clear. UV analysis was conducted.

[0093] Two changes in the tantalum determination procedure were made for subsequent experiments. First, the amount of oxalate used was reduced. Instead of a saturated ammonium oxalate solution, a small amount of ammonium oxalate was added to the gallic acid solution. Also, the water was eliminated from the gallic acid solution. The gallic acid and ammonium oxalate were combined in 100 percent ethanol to form a stock colorimetric reagent for tantalum. An important note: in UV trials involving tantalum, a gallic acid background was used. The gallic acid solution has a brown color, which has an absorbance in the UV. This peak disappears as the gallic acid is complexed with the tantalum ions.

[0094] 2. Aerogel Extraction Tests of Single Metal Ions

[0095] UV analysis was used to determine the efficiency of the aerogel material in picking up the metal ions from solution. The efficiency of the aerogel is defined as:

Eff = 100 - fConc. After exposure to aerogel) x 100 (Cone. Before exposure to aerogel) [0096] Aerogel trials to evaluate copper extraction were run with both pectic acid- silica and chitosan-silica aerogels. In each aerogel trial, 0.1 g of ground aerogel was added to 3 ml of a stock Cu (II) solution. Trials were run with the initial solutions having [Cu(H₂O)₆]²* concentrations of 0.01 M, 0.003 M and 0.001 M. After the aerogel and Cu (II) solutions equilibrated for one hour, the suspension was filtered to remove most of the aerogel powder. Then, the suspension was centrifuged to pull any remaining aerogel out of the supernatant. The supernatant was removed, ammonia was added, and the solution was subjected to UV analysis as described above. [0097] When the beginning concentration of Cu²⁺ ions was 0.001 M, the X-SiO₂ aerogel had a much higher efficiency than the PA-SiO₂ aerogel. The efficiency of the PA-SiO₂ aerogel was 60 percent while the efficiency of the X-SiO₂ aerogel was 100 percent. As the initial concentration of the copper solution increased, the difference between the efficiencies decreased. Results are presented in table 1 and in Figure 6.

Table 1. Efficiencies of Copper Aerogel Trials

[0100] Aerogel trials to evaluate tungsten extraction were conducted using both chitosan-silican and pectic acid-silica aerogels. Procedurally, 0.1 g of ground aerogel was added to 3 ml of a sodium tungstate solution of known concentration. The aerogel suspension was allowed to sit overnight. After separating the aerogel from the suspensions and by centrifuging the solutions, quantitative UV analysis for WO₄ ^2" was conducted on the supernatant.

[0101] The UV analysis of tungsten provided results similar to those seen in the copper trials. The spectra are presented in Figure 7. In the case of W, the PA-SiO₂ aerogel was more efficient than the X-SiO₂ aerogel. Starting with an initial concentration of 0.005 M, the efficiency of the PA-SiO₂ was 74.86 percent and the efficiency of the X-SiO₂ was 35.18 percent.

[0102] The efficiency with which aerogels removed Ce (IV) ions from such a solution was measured using pectic acid-silica aerogels. 0.1 g of ground pectic acid-silica aerogel was added to 3.0 ml of (NH₄)₂Ce(NO₃)₆ solution. The mixture was allowed to sit overnight. The solution was then centrifuged and the supernatant was used for UV analysis. [0103] The UV analysis showed an efficiency of 99 percent when the starting solution had a concentration of 0.1 M. When the initial concentration was lowered to 0.01 M, the efficiency dropped to 93 percent. The results are shown in Figure 8. [0104] UV trials of tantalum were run using both PA-SiO₂ and X-SiO₂ aerogels. The efficiency of the PA-SiO₂ aerogel was 98.4 percent and the efficiency of the X-SiO₂ aerogel was 93 percent, beginning with a 0.01 M tantalum chloride solution. Figure 11 shows both the UV spectra and the calculated standard curve. [0105] The foregoing tests demonstrate that polymer-silican aerogels are able to pull metal ions out of solution. The copper UV trials demonstrated that both X-SiO₂ and PA- SiO₂ aerogels have the ability to complex with the copper ions in solution, making them feasible materials for copper CMP. The results of the UV trials, however, had an unexpected component. Copper (II) is a soft acid and theoretically should complex better with a soft rather than hard base. At lowest concentration, this was observed. The X-SiO₂ aerogel, with the soft amine groups, had a higher efficiency than the PA- SiO₂ aerogel, which contains hard carboxyl groups. When the initial concentration is increased, the PA-SiO₂ aerogel had a higher efficiency than the X-SiO₂. At the highest concentration, both aerogels had similar efficiencies. Without being bound to any particular theory, this can be explained through saturation of the functional groups. Both chitosan and pectic acid have similar molecular weights, so to a close approximation, there are the same number of amine groups as there are carboxyl groups in the same weight of their respective aerogel when made at the same polymer content (approximately 10 percent X/PA). The low efficiencies at high metal ion concentration could be the result of all the available functional groups being occupied. Since there is the same number of functional groups in both trials (approximately 4:1 functional groupsxopper ions), the efficiency values should be close to the same, if saturation is the limiting factor.

[0106] The tantalum trials are consistent with the hard/soft theory of acids and bases. Since Ta⁵⁺ is a hard acid, it should complex more efficiently with the carboxyl groups of pectic acid. The efficiency of X-SiO₂ was 93 percent as compared to an efficiency of 98.4 percent for PA-SiO₂ than with the amine groups of X-SiO₂. The UV results also suggest that tantalum can be picked up relatively efficiently with X-SiO₂. The exact nature of tantalum in solution is unknown, and it is likely that the ions are present in mixed oxidation states. Ions in a lower oxidation state would be softer and could coordinate well with the amine groups of chitosan. The ability OfX-SiO₂ to pick up tantalum ions may be useful in designing a CMP system in which the tantalum barrier layer and the copper connect layer are polished in the same step, but the greater efficiency of PA-SiO₂ would suggest that a mixture of X-SiO₂ and PA-SiO₂ would be superior to either alone. [0107] 3. Dual Metal Trials

[0108] Tests were also performed to evaluate the ability of one or more aerogels to extract two or more metals from solution. The procedure for the dual metal trials was as follows. A 100 ml solution with a concentration of 0.0028 M Cu²⁺ and 0.0054 M Ta⁵⁺ was made. The solution was a yellow-green color. This solution was diluted twice: once by 1/2, then by half again (ending concentrations % of the original concentration). These dilutions were used to construct the standard curve for both copper and tantalum solutions. Then, 0.3 g Of X-SiO₂ aerogel was added to 6 ml of the most concentrated solution, and the same was repeated with PA-SiO₂. A third trial was run where 0.15 g of X-SiO₂ and 0.15 g of PA-SiO₂ were both added to the same 6 ml of concentrated solution. After sitting for 3 hours, the solutions were centrifuged and the supernatant was used for UV analysis.

[0109] The UV analysis of the dual metal trials changed slightly due to the nature of the solution. First, the copper concentration was measured. The yellow-green color is assigned to Cu²⁺ ions coordinating with the Cl^" ions originating from TaCI₅ to form CuCI₄ ^2". The copper concentration was determined by direct measure of the absorbance at 291 nm of the supernatant. Analysis of the tantalum ion concentration was then conducted (as described in the next section) by adding 2 ml of a gallic acid solution (0.02 g gallic acid in 500 ml EtOH) to 0.5 ml of the trial solution. The absorbance was then measured at 312 nm. This was close to the original tantalum absorbance measured at 316 nm for the single metal trials.

[0110] The dual metal trial results are summarized in Table 2. Samples A, B and C were used to construct the standard lines for the UV analysis. Both the standard line and spectra are presented in Figures 10 and 11. The shaded values were calculated from the standard curve. The numbers in parenthesis are the calculated efficiency values for each trial.

After PA-SiO₂ 0.00257 (8.2 0.00003 (99.5 1.018 0.005 was added percent) percent)

After X-SiO₂ 0.00187 (33.2 0.00009 (98.4 0.747 0.015 was added percent) percent)

After both 0.00239 (14.6 0.00003 (99.5 0.949 0.005 aerogels were percent) percent) added

C. Aerogel Stability

[0111] FTIR spectroscopy was used to investigate the stability of the aerogels in commonly used oxidizing agents. The CMP process requires an oxidizer be present in the slurry in order to oxidize the metals into ions to allow for coordination and subsequent removal. In order for the aerogels to be potential materials in CMP, no major decomposition can occur in the presence of oxidizing agents over a useful working period. Two different oxidizers, H₂O₂ and NaIO₃, were chosen based on a review of current literature. For example, H₂O₂ is a commonly used oxidizer in tantalum CMP. The stability of the aerogels in NaIO₃ also was investigated. The iodate ion is important oxidizing agent for copper and tungsten CMP.

[0112] First, both aerogels soaked in a 3 percent H₂O₂ solution. The aerogel was filtered out using vacuum filtration and pressed into a KBr pellet for FTIR analysis. Stability in NaIO₃ also was investigated. Pieces of both aerogels were soaked in a 0.1 M aqueous NaIO₃ solution overnight. The aerogels were vacuum filtered and allowed to dry. The particles were pressed into KBr pellets for FTIR analysis. All spectra were run on KBr pellets, as previously described with respect to FTIR analysis on the polymer- silica aerogels alone. Both the PA-SiO₂ and X-SiO₂ aerogels were stable in NaIO₃, as evidenced by the fact that there was no change between the before and after exposure spectra (Figure 12). Neither spectra showed degradation of either the polymer, or the silica matrix.

[0113] Similar results were found with respect to H₂O₂. After exposure to a solution of H₂O₂, no change in the FTIR spectra of either aerogel was found (Figure 13). Again, neither the polymer nor the silica matrix was altered significantly by the oxidizer. [0114] Since the IR spectra show no noticeable change in either the functionality or structure of aerogel, it can be concluded that the aerogel remains largely unaffected by the oxidizing agent under these limited conditions. Also, from the IR spectra, it can be seen that the functional groups remain intact. While this does not demonstrate directly that the polymers remain in their original polymeric form, it does show that the oxidizing agents have no effect on either the amine or carboxyl groups. Also the IR spectra show that the functional groups remain inside the aerogel and are free to participate in metal coordination. In summary, both the X-SiO₂ and PA-SiO₂ aerogels demonstrated stability when exposed to oxidizing agents under the experimental conditions. [0115] The foregoing demonstrates that polymer-silica aerogels are able to efficiently pick up metal ions from solution. Given the nature of these materials, such aerogels may be used in a CMP composition. Regarding their use in CMP applications, polymer- silica aerogels have several advantages over current slurries. The first lies in the fact that the polymer is held inside the silica particles. One potential problem with the current CMP technology is the possibility that a coordinated-metal layer may be present on top of the desired layer. In conventional CMP slurries, the coordinating agent is free within the slurry, and the only way to remove all of the coordinated complexes is through rinsing the slurry off. However, this still leaves the possibility of the coordinating agent remaining on the layer, if it is complexed with a metal atom. In polymer-silica aerogels, because the coordinating functional groups are attached to the polymer inside the silica particles. Therefore, in using polymer-silica aerogels in CMP slurries, potentially, all of the groups may be removed with the silica. This reduces and may even prevent any possibility that the functional groups will remain on top of the desired layer.

[0116] Another potential advantage that the polymer-silica aerogels have over current CMP technology is selectivity. As previously discussed, one problem associated with CMP is overpolishing and/or dishing. In the dual metal trials, the amount of copper picked up was proportional to the amount of X-SiO₂ aerogel added. By carefully controlling the amount of each aerogel present, the amount of metal that can be absorbed may potentially be controlled and minimize any overpolishing that may occur.

[0117] The synthesis of the polymer-silica aerogels is gentle enough to allow for incorporation of a wide variety of polymers. The choice of polymer is dependent on which functional groups are needed for the coordination of the metal ions. Chitosan and pectic acid have two of the most common functional groups that can complex metals. The amine groups on chitosan are able to handle the softer metal ions, while the carboxyl groups on pectic acid can coordinate the harder, lanthanide-type ions. Also, it is possible to adjust the amount of polymer added to the aerogel in order to increase the number of functional groups per gram of aerogel. This could reduce the amount of aerogel material required and increase the efficiency. Ultimately, the nature of the aerogel composites allows for many options in polymer selection and concentration.

[0118] A method for extracting metal ions from a system using a polymer-silica aerogel as well as CMP compositions and methods using such aerogels has been described with reference to various exemplary embodiments. Modifications and alterations may occurto others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1. A chemical mechanical planarization composition comprising: an oxiding agent; and an aerogel comprising (i) silica; and

(ii) at least one polymer comprising at least one functional group capable of binding a metal ion.

2. The chemical mechanical planarization composition according to claim 1 , wherein the at least one functional group is selected from an amine group, a carboxyl group, a hydroxy! group, sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, ketones, nitriles, sulfones, sulfonic acids, acylamine, cyclic amines, secondary amines sulfonates, oxos, phosphonates, or combinations thereof.

3. The chemical mechanical planarization composition according to claim 1 , wherein the polymer comprises an amine functional group.

4. The chemical mechanical planarization composition according to claim 1 , wherein the polymer comprises a carboxyl functional group.

5. The chemical mechanical planarization composition according to claim 1 , wherein the polymer is selected from chitosan, pectic acid, alginic acid, gelatin, carboxylate-modified poly(acrylamide), carboxylate modified chitosan, polyvinyl alcohol, amylopectin, polyamines, and combinations thereof.

6. The chemical mechanical planarization composition according to claim 1 , wherein the polymer is chitosan.

7. The chemical mechanical planarization composition according to claim 1 , wherein the polymer is pectic acid.

8. The chemical mechanical planarization composition according to claim 1 , wherein the composition further comprises a metal ion.

9. A chemical mechanical planarization composition comprising an oxidizing agent and an aerogel, wherein the aerogel comprises a silica and at least one functional group capable of binding a metal ion.

10. The chemical mechanical planarization composition according to claim 9, wherein the at least one functional group is selected from an amine group, a carboxyl group, a hydroxy! group, sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, tetones, nitriles, sulfones, sulfonic acids, acylamine, cyclic amines, secondary amines sulfonates, oxos, phosphonates, or combinations thereof.

11. A chemical mechanical planarization process comprising providing a workpiece comprising a dielectric layer defining one or more trenches, a barrier layer disposed over the dielectric layer, and a metal layer disposed over the barrier layer; providing a chemical mechanical planarization composition comprising (a) an oxidizing agent and (b) an aerogel comprising (i) silica, and (ii) a polymer comprising at least one functional group capable of coordinating a metal ion; and planarizing at least one of the metal layer and the barrier layer by depositing the chemical mechanical planarization composition between a platen and the metal layer of the workpiece and rotating at least one of the platen and the workpiece.

12. The process according to claim 11 , wherein the polymer comprises a functional group selected from an amine group, a carboxyl group, a hydroxyl group sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, ketones, nitriles, sulfones, sulfonic acids, acylamine, cyclic amines, secondary amines sulfonates, oxos, phosphonates, and combinations thereof.

13. The process according to claim 11 , wherein the polymer comprises an amine group.

14. The process according to claim 11 , wherein the polymer comprises a carboxyl group.

15. The process according to claim 11 , wherein the polymer is selected from chitosan, pectic acid, and combinations thereof.

16. The process according to claim 11 , wherein the metal layer comprises a metal selected from copper, tungsten, tantalum, cerium, and combinations thereof.

17. The process according to claim 11, wherein the metal layer comprises copper.

18. The process according to claim 11 , wherein the oxidizing agent is selected from at least one of hydrogen peroxide and sodium iodate.

19. A method for extracting metal ions from a system of interest comprising: providing an aerogel comprising (i) silica, and (ii) a polymer comprising at least one functional group capable of coordinating a metal ion to be removed from a system; adding the aerogel to a system comprising a metal ion to be removed therefrom; allowing the aerogel to reside in the system for a period of time sufficient to extract a selected concentration of the metal ion to be removed from the system; and removing the aerogel from the system.

20. The method according to claim 19, wherein the metal ion is selected from a copper ion, a tungsten ion, a cerium ion, a tantalum ion, and combinations thereof.

21. The method according to claim 20, wherein the aerogel comprises a polymer selected from chitosan, pectic acid, and combinations thereof.

22. The method according to claim 20, wherein the at least one functional group is selected from an amine group, a carboxyl group, a hydroxyl group, sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, ketones, nitriles, sulfones, sulfonic acids, acylanime, cyclic amines, secondary amines sulfonates, oxos, phosphonates, and combinations thereof.

23. The method according to claim 19, wherein the at least one functional group is selected from an amine group, a carboxyl group, a hydroxyl group, sulfides, thiols, amides, pyridines and related cyclic amines, urethanes, ethers, ketones, nitriles, sulfones, sulfonic acids, acyiamine, cyclic amines, secondary amines sulfonates, oxos, phosphonates, and combinations thereof.